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0704.0501

Boris Dubrovin

B.Dubrovin, T.Grava, C.Klein

On universality of critical behaviour in the focusing nonlinear Schr\"odinger equation, elliptic umbilic catastrophe and the {\it tritronqu\'ee} solution to the Painlev\'e-I equation

32 pages, 10 figures

math.AP math-ph math.MP

We argue that the critical behaviour near the point of ``gradient catastrophe" of the solution to the Cauchy problem for the focusing nonlinear Schr\"odinger equation $ i\epsilon \psi_t +\frac{\epsilon^2}2\psi_{xx}+ |\psi|^2 \psi =0$ with analytic initial data of the form $\psi(x,0;\epsilon) =A(x) e^{\frac{i}{\epsilon} S(x)}$ is approximately described by a particular solution to the Painlev\'e-I equation.

0704.0502

Christine Vespa

Christine Vespa

Generic representations of orthogonal groups: projective functors in the category Fquad

32 pages

math.AT math.CT

In this paper, we continue the study of the category of functors Fquad, associated to F_2-vector spaces equipped with a nondegenerate quadratic form, initiated in two previous papers of the author. We define a filtration of the standard projective objects in Fquad; this refines to give a decomposition into indecomposable factors of the two first standard projective objects in Fquad. As an application of these two decompositions, we give a complete description of the polynomial functors of the category Fquad.

0704.0503

HongVan Le

Hong-Van Le

Manifolds admitting a $\tilde G_2$-structure

4 pages, a new shorter exposition is given. the result has been included as Appendix in arXiv:1912.03338

math.AT math.DG

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

We find a necessary and sufficient condition for a compact 7-manifold to admit a $\tilde G_2$-structure. As a result we find a sufficient condition for an open 7-manifold to admit a closed 3-form of $\tilde G_2$-type.

0704.0504

Chang Ho Hyun

Chang Ho Hyun

Compatibility of Exotic States with Neutron Star Observation

4 pages, 1 figure. A contribution to Yukawa International Seminar (YKIS) 2006, "New Frontiers in QCD", Kyoto, Japan, Nov. 20 - Dec. 8, 2006

Prog.Theor.Phys.Suppl.168:627-630,2007

10.1143/PTPS.168.627

nucl-th

We consider the effect of hard core repulsion in the baryon-baryon interaction at short distance to the properties of a neutron star. We obtain that, even with hyperons in the interior of a neutron star, the neutron star mass can be as large as $\sim 2 M_\odot$.

0704.0505

Hironobu Kihara

Hironobu Kihara, Muneto Nitta

Exact Solutions of Einstein-Yang-Mills Theory with Higher-Derivative Coupling

9 pages, more comments included

Phys.Rev.D76:085001,2007

10.1103/PhysRevD.76.085001

OCU-PHYS 263

hep-th gr-qc

We construct a classical solution of an Einstein-Yang-Mills system with a fourth order term with respect to the field strength of the Yang-Mills field. The solution provides a spontaneous compactification proposed by Cremmer and Scherk; ten-dimensional space-time with a cosmological constant is compactified to the four-dimensional Minkowski space with a six-dimensional sphere S^6 on which an instanton solution exists. The radius of the sphere is not a modulus but is determined by the gauge coupling and the four-derivative coupling constants and the Newton's constant. We also construct a solution of ten-dimensional theory without a cosmological constant compactified to AdS_4 x S^6.

0704.0506

Philipp Gegenwart

J.G. Donath, P. Gegenwart, F. Steglich, E.D. Bauer, J.L. Sarrao

Dimensional crossover of quantum critical behavior in CeCoIn$_5$

4 pages, 5 figures

Phys. Rev. Lett. 100, 136401 (2008)

10.1103/PhysRevLett.100.136401

cond-mat.str-el

The nature of quantum criticality in CeCoIn$_5$ is studied by low-temperature thermal expansion $\alpha(T)$. At the field-induced quantum critical point at H=5 T a crossover scale $T^\star\approx 0.3$ K is observed, separating $\alpha(T)/T\propto T^{-1}$ from a weaker $T^{-1/2}$ divergence. We ascribe this change to a crossover in the dimensionality of the critical fluctuations which may be coupled to a change from unconventional to conventional quantum criticality. Disorder, whose effect on quantum criticality is studied in CeCoIn$_{5-x}$Sn$_x$ ($0\leq x\leq 0.18$), shifts $T^\star$ towards higher temperatures.

0704.0507

Michael Duff

M. J. Duff and S. Ferrara

E_6 and the bipartite entanglement of three qutrits

15 pages latex, 3 figures, minor corrections

Phys.Rev.D76:124023,2007

10.1103/PhysRevD.76.124023

Imperial/TP/2007/mjd/1

hep-th quant-ph

Recent investigations have established an analogy between the entropy of four-dimensional supersymmetric black holes in string theory and entanglement in quantum information theory. Examples include: (1) N=2 STU black holes and the tripartite entanglement of three qubits (2-state systems), where the common symmetry is [SL(2)]^3 and (2) N=8 black holes and the tripartite entanglement of seven qubits where the common symmetry is E_7 which contains [SL(2)]^7. Here we present another example: N=8 black holes (or black strings) in five dimensions and the bipartite entanglement of three qutrits (3-state systems), where the common symmetry is E_6 which contains [SL(3)]^3. Both the black hole (or black string) entropy and the entanglement measure are provided by the Cartan cubic E_6 invariant. Similar analogies exist for ``magic'' N=2 supergravity black holes in both four and five dimensions.

0704.0508

Alexey Kulik

Yuri N.Kartashov, Alexey M.Kulik

Invariance principle for additive functionals of Markov chains

18 pages

math.PR

We consider a sequence of additive functionals {\phi_n}, set on a sequence of Markov chains {X_n} that weakly converges to a Markov process X. We give sufficient condition for such a sequence to converge in distribution, formulated in terms of the characteristics of the additive functionals, and related to the Dynkin's theorem on the convergence of W-functionals. As an application of the main theorem, the general sufficient condition for convergence of additive functionals in terms of transition probabilities of the chains X_n is proved.

0704.0509

Fulvia Confortola

Fulvia Confortola

Dissipative backward stochastic differential equations with locally Lipschitz nonlinearity

22 pages

Stochastic Processes and their Applications 117 (2007) 613-628

10.1016/j.spa.2006.09.008

math.PR

In this paper we study a class of backward stochastic differential equations (BSDEs) of the form dY(t)= -AY(t)dt -f_0(t,Y(t))dt -f_1(t,Y(t),Z(t))dt + Z(t)dW(t) on the interval [0,T], with given final condition at time T, in an infinite dimensional Hilbert space H. The unbounded operator A is sectorial and dissipative and the nonlinearity f_0(t,y) is dissipative and defined for y only taking values in a subspace of H. A typical example is provided by the so-called polynomial nonlinearities. Applications are given to stochastic partial differential equations and spin systems.

0704.0510

Osamu Seto

Osamu Seto and Masahide Yamaguchi

Axino warm dark matter and $\Omega_b - \Omega_{DM}$ coincidence

11 pages, no figure, typos corrected, references added, final version

Phys.Rev.D75:123506,2007

10.1103/PhysRevD.75.123506

IFT-UAM/CSIC-07-15

hep-ph astro-ph

We show that axinos, which are dominantly generated by the decay of the next-to-lightest supersymmetric particles produced from the leptonic $Q$-ball ($L$-ball), become warm dark matter suitable for the solution of the missing satellite problem and the cusp problem. In addition, $\Omega_b - \Omega_{DM}$ coincidence is naturally explained in this scenario.

0704.0511

Maurice Kibler

O. Albouy (IPNL), M. R. Kibler (IPNL)

A unified approach to SIC-POVMs and MUBs

15 pages

Journal of Russian Laser Research 28 (2007) 429-438

10.1007/s10946-007-0032-5

quant-ph math-ph math.MP

A unified approach to (symmetric informationally complete) positive operator valued measures and mutually unbiased bases is developed in this article. The approach is based on the use of operator equivalents expanded in the enveloping algebra of SU(2). Emphasis is put on similarities and differences between SIC-POVMs and MUBs.

0704.0512

Everaldo Arashiro

T\^ania Tom\'e and Kelly C de Carvalho

Stable oscillations of a predator-prey probabilistic cellular automaton: a mean-field approach

10 figures

10.1088/1751-8113/40/43/005

cond-mat.stat-mech

We analyze a probabilistic cellular automaton describing the dynamics of coexistence of a predator-prey system. The individuals of each species are localized over the sites of a lattice and the local stochastic updating rules are inspired on the processes of the Lotka-Volterra model. Two levels of mean-field approximations are set up. The simple approximation is equivalent to an extended patch model, a simple metapopulation model with patches colonized by prey, patches colonized by predators and empty patches. This approximation is capable of describing the limited available space for species occupancy. The pair approximation is moreover able to describe two types of coexistence of prey and predators: one where population densities are constant in time and another displaying self-sustained time-oscillations of the population densities. The oscillations are associated with limit cycles and arise through a Hopf bifurcation. They are stable against changes in the initial conditions and, in this sense, they differ from the Lotka-Volterra cycles which depend on initial conditions. In this respect, the present model is biologically more realistic than the Lotka-Volterra model.

0704.0513

John Southworth

John Southworth (1), B. T. Gaensicke (1), T. R. Marsh (1), D. de Martino (2), A. Aungwerojwit (1 and 3) ((1) University of Warwick, UK, (2) INAF - Osservatorio di Capodimonte, Italy, (3) Naresuan University, Thailand)

SDSS J233325.92+152222.1 and the evolution of intermediate polars

6 pages with 5 figures, accepted for publication in MNRAS

Mon.Not.Roy.Astron.Soc.378:635-640,2007

10.1111/j.1365-2966.2007.11796.x

astro-ph

Intermediate polars (IPs) are cataclysmic variables which contain magnetic white dwarfs with a rotational period shorter than the binary orbital period. Evolutionary theory predicts that IPs with long orbital periods evolve through the 2-3 hour period gap, but it is very uncertain what the properties of the resulting objects are. Whilst a relatively large number of long-period IPs are known, very few of these have short orbital periods. We present phase-resolved spectroscopy and photometry of SDSS J233325.92+152222.1 and classify it as the IP with the shortest known orbital period (83.12 +/- 0.09 min), which contains a white dwarf with a relatively long spin period (41.66 +/- 0.13 min). We estimate the white dwarf's magnetic moment to be mu(WD) \approx 2 x 10^33 G cm^3, which is not only similar to three of the other four confirmed short-period IPs but also to those of many of the long-period IPs. We suggest that long-period IPs conserve their magnetic moment as they evolve towards shorter orbital periods. Therefore the dominant population of long-period IPs, which have white dwarf spin periods roughly ten times shorter than their orbital periods, will likely end up as short-period IPs like SDSS J2333, with spin periods a large fraction of their orbital periods.

0704.0514

Radoslaw Hofman

Radoslaw Hofman

Complexity Considerations, cSAT Lower Bound

Presented at IMECS2007, presentation is avaliable here: http://www.teycom.pl/docs/ICCS_160_prez.pdf Awarded with Certificate of Merit for International Conference on Computer Science 2007 (ICCS2007)

IMECS2007 Conference Proceedings published by IAENG (ISBN: 978-988-98671-4-0)

math.LO math.CO

This article discusses completeness of Boolean Algebra as First Order Theory in Goedel's meaning. If Theory is complete then any possible transformation is equivalent to some transformation using axioms, predicates etc. defined for this theory. If formula is to be proved (or disproved) then it has to be reduced to axioms. If every transformation is deducible then also optimal transformation is deducible. If every transformation is exponential then optimal one is too, what allows to define lower bound for discussed problem to be exponential (outside P). Then we show algorithm for NDTM solving the same problem in O(n^c) (so problem is in NP), what proves that P \neq NP. Article proves also that result of relativisation of P=NP question and oracle shown by Baker-Gill-Solovay distinguish between deterministic and non-deterministic calculation models. If there exists oracle A for which P^A=NP^A then A consists of infinite number of algorithms, DTMs, axioms and predicates, or like NDTM infinite number of simultaneous states.

0704.0515

J. Peguiron

J. Peguiron, C. Bruder, B. Trauzettel

Temperature dependence of Coulomb drag between finite-length quantum wires

5 pages, 5 figures; v2: accepted version at PRL

Phys. Rev. Lett. 99, 086404 (2007)

10.1103/PhysRevLett.99.086404

cond-mat.mes-hall

We evaluate the Coulomb drag current in two finite-length Tomonaga-Luttinger-liquid wires coupled by an electrostatic backscattering interaction. The drag current in one wire shows oscillations as a function of the bias voltage applied to the other wire, reflecting interferences of the plasmon standing waves in the interacting wires. In agreement with this picture, the amplitude of the current oscillations is reduced with increasing temperature. This is a clear signature of non-Fermi-liquid physics because for coupled Fermi liquids the drag resistance is always expected to increase as the temperature is raised.

0704.0516

Gui Lu Long

Hao Guo, Gui Lu Long and Yang Sun

Effects of Imperfect Gate Operations in Shor's Prime Factorization Algorithm

8 pages 4 figures

Journal of the Chinese Chemical Society, 2001, 48: 449-454

quant-ph

The effects of imperfect gate operations in implementation of Shor's prime factorization algorithm are investigated. The gate imperfections may be classified into three categories: the systematic error, the random error, and the one with combined errors. It is found that Shor's algorithm is robust against the systematic errors but is vulnerable to the random errors. Error threshold is given to the algorithm for a given number $N$ to be factorized.

0704.0517

Jessica Tressou

Olivier Allais (CORELA), Jessica Tressou (METARISK, Hkust-Ismt)

Using decomposed household food acquisitions as inputs of a Kinetic Dietary Exposure Model

math.ST stat.TH

Foods naturally contain a number of contaminants that may have different and long term toxic effects. This paper introduces a novel approach for the assessment of such chronic food risk that integrates the pharmacokinetic properties of a given contaminant. The estimation of such a Kinetic Dietary Exposure Model (KDEM) should be based on long term consumption data which, for the moment, can only be provided by Household Budget Surveys such as the SECODIP panel in France. A semi parametric model is proposed to decompose a series of household quantities into individual quantities which are then used as inputs of the KDEM. As an illustration, the risk assessment related to the presence of methyl mercury in seafood is revisited using this novel approach.

0704.0518

Henrik Beuther

H. Beuther, Q. Zhang, E.A. Bergin, T.K. Sridharan, T.R. Hunter, S. Leurini

Dust and gas emission in the prototypical hot core G29.96-0.02 at sub-arcsecond resolution

Accepted for Astronomy and Astrophysics, 14 pages, 8 figures, 6 tables, high-resolution version of the paper available at http://www.mpia.de/homes/beuther/papers.html

10.1051/0004-6361:20066954

astro-ph

Aiming at a better understand of the physical and chemical processes in the hot molecular core stage of high-mass star formation, we observed the prototypical hot core G29.96-0.02 in the 862mu band with the Submillimeter Array (SMA) at sub-arcsecond spatial resolution. The observations resolved the hot molecular core into six submm continuum sources with the finest spatial resolution of 0.36''x0.25'' (~1800AU) achieved so far. Four of them located within 7800(AU)^2 comprise a proto-Trapezium system with estimated protostellar densities of 1.4x0^5 protostars/pc^3. The plethora of ~80 spectral lines allows us to study the molecular outflow(s), the core kinematics, the temperature structure of the region as well as chemical effects. The derived hot core temperatures are of the order 300K. We find interesting chemical spatial differentiations, e.g., C34S is deficient toward the hot core and is enhanced at the UCHII/hot core interface, which may be explained by temperature sensitive desorption from grains and following gas phase chemistry. The SiO(8-7) emission outlines likely two molecular outflows emanating from this hot core region. Emission from most other molecules peaks centrally on the hot core and is not dominated by any individual submm peak. Potential reasons for that are discussed. A few spectral lines that are associated with the main submm continuum source, show a velocity gradient perpendicular to the large-scale outflow. Since this velocity structure comprises three of the central protostellar sources, this is not a Keplerian disk. While the data are consistent with a gas core that may rotate and/or collapse, we cannot exclude the outflow(s) and/or nearby expanding UCHII region as possible alternative causes of this velocity pattern.

0704.0519

Eqab Rabei M.

Eqab M. Rabei and Bashar S. Ababneh

Hamilton-Jacobi Fractional Sequential Mechanics

12 pages

10.1016/j.jmaa.2008.03.011

math-ph math.MP

As a continuation of Rabei et al. work [11], the Hamilton- Jacobi partial differential equation is generalized to be applicable for systems containing fractional derivatives. The Hamilton- Jacobi function in configuration space is obtained in a similar manner to the usual mechanics. Two problems are considered to demonstrate the application of the formalism. The result found to be in exact agreement with Agrawal's formalism.

0704.0520

Tina Anna Cattolica Maiolo

Tina A.C. Maiolo, Luigi Martina, Giulio Soliani

A critical theory of quantum entanglement for the Hydrogen molecule

14 pages, 14 figures, Latex

quant-ph cond-mat.other physics.atom-ph

In this paper we investigate some entanglement properties for the Hydrogen molecule considered as a two interacting spin 1/2 (qubit) model. The entanglement related to the $H_{2}$ molecule is evaluated both using the von Neumann entropy and the Concurrence and it is compared with the corresponding quantities for the two interacting spin system. Many aspects of these functions are examinated employing in part analytical and, essentially, numerical techniques. We have compared analogous results obtained by Huang and Kais a few years ago. In this respect, some possible controversial situations are presented and discussed.

0704.0521

Frank Pollmann

E. Runge, F. Pollmann, P. Fulde

Fractionally charged excitations on frustrated lattices

submitted to the proceedings of cmt30

10.1142/S0217979207043609

cond-mat.str-el

Systems of strongly correlated fermions on certain geometrically frustrated lattices at particular filling factors support excitations with fractional charges $\pm e/2$. We calculate quantum mechanical ground states, low--lying excitations and spectral functions of finite lattices by means of numerical diagonalization. The ground state of the most thoroughfully studied case, the criss-crossed checkerboard lattice, is degenerate and shows long--range order. Static fractional charges are confined by a weak linear force, most probably leading to bound states of large spatial extent. Consequently, the quasi-particle weight is reduced, which reflects the internal dynamics of the fractionally charged excitations. By using an additional parameter, we fine--tune the system to a special point at which fractional charges are manifestly deconfined--the so--called Rokhsar--Kivelson point. For a deeper understanding of the low--energy physics of these models and for numerical advantages, several conserved quantum numbers are identified.

0704.0522

Emmanuel Latour

The BABAR Collaboration, B. Aubert, et al

Measurement of Decay Amplitudes of B -->(c cbar) Kstar with an Angular Analysis, for (c cbar)=J/psi, psi(2S) and chi_c1

Comments: 8 pages, 5 postscript figures

Phys.Rev.D76:031102,2007

10.1103/PhysRevD.76.031102

hep-ex

We perform the first three-dimensional measurement of the amplitudes of $B\to \psi(2S) K^*$ and $B\to \chi_{c1} K^*$ decays and update our previous measurement for $B\to J/\psi K^*$. We use a data sample collected with the BaBar detector at the PEP2 storage ring, corresponding to 232 million $B\bar B$ pairs. The longitudinal polarization of decays involving a $J^{PC}=1^{++}$ $\chi_{c1}$ meson is found to be larger than that with a $1^{--}$ $J/\psi$ or $\psi(2S)$ meson. No direct {\it CP}-violating charge asymmetry is observed.

0704.0523

Hyunseok Jeong

Hyunseok Jeong and Timothy C. Ralph

Quantum superpositions and entanglement of thermal states at high temperatures and their applications to quantum information processing

12 pages, 11 figures, minor corrections, to be published in Phys. Rev. A

Phys. Rev. A 76, 042103 (2007)

10.1103/PhysRevA.76.042103

quant-ph

We study characteristics of superpositions and entanglement of thermal states at high temperatures and discuss their applications to quantum information processing. We introduce thermal-state qubits and thermal-Bell states, which are a generalization of pure-state qubits and Bell states to thermal mixtures. A scheme is then presented to discriminate between the four thermal-Bell states without photon number resolving detection but with Kerr nonlinear interactions and two single-photon detectors. This enables one to perform quantum teleportation and gate operations for quantum computation with thermal-state qubits.

0704.0524

Fulvia Confortola

S. Bonaccorsi, F. Confortola, E. Mastrogiacomo

Optimal control of stochastic differential equations with dynamical boundary conditions

18 pages

10.1016/j.jmaa.2008.03.013

math.PR

In this paper we investigate the optimal control problem for a class of stochastic Cauchy evolution problem with non standard boundary dynamic and control. The model is composed by an infinite dimensional dynamical system coupled with a finite dimensional dynamics, which describes the boundary conditions of the internal system. In other terms, we are concerned with non standard boundary conditions, as the value at the boundary is governed by a different stochastic differential equation.

0704.0525

Sezgin Ayg\"un

Sezgin Aygun, Ismail Tarhan, Husnu Baysal

On the Energy-Momentum Problem in Static Einstein Universe

This submission has been withdrawn by arXiv administrators due to inappropriate text reuse from external sources

Chin.Phys.Lett.24:355-358,2007

10.1088/0256-307X/24/2/015

gr-qc

This paper has been removed by arXiv administrators because it plagiarizes gr-qc/0410004, gr-qc/0603075, and others. This paper also has excessive overlap with the following papers also written by the authors or their collaborators: gr-qc/0608111, and others.

0704.0526

Eqab Rabei M.

Eqab M. Rabei, Ibrahim M. A. Altarazi, Sami I. Muslih, Dumitru Baleanu

Fractional WKB Approximation

11 pages

math-ph hep-th math.MP

Wentzel, Kramers, Brillouin (WKB) approximation for fractional systems is investigated in this paper using the fractional calculus. In the fractional case the wave function is constructed such that the phase factor is the same as the Hamilton's principle function "S". To demonstrate our proposed approach two examples are investigated in details.

0704.0527

Bernard Piette

B.M.A.G. Piette and G.I. Probert

Towards Skyrmion Stars: Large Baryon Configurations in the Einstein-Skyrme Model

23 pages, 8 figures

Phys.Rev.D75:125023,2007

10.1103/PhysRevD.75.125023

hep-th

We investigate the large baryon number sector of the Einstein-Skyrme model as a possible model for baryon stars. Gravitating hedgehog skyrmions have been investigated previously and the existence of stable solitonic stars excluded due to energy considerations. However, in this paper we demonstrate that by generating gravitating skyrmions using rational maps, we can achieve multi-baryon bound states whilst recovering spherical symmetry in the limit where B becomes large.

0704.0528

Soung Liew

Chi Pan Chan, Soung Chang Liew, An Chan

Many-to-One Throughput Capacity of IEEE 802.11 Multi-hop Wireless Networks

cs.NI cs.IT math.IT

This paper investigates the many-to-one throughput capacity (and by symmetry, one-to-many throughput capacity) of IEEE 802.11 multi-hop networks. It has generally been assumed in prior studies that the many-to-one throughput capacity is upper-bounded by the link capacity L. Throughput capacity L is not achievable under 802.11. This paper introduces the notion of "canonical networks", which is a class of regularly-structured networks whose capacities can be analyzed more easily than unstructured networks. We show that the throughput capacity of canonical networks under 802.11 has an analytical upper bound of 3L/4 when the source nodes are two or more hops away from the sink; and simulated throughputs of 0.690L (0.740L) when the source nodes are many hops away. We conjecture that 3L/4 is also the upper bound for general networks. When all links have equal length, 2L/3 can be shown to be the upper bound for general networks. Our simulations show that 802.11 networks with random topologies operated with AODV routing can only achieve throughputs far below the upper bounds. Fortunately, by properly selecting routes near the gateway (or by properly positioning the relay nodes leading to the gateway) to fashion after the structure of canonical networks, the throughput can be improved significantly by more than 150%. Indeed, in a dense network, it is worthwhile to deactivate some of the relay nodes near the sink judiciously.

0704.0529

Gilles Santi

C. Dubois, G. Santi, I. Cuttat, C. Berthod, N. Jenkins, A. P. Petrovi\'c, A. A. Manuel, {\O}. Fischer, S. M. Kazakov, Z. Bukowski, J. Karpinski

Scanning Tunneling Spectroscopy in the Superconducting State and Vortex Cores of the beta-pyrochlore KOs2O6

5 pages, 4 figures, Revtex 4

Phys. Rev. Lett. 101, 057004 (2008)

10.1103/PhysRevLett.101.057004

cond-mat.supr-con

We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc = 9.6 K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully-gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31-40 {\AA}, in agreement with the value derived from the upper critical field Hc2. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.

0704.0530

Olaf Lechtenfeld

Olaf Lechtenfeld, Alexander D. Popov

Noncommutative Solitons in a Supersymmetric Chiral Model in 2+1 Dimensions

1+24 pages; v2: addition to Introduction and minor clarifications in Section 4, version published in JHEP

JHEP 0706:065,2007

10.1088/1126-6708/2007/06/065

hep-th

We consider a supersymmetric Bogomolny-type model in 2+1 dimensions originating from twistor string theory. By a gauge fixing this model is reduced to a modified U(n) chiral model with N<=8 supersymmetries in 2+1 dimensions. After a Moyal-type deformation of the model, we employ the dressing method to explicitly construct multi-soliton configurations on noncommutative R^{2,1} and analyze some of their properties.

0704.0531

Anastasios Petkou

Robert G. Leigh, Anastasios C. Petkou

Gravitational Duality Transformations on (A)dS4

14 pages, v2: minor clarifications, references added, v3: more references added

JHEP0711:079,2007

10.1088/1126-6708/2007/11/079

ILL-(TH)-07-02

hep-th

We discuss the implementation of electric-magnetic duality transformations in four-dimensional gravity linearized around Minkowski or (A)dS4 backgrounds. In the presence of a cosmological constant duality generically modifies the Hamiltonian, nevertheless the bulk dynamics is unchanged. We pay particular attention to the boundary terms generated by the duality transformations and discuss their implications for holography.

0704.0532

Guy Trambly De Laissardiere

Guy Trambly De Laissardi\`ere (LPTM), Didier Mayou (NEEL)

Effect of transition-metal elements on the electronic properties of quasicrystals and complex aluminides

Publication in the honor of Prof. T. Fujiwara. Editors: Y. Hatsugai, M. Arai, S. Yamamoto (2007) p. 128-144 (2007)

cond-mat.mtrl-sci

In this paper, we briefly present our work on the role of transition-metal element in electronic structure and transport properties of quasicrystals and related complex phases. Several Parts of these works have been done or initiated in collaboration with Prof. T. Fujiwara.

0704.0533

Japil Koo

J. Koo, C. Song, S. Ji, J.-S. Lee, J. Park, T.-H. Jang, C.-H. Yang, J.-H. Park, Y. H. Jeong, K.-B. Lee, T. Y. Koo, Y. J. Park, J.-Y. Kim, D. Wemeille, A. I. Goldman, G. Srajer, S. Park, S.-W. Cheong

Non-resonant and Resonant X-ray Scattering Studies on Multiferroic TbMn2O5

4 pages, 4 figures

10.1103/PhysRevLett.99.197601

cond-mat.str-el cond-mat.mtrl-sci

Comprehensive x-ray scattering studies, including resonant scattering at Mn L-edge, Tb L- and M-edges, were performed on single crystals of TbMn2O5. X-ray intensities were observed at a forbidden Bragg position in the ferroelectric phases, in addition to the lattice and the magnetic modulation peaks. Temperature dependences of their intensities and the relation between the modulation wave vectors provide direct evidences of exchange striction induced ferroelectricity. Resonant x-ray scattering results demonstrate the presence of multiple magnetic orders by exhibiting their different temperature dependences. The commensurate-to-incommensurate phase transition around 24 K is attributed to discommensuration through phase slipping of the magnetic orders in spin frustrated geometries. We proposed that the low temperature incommensurate phase consists of the commensurate magnetic domains separated by anti-phase domain walls which reduce spontaneous polarizations abruptly at the transition.

0704.0534

Juergen Horbach

Juergen Horbach, Subir K. Das, Axel Griesche, Michael-Peter Macht, Guenter Frohberg, Andreas Meyer

Self-diffusion and Interdiffusion in Al80Ni20 Melts: Simulation and Experiment

9 pages, 7 figures. Phys. Rev. B, accepted for publication

10.1103/PhysRevB.75.174304

cond-mat.dis-nn cond-mat.mtrl-sci

A combination of experimental techniques and molecular dynamics (MD) computer simulation is used to investigate the diffusion dynamics in Al80Ni20 melts. Experimentally, the self-diffusion coefficient of Ni is measured by the long-capillary (LC) method and by quasielastic neutron scattering. The LC method yields also the interdiffusion coefficient. Whereas the experiments were done in the normal liquid state, the simulations provided the determination of both self-diffusion and interdiffusion constants in the undercooled regime as well. The simulation results show good agreement with the experimental data. In the temperature range 3000 K >= T >= 715 K, the interdiffusion coefficient is larger than the self-diffusion constants. Furthermore the simulation shows that this difference becomes larger in the undercooled regime. This result can be refered to a relatively strong temperature dependence of the thermodynamic factor \Phi, which describes the thermodynamic driving force for interdiffusion. The simulations also indicate that the Darken equation is a good approximation, even in the undercooled regime. This implies that dynamic cross correlations play a minor role for the temperature range under consideration.

0704.0535

Antonio Pipino

Antonio Pipino (1,3), Thomas H. Puzia (2,4), and Francesca Matteucci (3) ((1) Astrophysics, University of Oxford, UK (2) Herzberg Institute of Astrophysics, Canada, (3) Dipartimento di Astronomia, Universita' di Trieste, Italy, (4) Space Telescope Science Institute, USA.)

The Formation of Globular Cluster Systems in Massive Elliptical Galaxies: Globular Cluster Multimodality from Radial Variation of Stellar Populations

32 pages (referee format), 9 figures, ApJ accepted

Astrophys.J.665:295-305,2007

10.1086/519546

astro-ph

The most massive elliptical galaxies show a prominent multi-modality in their globular cluster system color distributions. Understanding the mechanisms which lead to multiple globular cluster sub-populations is essential for a complete picture of massive galaxy formation. By assuming that globular cluster formation traces the total star formation and taking into account the radial variations in the composite stellar populations predicted by the Pipino & Matteucci (2004) multi-zone photo-chemical evolution code, we compute the distribution of globular cluster properties as a function of galactocentric radius. We compare our results to the spectroscopic measurements of globular clusters in nearby early-type galaxies by Puzia et al. (2006) and show that the observed multi-modality in globular cluster systems of massive ellipticals can be, at least partly, ascribed to the radial variation in the mix of stellar populations. Our model predicts the presence of a super-metal-rich population of globular clusters in the most massive elliptical galaxies, which is in very good agreement with the spectroscopic observations. Furthermore, we investigate the impact of other non-linear mechanisms that shape the metallicity distribution of globular cluster systems, in particular the role of merger-induced globular cluster formation and a non-linear color-metallicity transformation, and discuss their influence in the context of our model (abridged)

0704.0536

Guillaume Dubus

Guillaume Dubus

Binaries, microquasars and GLAST

5 pages, invited talk to appear in Proc. of the 1st GLAST Symposium, Feb 5-8, 2007, Stanford, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meegan

astro-ph

Radio and X-ray observations of the relativistic jets of microquasars show evidence for the acceleration of particles to very high energies. Signatures of non-thermal processes occurring closer in to the compact object can also be found. In addition, three binaries are now established emitters of high (> 100 MeV) and/or very high (> 100GeV) energy gamma-rays. High-energy emission can originate from a microquasar jet (accretion-powered) or from a shocked pulsar wind (rotation-powered). I discuss the impact GLAST will have in the very near future on studies of such binaries. GLAST is expected to shed new light on the link between accretion and ejection in microquasars and to enable to probe pulsar winds on small scales in rotation-powered binaries.

0704.0537

J\'er\'emy Blanc

J\'er\'emy Blanc

Linearisation of finite abelian subgroups of the Cremona group of the plane

41 pages, 2 figures, is a part of the author's PHD whose full text is available at math.AG/0610368. To appear in Groups Geom. Dyn

Groups Geom. Dyn. 3 (2009), no. 2, 215-266

10.4171/GGD/55

math.AG

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

This article gives the proof of results announced in [J. Blanc, Finite Abelian subgroups of the Cremona group of the plane, C.R. Acad. Sci. Paris, S\'er. I 344 (2007), 21-26.] and some description of automorphisms of rational surfaces. Given a finite Abelian subgroup of the Cremona group of the plane, we provide a way to decide whether it is birationally conjugate to a group of automorphisms of a minimal surface. In particular, we prove that a finite cyclic group of birational transformations of the plane is linearisable if and only if none of its non-trivial elements fix a curve of positive genus. For finite Abelian groups, there exists only one surprising exception, a group isomorphic to Z/2ZxZ/4Z, whose non-trivial elements do not fix a curve of positive genus but which is not conjugate to a group of automorphisms of a minimal rational surface. We also give some descriptions of automorphisms (not necessarily of finite order) of del Pezzo surfaces and conic bundles.

0704.0538

Marius Prelipceanu

M. Prelipceanu, O.S. Prelipceanu, O.G. Tudose, K. Grytsenko, S. Schrader

Oriented growth of pentacene films on vacuum-deposited polytetrafluoroethylene layers aligned by rubbing technique

13 pages, 9 figures, 1 table, conference

cond-mat.mtrl-sci cond-mat.soft

We investigated structure and morphology of PTFE layers deposited by vacuum process in dependence on deposition parameters: deposition rate, deposition temperature, electron activation energy and activation current. Pentacene (PnC) layers deposited on top of those PTFE films are used as a tool to demonstrate the orienting ability of the PTFE layers. The molecular structure of the PTFE films was investigated by use of infrared spectroscopy. By means of ellipsometry, values of refractive index between 1.33 and 1.36 have been obtained for PTFE films in dependence on deposition conditions. Using the cold friction technique orienting PTFE layers with unidirectional grooves are obtained. On top of these PTFE films oriented PnC layers were grown. The obtained order depends both on the PTFE layer thickness and on PnC growth temperature.

0704.0539

Thomas Royen

Thomas Royen

Integral representations for convolutions of non-central multivariate gamma distributions

12 pages

math.ST stat.TH

Three types of integral representations for the cumulative distribution functions of convolutions of non-central p-variate gamma distributions are given by integration of elementary complex functions over the p-cube Cp = (-pi,pi]x...x(-pi,pi]. In particular, the joint distribution of the diagonal elements of a generalized quadratic form XAX' with n independent normally distributed column vectors in X is obtained. For a single p-variate gamma distribution function (p-1)-variate integrals over Cp-1 are derived. The integrals are numerically more favourable than integrals obtained from the Fourier or laplace inversion formula.

0704.0540

Jinhua Jiang

Jinhua Jiang and Xin Yan

On the Achievable Rate Regions for Interference Channels with Degraded Message Sets

22 pages, 8 figures, submitted to IEEE Trans. Inform. Theory

cs.IT math.IT

The interference channel with degraded message sets (IC-DMS) refers to a communication model in which two senders attempt to communicate with their respective receivers simultaneously through a common medium, and one of the senders has complete and a priori (non-causal) knowledge about the message being transmitted by the other. A coding scheme that collectively has advantages of cooperative coding, collaborative coding, and dirty paper coding, is developed for such a channel. With resorting to this coding scheme, achievable rate regions of the IC-DMS in both discrete memoryless and Gaussian cases are derived, which, in general, include several previously known rate regions. Numerical examples for the Gaussian case demonstrate that in the high-interference-gain regime, the derived achievable rate regions offer considerable improvements over these existing results.

0704.0541

Yahya Ould Hamidoune

Y. O. Hamidoune, A.S. Llad\'o and O. Serra

On complete subsets of the cyclic group

math.NT

A subset $X$ of an abelian $G$ is said to be {\em complete} if every element of the subgroup generated by $X$ can be expressed as a nonempty sum of distinct elements from $X$. Let $A\subset \Z_n$ be such that all the elements of $A$ are coprime with $n$. Solving a conjecture of Erd\H{o}s and Heilbronn, Olson proved that $A$ is complete if $n$ is a prime and if $|A|>2\sqrt{n}.$ Recently Vu proved that there is an absolute constant $c$, such that for an arbitrary large $n$, $A$ is complete if $|A|\ge c\sqrt{n},$ and conjectured that 2 is essentially the right value of $c$. We show that $A$ is complete if $|A|> 1+2\sqrt{n-4}$, thus proving the last conjecture.

0704.0542

K Raghavan Dr.

K. N. Raghavan and Shyamashree Upadhyay

Hilbert functions of points on Schubert varieties in Orthogonal Grassmannians

latex; 73 pages; uses packages ifthen, graphicx, epsf, color; 9 figures (some in color); figures in color may not print well on a non-color printer; includes table of contents and index of definitions and notation. For version 2: reference to 0703.0637 and comments upon it added; typos corrected

math.CO math.AC math.AG

A solution is given to the following problem: how to compute the multiplicity, or more generally the Hilbert function, at a point on a Schubert variety in an orthogonal Grassmannian. Standard monomial theory is applied to translate the problem from geometry to combinatorics. The solution of the resulting combinatorial problem forms the bulk of the paper. This approach has been followed earlier to solve the same problem for the Grassmannian and the symplectic Grassmannian. As an application, we present an interpretation of the multiplicity as the number of non-intersecting lattice paths of a certain kind. Taking the Schubert variety to be of a special kind and the point to be the "identity coset," our problem specializes to a problem about Pfaffian ideals treatments of which by different methods exist in the literature. Also available in the literature is a geometric solution when the point is a "generic singularity."

0704.0543

Patrizia Romano

P. Romano (1,2), L. Sidoli (3), V. Mangano (4), S. Mereghetti (3), G. Cusumano (4) ((1) INAF-OABrera, (2) Univ.Bicocca, (3) INAF-IASF Mi, (4) INAF-IASF Pa)

Swift/XRT observes the fifth outburst of the periodic Supergiant Fast X-ray Transient IGR J11215-5952

Accepted for Publication in Astronomy and Astrophysics Letters. 5 pages, 3 figures, 2 tables

10.1051/0004-6361:20077383

astro-ph

IGR J11215-5952 is a hard X-ray transient source discovered in April 2005 with INTEGRAL and a confirmed member of the new class of High Mass X-ray Binaries, the Supergiant Fast X-ray Transients (SFXTs). Archival INTEGRAL data and RXTE observations showed that the outbursts occur with a periodicity of ~330 days. Thus, IGR J11215-5952 is the first SFXT displaying periodic outbursts, possibly related to the orbital period. We performed a Target of Opportunity observation with Swift with the main aim of monitoring the source behaviour around the time of the fifth outburst, expected on 2007 Feb 9. The source field was observed with Swift twice a day (2ks/day) starting from 4th February, 2007, until the fifth outburst, and then for ~5 ks a day afterwards, during a monitoring campaign that lasted 23 days for a total on-source exposure of ~73 ks. This is the most complete monitoring campaign of an outburst from a SFXT. The spectrum during the brightest flares is well described by an absorbed power law with a photon index of 1 and N_H~1 10^22 cm^-2. A 1-10 keV peak luminosity of ~10^36 erg s^-1 was derived (assuming 6.2 kpc, the distance of the optical counterpart). These Swift observations are a unique data-set for an outburst of a SFXT, thanks to the combination of sensitivity and time coverage, and they allowed a study of IGR J11215-5952 from outburst onset to almost quiescence. We find that the accretion phase lasts longer than previously thought on the basis of lower sensitivity instruments observing only the brightest flares. The observed phenomenology is consistent with a smoothly increasing flux triggered at the periastron passage in a wide eccentric orbit with many flares superimposed, possibly due to episodic or inhomogeneous accretion.

0704.0544

Oksana Patsahan

O.V. Patsahan, J.-M. Caillol, I.M. Mryglod

Crossover behavior in fluids with Coulomb interactions

23 pages, 8 figures

Eur. Phys. J. B 58, 449-459 (2007)

10.1140/epjb/e2007-00247-7

cond-mat.soft cond-mat.stat-mech

According to extensive experimental findings, the Ginzburg temperature $t_{G}$ for ionic fluids differs substantially from that of nonionic fluids [Schr\"oer W., Weig\"{a}rtner H. 2004 {\it Pure Appl. Chem.} {\bf 76} 19]. A theoretical investigation of this outcome is proposed here by a mean field analysis of the interplay of short and long range interactions on the value of $t_{G}$. We consider a quite general continuous charge-asymmetric model made of charged hard spheres with additional short-range interactions (without electrostatic interactions the model belongs to the same universality class as the 3D Ising model). The effective Landau-Ginzburg Hamiltonian of the full system near its gas-liquid critical point is derived from which the Ginzburg temperature is calculated as a function of the ionicity. The results obtained in this way for $t_{G}$ are in good qualitative and sufficient quantitative agreement with available experimental data.

0704.0545

Maxim Mostovoy

Maxim Mostovoy

Reply to Comment of Kenzelmann and Harris

1 page

cond-mat.str-el cond-mat.mtrl-sci

In response to the comment of Kenzelmann and Harris I show how the continuum theory of spiral multiferroics can be modified to describe general magnetic orders and discuss why the microscopic mechanism of magnetically-induced ferroelectricity usually makes such modifications unnecessary. This explains why the simple model with a single vector order parameter successfully describes thermodynamics and magnetoelectric properties of many spiral multiferroics.

0704.0546

Francesco Romeo

F. Romeo and R. De Luca

Persistent Currents in Superconducting Quantum Interference Devices

16 pages, 5 figures

Phys. Lett. A 373, 1383-1386 (2009)

10.1016/j.physleta.2009.02.013

cond-mat.mes-hall cond-mat.supr-con

Starting from the reduced dynamical model of a two-junction quantum interference device, a quantum analog of the system has been exhibited, in order to extend the well known properties of this device to the quantum regime. By finding eigenvalues of the corresponding Hamiltonian operator, the persistent currents flowing in the ring have been obtained. The resulting quantum analog of the overdamped two-junction quantum interference device can be seen as a supercurrent qubit operating in the limit of negligible capacitance and finite inductance.

0704.0547

Rachel Dudik Ms.

R. P. Dudik, J. C. Weingartner, S. Satyapal, J. Fischer, C. C. Dudley, B. O'Halloran

Mid-Infrared Fine Structure Line Ratios in Active Galactic Nuclei Observed with Spitzer IRS: Evidence for Extinction by the Torus

Accepted by ApJ

Astrophys.J.664:71-87,2007

10.1086/518685

astro-ph

We present the first systematic investigation of the [NeV] (14um/24um) and [SIII] (18um/33um) infrared line flux ratios, traditionally used to estimate the density of the ionized gas, in a sample of 41 Type 1 and Type 2 active galactic nuclei (AGNs) observed with the Infrared Spectrograph on board Spitzer. The majority of galaxies with both [NeV] lines detected have observed [NeV] line flux ratios consistent with or below the theoretical low density limit, based on calculations using currently available collision strengths and ignoring absorption and stimulated emission. We find that Type 2 AGNs have lower line flux ratios than Type 1 AGNs and that all of the galaxies with line flux ratios below the low density limit are Type 2 AGNs. We argue that differential infrared extinction to the [NeV] emitting region due to dust in the obscuring torus is responsible for the ratios below the low density limit and we suggest that the ratio may be a tracer of the inclination angle of the torus to our line of sight. Because the temperature of the gas, the amount of extinction, and the effect of absorption and stimulated emission on the line ratios are all unknown, we are not able to determine the electron densities associated with the [NeV] line flux ratios for the objects in our sample. We also find that the [SIII] emission from the galaxies in our sample is extended and originates primarily in star forming regions. Since the emission from low-ionization species is extended, any analysis using line flux ratios from such species obtained from slits of different sizes is invalid for most nearby galaxies.

0704.0548

Michel Cribier

M. Cribier (APC)

Neutrinos and Non-proliferation in Europe

Earth Moon Planets 99:331-341,2006

10.1007/s11038-006-9105-7

APC-05-180/conf

nucl-ex

Triggered by the demand of the IAEA, neutrino physicists in Europe involved with the Double Chooz experiment are studying the potential of neutrino detection to monitor nuclear reactors. In particular a new set of experiments at the ILL is planned to improve the knowledge of the neutrino spectrum emitted in the fission of 235U and 239Pu.

0704.0549

Giuseppe Mussardo

Giuseppe Mussardo

Kinks and Particles in Non-integrable Quantum Field Theories

17 pages, 8 figures, to appear in the proceedings of the XVth International Congress on Mathematical Physics, Rio de Janeiro, 6-11 August 2006

hep-th

In this talk we discuss an elementary derivation of the semi-classical spectrum of neutral particles in two field theories with kink excitations. We also show that, in the non-integrable cases, each vacuum state cannot generically support more than two stable particles, since all other neutral exitations are resonances, which will eventually decay.

0704.0550

Angela Bragaglia

Monica Tosi (1), Angela Bragaglia (1), Michele Cignoni (1,2) ((1): INAF-Osserv. Astron. Bologna (2): Astronomy Dept., Bologna Univ.)

The old open clusters Berkeley 32 and King 11

Accepted for publication on MNRAS (figs. 6 and 10 shown at degraded resolution)

Mon.Not.Roy.Astron.Soc.378:730-740,2007

10.1111/j.1365-2966.2007.11827.x

astro-ph

We have obtained CCD BVI imaging of the old open clusters Berkeley 32 and King 11. Using the synthetic colour-magnitude diagram method with three different sets of stellar evolution models of various metallicities, with and without overshooting, we have determined their age, distance, reddening, and indicative metallicity, as well as distance from the Galactic centre and height from the Galactic plane. The best parameters derived for Berkeley 32 are: subsolar metallicity (Z=0.008 represents the best choice, Z=0.006 or 0.01 are more marginally acceptable), age = 5.0-5.5 Gyr (models with overshooting; without overshooting the age is 4.2-4.4 Gyr with poorer agreement), (m-M)_0=12.4-12.6, E(B-V)=0.12-0.18 (with the lower value being more probable because it corresponds to the best metallicity), Rgc ~ 10.7-11 kpc, and |Z| ~ 231-254 pc. The best parameters for King 11 are: Z=0.01, age=3.5-4.75 Gyr, (m-M)_0=11.67-11.75, E(B-V)=1.03-1.06, Rgc ~ 9.2-10 kpc, and |Z| ~ 253-387 pc.

0704.0551

Marco Tomassini

L. Luthi, M. Tomassini, M. Giacobini, B. W. Langdon

The Genetic Programming Collaboration Network and its Communities

16 pages, 6 figures, to appear in genetic and evolutionary conference gecco 07

physics.soc-ph

Useful information about scientific collaboration structures and patterns can be inferred from computer databases of published papers. The genetic programming bibliography is the most complete reference of papers on GP\@. In addition to locating publications, it contains coauthor and coeditor relationships from which a more complete picture of the field emerges. We treat these relationships as undirected small world graphs whose study reveals the community structure of the GP collaborative social network. Automatic analysis discovers new communities and highlights new facets of them. The investigation reveals many similarities between GP and coauthorship networks in other scientific fields but also some subtle differences such as a smaller central network component and a high clustering.

0704.0552

Jozsef Vinko

J. Vinko, K. Takats

The Expanding Photosphere Method: Progress and Problems

5 pages; to appear in the AIP conference proceedings of "Supernova 1987A: 20 Years After - Supernovae and Gamma-Ray Bursters", February 19-23, 2007, Aspen, Colorado

AIP Conf.Proc.937:394-398,2007

10.1063/1.2803597

astro-ph

Distances to well-observed Type II-P SNe are determined from an updated version of the Expanding Photosphere Method (EPM), based on recent theoretical models. The new EPM distances show good agreement with other independent distances to the host galaxies without any significant systematic bias, contrary to earlier results in the literature. The accuracy of the method is comparable with that of the distance measurements for Type Ia SNe.

0704.0553

Juansher Chkareuli Levan

J.L. Chkareuli and J.G. Jejelava

Spontaneous Lorentz Violation: Non-Abelian Gauge Fields as Pseudo-Goldstone Vector Bosons

Invited talk given at Caucasian-German School and Workshop in Hadron Physics (4-7 September 2006, Tbilisi, Georgia)

Phys.Lett.B659:754-760,2008

10.1016/j.physletb.2007.11.073

hep-th hep-ph

We argue that non-Abelian gauge fields can be treated as the pseudo-Goldstone vector bosons caused by spontaneous Lorentz invariance violation (SLIV). To this end, the SLIV which evolves in a general Yang-Mills type theory with the nonlinear vector field constraint $Tr(% \boldsymbol{A}_{\mu }\boldsymbol{A}^{\mu})=\pm M^{2}$ ($M$ is a proposed SLIV scale) imposed is considered in detail. With an internal symmetry group $G$ having $D$ generators not only the pure Lorentz symmetry SO(1,3), but the larger accidental symmetry $SO(D,3D)$ of the SLIV constraint in itself appears to be spontaneously broken as well. As a result, while the pure Lorentz violation still generates only one genuine Goldstone vector boson, the accompanying pseudo-Goldstone vector bosons related to the $SO(D,3D)$ breaking also come into play in the final arrangement of the entire Goldstone vector field multiplet. Remarkably, they remain strictly massless, being protected by gauge invariance of the Yang-Mills theory involved. We show that, although this theory contains a plethora of Lorentz and $CPT$ violating couplings, they do not lead to physical SLIV effects which turn out to be strictly cancelled in all the lowest order processes considered. However, the physical Lorentz violation could appear if the internal gauge invariance were slightly broken at very small distances influenced by gravity. For the SLIV scale comparable with the Planck one the Lorentz violation could become directly observable at low energies.

0704.0554

Theodoros Gaitanos

V. Prassa, G. Ferini, T. Gaitanos, H.H. Wolter, G.A. Lalazissis, M. Di Toro

In-medium effects on particle production in heavy ion collisions

29 pages, 15 figures, accepted for publication in Nuclear Physics A

Nucl.Phys.A789:311-333,2007

10.1016/j.nuclphysa.2007.02.014

nucl-th

The effect of possible in-medium modifications of nucleon-nucleon ($NN$) cross sections on particle production is investigated in heavy ion collisions ($HIC$) at intermediate energies. In particular, using a fully covariant relativistic transport approach, we see that the density dependence of the {\it inelastic} cross sections appreciably affects the pion and kaon yields and their rapidity distributions. However, the $(\pi^{-}/\pi^{+})$- and $(K^{0}/K^{+})$-ratios depend only moderately on the in-medium behavior of the inelastic cross sections. This is particularly true for kaon yield ratios, since kaons are more uniformly produced in high density regions. Kaon potentials are also suitably evaluated in two schemes, a chiral perturbative approach and an effective meson-quark coupling method, with consistent results showing a similar repulsive contribution for $K^{+}$ and $K^{0}$. As a consequence we expect rather reduced effects on the yield ratios. We conclude that particle ratios appear to be robust observables for probing the nuclear equation of state ($EoS$) at high baryon density and, particularly, its isovector sector.

0704.0555

Liangpan Li

Liangpan Li

The Graham conjecture implies the Erdos-Turan conjecture

3 pages

math.NT

Erd\"{o}s and Tur\'{a}n once conjectured that any set $A\subset\mathbb{N}$ with $\sum_{a\in A}{1}/{a}=\infty$ should contain infinitely many progressions of arbitrary length $k\geq3$. For the two-dimensional case Graham conjectured that if $B\subset \mathbb{N}\times\mathbb{N}$ satisfies $$\sum\limits_{(x,y)\in B}\frac{1}{x^2+y^2}=\infty,$$ then for any $s\geq2$, $B$ contains an $s\times s$ axes-parallel grid. In this paper it is shown that if the Graham conjecture is true for some $s\geq2$, then the Erd\"{o}s-Tur\'{a}n conjecture is true for $k=2s-1$.

0704.0556

Christopher Jesudason Prof

Christopher G Jesudason

Effective conservation of energy and momentum algorithm using switching potentials suitable for molecular dynamics simulation of thermodynamical systems

8 pages, Submitted to International Conference on Dynamical Systems and Applications, Atlanta, Georgia, USA (29 May -3 June, 2007)

physics.comp-ph physics.chem-ph

During a crossover via a switching mechanism from one 2-body potential to another as might be applied in modeling (chemical) reactions in the vicinity of bond formation, energy violations would occur due to finite step size which determines the trajectory of the particles relative to the potential interactions of the unbonded state by numerical (e.g. Verlet) integration. This problem is overcome by an algorithm which preserves the coordinates of the system for each move, but corrects for energy discrepancies by ensuring both energy and momentum conservation in the dynamics. The algorithm is tested for a hysteresis loop reaction model with an without the implementation of the algorithm. The tests involve checking the rate of energy flow out of the MD simulation box; in the equilibrium state, no net rate of flows within experimental error should be observed. The temperature and pressure of the box should also be invariant within the range of fluctuation of these quantities. It is demonstrated that the algorithm satisfies these criteria.

0704.0557

Ryszard Szczerba

R. Szczerba, M.R. Schmidt, M. Pulecka

Mixed chemistry phenomenon during late stages of stellar evolution

8 pages, 4 figures, Baltic Astronomy in press

astro-ph

We discuss phenomenon of simultaneous presence of O- and C-based material in surroundings of evolutionary advanced stars. We concentrate on silicate carbon stars and present observations that directly confirm the binary model scenario for them. We discuss also class of C-stars with OH emission detected, to which some [WR] planetary nebulae do belong.

0704.0558

Andreas H\"oring

Andreas H\"oring

M-regularity of the Fano surface

5 pages, changed metadata

math.AG

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Let $(A,\Theta)$ be a principally polarised abelian variety, and let Y be a subvariety. Pareschi and Popa conjectured that Y has minimal cohomology class if and only if the structure sheaf of Y satisfies a property that they call M-regularity. Let now X be a smooth cubic threefold. By a classical result due to Clemens and Griffiths, its intermediate Jacobian J(X) is a principally polarised abelian variety; furthermore the Fano surface of lines on X can be embedded in J(X) and has minimal cohomology class. In this short note we show that its structure sheaf is M-regular.

0704.0559

Josip Trampetic Dr.

Josip Trampetic

Signal for space-time noncommutativity: the Z -> gamma gamma decay in the renormalizable gauge sector of the theta-expanded NCSM

12 pages; 2 figures, conferences

SFINA1:379-390,2007

hep-ph

We propose the Z -> gamma gamma decay, a process strictly forbidden in the standard model, as a signal suitable for the search of noncommutativity of coordinates at very short distances. We compute the Z -> gamma gamma partial widthin the framework of the recently proposed renormalizable gauge sector of the noncommutative standard model. The one-loop renormalizability is obtained for the model containing the usual six representations of matter fields of the first generation. Even more, the noncommutative part is finite or free of divergences, showing that perhaps new interaction symmetry exists in the noncommutative gauge sector of the model. Discovery of such symmetry would be of tremendous importance in further search for the violation of the Lorentz invariance at very high energies. Experimental possibilities of Z -> gamma gamma decay are analyzed and a firm bound to the scale of the noncommutativity parameter is set around 1 TeV.

0704.0560

Danyal Winters

D.F.A. Winters, M. Vogel, D.M. Segal, R.C. Thompson and W. Noertershaeuser

Laser spectroscopy of hyperfine structure in highly-charged ions: a test of QED at high fields

5 pages, 1 figure, 1 table. accepted for Canadian Journal of Physics (2006)

10.1139/P07-023

physics.atom-ph physics.gen-ph

An overview is presented of laser spectroscopy experiments with cold, trapped, highly-charged ions, which will be performed at the HITRAP facility at GSI in Darmstadt (Germany). These high-resolution measurements of ground state hyperfine splittings will be three orders of magnitude more precise than previous measurements. Moreover, from a comparison of measurements of the hyperfine splittings in hydrogen- and lithium-like ions of the same isotope, QED effects at high electromagnetic fields can be determined within a few percent. Several candidate ions suited for these laser spectroscopy studies are presented.

0704.0561

Jorge Berger

Jorge Berger

Confinement into a state with persistent current by thermal quenching of loop of Josephson junctions

Physica C 468, 294 (2008)

10.1016/j.physc.2007.08.022

cond-mat.supr-con cond-mat.stat-mech

We study a loop of Josephson junctions that is quenched through its critical temperature. For three or more junctions, symmetry breaking states can be achieved without thermal activation, in spite of the fact that the relaxation time is practically constant when the critical temperature is approached from above. The probability for these states decreases with quenching time, but the dependence is not allometric. For large number of junctions, cooling does not have to be fast. For this case, we evaluate the standard deviation of the induced flux. Our results are consistent with the available experimental data.

0704.0562

Nathalie Picque

Julien Mandon (PPM), Guy Guelachvili (PPM), Nathalie Picqu\'e (PPM)

Frequency modulation Fourier transform spectroscopy

Optics Letters in press, in press (2007) in press

Optics Letters 32, 15 (2007) 2206-2208

physics.optics

A new method, FM-FTS, combining Frequency Modulation heterodyne laser spectroscopy and Fourier Transform Spectroscopy is presented. It provides simultaneous sensitive measurement of absorption and dispersion profiles with broadband spectral coverage capabilities. Experimental demonstration is made on the overtone spectrum of C2H2 in the 1.5 $\mu$m region.

0704.0563

Ignazio Licata

Ignazio Licata

Universe Without Singularities. A Group Approach to De Sitter Cosmology

13 pages

Electron.J.Theor.Phys.3:211-224,2006

physics.gen-ph

In the last years the traditional scenario of Big Bang has been deeply modified by the study of the quantum features of the Universe evolution, proposing again the problem of using local physical laws on cosmic scale, with particular regard to the cosmological constant role. The group extention method shows that the De Sitter group univocally generalizes the Poincare group, formally justifies the cosmological constant use and suggests a new interpretation for Hartle-Hawking boundary conditions in Quantum Cosmology.

0704.0564

Cyril Levy

D. Essouabri, B. Iochum, C. Levy and A. Sitarz

Spectral action on noncommutative torus

57 pages

published in Journal of Noncommutative Geometry, 2 (2008), 53-123

hep-th math-ph math.MP

The spectral action on noncommutative torus is obtained, using a Chamseddine--Connes formula via computations of zeta functions. The importance of a Diophantine condition is outlined. Several results on holomorphic continuation of series of holomorphic functions are obtained in this context.

0704.0565

Apostolos Damialis

Apostolos Damialis

The Lifshitz-Slyozov-Wagner equation for reaction-controlled kinetics

15 pages, LaTeX; minor revision, change of title

Proc. R. Soc. Edinb. A 140 (2010) 273-289

10.1017/S0308210508000656

math.AP

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

We rigorously derive a weak form of the Lifshitz-Slyozov-Wagner equation as the homogenization limit of a Stefan-type problem describing reaction-controlled coarsening of a large number of small spherical particles. Moreover, we deduce that the effective mean-field description holds true in the particular limit of vanishing surface-area density of particles.

0704.0566

Hajime Tsuji

Hajime Tsuji

Canonical singular hermitian metrics on relative canonical bundles

Correction on the proof of Lemma 3.2 and Corollary 3.4

math.AG math.CV

We introduce a new class of canonical AZD's (called the supercanonical AZD's) on the canonical bundles of smooth projective varieties with pseudoeffective canonical classes. We study the variation of the supercanonical AZD $\hat{h}_{can}$ under projective deformations and give a new proof of the invariance of plurigenera.

0704.0567

Martin Keller-Ressel

Martin Keller-Ressel, Thomas Steiner

Yield Curve Shapes and the Asymptotic Short Rate Distribution in Affine One-Factor Models

q-fin.PR math.PR

We consider a model for interest rates, where the short rate is given by a time-homogenous, one-dimensional affine process in the sense of Duffie, Filipovic and Schachermayer. We show that in such a model yield curves can only be normal, inverse or humped (i.e. endowed with a single local maximum). Each case can be characterized by simple conditions on the present short rate. We give conditions under which the short rate process will converge to a limit distribution and describe the limit distribution in terms of its cumulant generating function. We apply our results to the Vasicek model, the CIR model, a CIR model with added jumps and a model of Ornstein-Uhlenbeck type.

0704.0568

Marius Prelipceanu

M.Prelipceanu, O.S. Prelipceanu, O.G. Tudose, S. Schrader

Thermally Stimulated Luminescence and Current in new heterocyclic materials for Organic field transistors and organic light emitting diodes

9 pages, 7 figures, Published in Abstract Book of 7th International Conference on Physics of Advanced Materials, ICPAM7, June 2004, Iasi, Romania

cond-mat.other cond-mat.mtrl-sci

The present work is focused on theoretical and experimental study of localised levels in organic materials suitable for light-emitting devices and field effect transistors by means of thermal techniques. In our work we focused on low molecular compounds as well as on polymers, especially of two classes of materials: oxadiazoles and quinoxalines. Both organic compounds are well know as electron transport materials in OLEDs.

0704.0569

Jean-Baptiste Salmon

P. Laval, N. Lisai, J.-B. Salmon, M. Joanicot

A microfluidic device based on droplet storage for screening solubility diagrams

cond-mat.soft

This work describes a new microfluidic device developed for rapid screening of solubility diagrams. In several parallel channels, hundreds of nanoliter-volume droplets of a given solution are first stored with a gradual variation in the solute concentration. Then, the application of a temperature gradient along these channels enables us to read directly and quantitatively phase diagrams, concentration vs. temperature. We show, using a solution of adipic acid, that we can measure ten points of the solubility curve in less than 1 hr and with only 250 $\mu$L of solution.

0704.0570

Susanne Viefers

Hans Hansson, Chia-Chen Chang, Jainendra Jain, and Susanne Viefers

Composite fermion wave functions as conformal field theory correlators

26 pages, 3 figures

10.1103/PhysRevB.76.075347

cond-mat.mes-hall cond-mat.str-el

It is known that a subset of fractional quantum Hall wave functions has been expressed as conformal field theory (CFT) correlators, notably the Laughlin wave function at filling factor $\nu=1/m$ ($m$ odd) and its quasiholes, and the Pfaffian wave function at $\nu=1/2$ and its quasiholes. We develop a general scheme for constructing composite-fermion (CF) wave functions from conformal field theory. Quasiparticles at $\nu=1/m$ are created by inserting anyonic vertex operators, $P_{\frac{1}{m}}(z)$, that replace a subset of the electron operators in the correlator. The one-quasiparticle wave function is identical to the corresponding CF wave function, and the two-quasiparticle wave function has correct fractional charge and statistics and is numerically almost identical to the corresponding CF wave function. We further show how to exactly represent the CF wavefunctions in the Jain series $\nu = s/(2sp+1)$ as the CFT correlators of a new type of fermionic vertex operators, $V_{p,n}(z)$, constructed from $n$ free compactified bosons; these operators provide the CFT representation of composite fermions carrying $2p$ flux quanta in the $n^{\rm th}$ CF Landau level. We also construct the corresponding quasiparticle- and quasihole operators and argue that they have the expected fractional charge and statistics. For filling fractions 2/5 and 3/7 we show that the chiral CFTs that describe the bulk wave functions are identical to those given by Wen's general classification of quantum Hall states in terms of $K$-matrices and $l$- and $t$-vectors, and we propose that to be generally true. Our results suggest a general procedure for constructing quasiparticle wave functions for other fractional Hall states, as well as for constructing ground states at filling fractions not contained in the principal Jain series.

0704.0571

Gianluca Cavoto

Gianluca Cavoto

$\Bz\to\pip\pim\piz$ Time Dependent Dalitz analysis at BaBar

Proceedings CKM Workshop 2006 in Nagoya, 5 pages, 3 figures

hep-ex

I present here results of a time-dependent analysis of the Dalitz structure of neutral $B$ meson decays to $\pip\pim\piz$ from a dataset of 346 million $B \bar B$ pairs collected at the $\Upsilon(4S)$ center of mass energy by the BaBar detector at the SLAC PEP-II $e^+e^-$ accelerator. No significant CP violation effects are observed and 68% confidence interval is derived on the weak angle $\alpha$ to be [75$^o$,152$^o$]

0704.0572

Marius Prelipceanu

O.S. Prelipceanu, M. Prelipceanu, O.G. Tudose, B. Grimm, S. Schrader

New Organic thermally stable materials for optoelectronics devices - A linear spectroscopy study

7 pages, 12 figures, 1 table, Published in Abstract Book of 7th International Conference on Physics of Advanced Materials, ICPAM7, June 2004,Iasi - Romania

cond-mat.other cond-mat.mtrl-sci

Thermally stable polymers have attracted a lot of interest due to their potential use as the active component in electronic, optical and optoelectronic applications, such as light-emitting diodes, light emitting electrochemical cells, photodiodes, photovoltaic cells, field effect transistors, optocouplers and optically pumped lasers in solution and solid state.We report results of investigations into the use of thermal treatment of poly(p-phenylene vinylene) (PPV) films grown on a variety of substrates (quartz and glass). Film thickness, morphology and structural properties were investigated by a range of techniques in particular: atomic force microscope - AFM, DEKTAK method, Ellipsometry and UV-VIS spectroscopy.

0704.0573

Ramazan Sever

Sameer M. Ikhdair and Ramazan Sever

Elativistic treatment in}$D$ - Dimensions to a spin-zero particle with noncentral equal scalar and vector ring-shaped Kratzer potential

20 pages

quant-ph

The Klein-Gordon equation in D-dimensions for a recently proposed Kratzer potential plus ring-shaped potential is solved analytically by means of the conventional Nikiforov-Uvarov method. The exact energy bound-states and the corresponding wave functions of the Klein-Gordon are obtained in the presence of the noncentral equal scalar and vector potentials. The results obtained in this work are more general and can be reduced to the standard forms in three-dimensions given by other works.

0704.0574

Suzanne Aigrain

Suzanne Aigrain (IoA Cambridge, University of Exeter) and Frederic Pont (Geneva Observatory)

On the potential of transit surveys in star clusters: Impact of correlated noise and radial velocity follow-up

14 pages, 2 figures, accepted for publication in MNRAS

Mon.Not.Roy.Astron.Soc.378:741-752,2007

10.1111/j.1365-2966.2007.11823.x

astro-ph

We present an extension of the formalism recently proposed by Pepper & Gaudi to evaluate the yield of transit surveys in homogeneous stellar systems, incorporating the impact of correlated noise on transit time-scales on the detectability of transits, and simultaneously incorporating the magnitude limits imposed by the need for radial velocity follow-up of transit candidates. New expressions are derived for the different contributions to the noise budget on transit time-scales and the least-squares detection statistic for box-shaped transits, and their behaviour as a function of stellar mass is re-examined. Correlated noise that is constant with apparent stellar magnitude implies a steep decrease in detection probability at the high mass end which, when considered jointly with the radial velocity requirements, can severely limit the potential of otherwise promising surveys in star clusters. However, we find that small-aperture, wide field surveys may detect hot Neptunes whose radial velocity signal can be measured with present-day instrumentation in very nearby (<100 pc) clusters.

0704.0575

Alexandre C. Tort

F C Santos, V Soares and A C Tort

A non-perturbative proof of Bertrand's theorem

Latex file plus one eps figure

physics.class-ph

We discuss an alternative non-perturbative proof of Bertrand's theorem that leads in a concise way directly to the two allowed fields: the newtonian and the isotropic harmonic oscillator central fields.

0704.0576

Wenyuan Cui

Wen-Yuan Cui (1,2,3), D. N. Cui (1), Y. S. Du (1), B. Zhang (1)((1) Department of Physics, Hebei Normal University, China, (2) National Astronomical observatories, Chinese Academy of Sciences, China, (3) Graduate School of the Chinese Academy of Sciences, China)

Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007: a New s- and r-Process Paradigm

4 pages, 3 figures, paper accepted for publication in Chinese Physics letters

Chin.Phys.Lett.24:1417-1421,2007

10.1088/0256-307X/24/5/081

astro-ph

The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity [Fe/H] $=-2.0$, which is just at the upper limit of the metallicity for the observed double-enhanced stars. Using a parametric model, we find that almost all s-elements were made in a single neutron exposure. This star should be a member of a post-common-envelope binary. After the s-process material has experienced only one neutron exposure in the nucleosynthesis region and is dredged-up to its envelope, the AGB evolution is terminated by the onset of common-envelope evolution. Based on the high radial-velocity of HE 1305-0007, we speculate that the star could be a runaway star from a binary system, in which the AIC event has occurred and produced the r-process elements.

0704.0577

Xu Wei-shui

Wei-shui Xu and Ding-fang Zeng

Membrane in M5-branes Background

15 pages, typos corrected

JHEP 0705:095,2007

10.1088/1126-6708/2007/05/095

hep-th

In this paper, we investigate the properties of a membrane in the M5-brane background. Through solving the classical equations of motion of the membrane, we can understand the classical dynamics of the membrane in this background.

0704.0578

Dario Del Moro

Dario Del Moro, Silvia Giordano, Francesco Berrilli

3D photospheric velocity field of a Supergranular cell

7 pages, submitted to A&A, referee's comments included

10.1051/0004-6361:20077595

astro-ph

We investigate the plasma flow properties inside a Supergranular (SG) cell, in particular its interaction with small scale magnetic field structures. The SG cell has been identified using the magnetic network (CaII wing brightness) as proxy, applying the Two-Level Structure Tracking (TST) to high spatial, spectral and temporal resolution observations obtained by IBIS. The full 3D velocity vector field for the SG has been reconstructed at two different photospheric heights. In order to strengthen our findings, we also computed the mean radial flow of the SG by means of cork tracing. We also studied the behaviour of the horizontal and Line of Sight plasma flow cospatial with cluster of bright CaII structures of magnetic origin to better understand the interaction between photospheric convection and small scale magnetic features. The SG cell we investigated seems to be organized with an almost radial flow from its centre to the border. The large scale divergence structure is probably created by a compact region of constant up-flow close to the cell centre. On the edge of the SG, isolated regions of strong convergent flow are nearby or cospatial with extended clusters of bright CaII wing features forming the knots of the magnetic network.

0704.0579

Massimo Ramella

M. Ramella, A. Biviano, A. Pisani, J. Varela, D. Bettoni, W.J. Couch, M. D'Onofrio, A. Dressler, G. Fasano, P. Kjaergaard, M. Moles, E. Pignatelli, B.M. Poggianti

Substructures in WINGS clusters

A&A accepted - figure 6 is available from http://adlibitum.oats.inaf.it/ramella/WINGSfigs

10.1051/0004-6361:20077245

astro-ph

We search for and characterize substructures in the projected distribution of galaxies observed in the wide field CCD images of the 77 nearby clusters of the WIde-field Nearby Galaxy-cluster Survey (WINGS). This sample is complete in X-ray flux in the redshift range 0.04<z<0.07. We search for substructures in WINGS clusters with DEDICA, an adaptive-kernel procedure. We test the procedure on Monte-Carlo simulations of the observed frames and determine the reliability for the detected structures. DEDICA identifies at least one reliable structure in the field of 55 clusters. 40 of these clusters have a total of 69 substructures at the same redshift of the cluster (redshift estimates of substructures are from color-magnitude diagrams). The fraction of clusters with subclusters (73%) is higher than in most studies. The presence of subclusters affects the relative luminosities of the brightest cluster galaxies (BCGs). Down to L ~ 10^11.2 L_Sun, our observed differential distribution of subcluster luminosities is consistent with the theoretical prediction of the differential mass function of substructures in cosmological simulations.

0704.0580

Stefanie Russ

Stefanie Russ, Armin Bunde

Ising-like dynamics and frozen states in systems of ultrafine magnetic particles

5 pages, 6 figures. to appear in Phys. Rev. B

10.1103/PhysRevB.75.174445

cond-mat.dis-nn cond-mat.stat-mech

We use Monte-Carlo simulations to study aging phenomena and the occurence of spinglass phases in systems of single-domain ferromagnetic nanoparticles under the combined influence of dipolar interaction and anisotropy energy, for different combinations of positional and orientational disorder. We find that the magnetic moments oriente themselves preferably parallel to their anisotropy axes and changes of the total magnetization are solely achieved by 180 degree flips of the magnetic moments, as in Ising systems. Since the dipolar interaction favorizes the formation of antiparallel chain-like structures, antiparallel chain-like patterns are frozen in at low temperatures, leading to aging phenomena characteristic for spin-glasses. Contrary to the intuition, these aging effects are more pronounced in ordered than in disordered structures.

0704.0581

Thomas Michael Keller

Thomas Michael Keller

Counting characters in linear group actions

math.RT math.GR

Let $G$ be a finite group and $V$ be a finite $G$--module. We present upper bounds for the cardinalities of certain subsets of $\Irr(GV)$, such as the set of those $\chi\in\Irr(GV)$ such that, for a fixed $v\in V$, the restriction of $\chi$ to $<v>$ is not a multiple of the regular character of $<v>$. These results might be useful in attacking the non--coprime $k(GV)$--problem.

0704.0582

Christof Kuelske

C. Kuelske, E. Orlandi

Continuous interfaces with disorder: Even strong pinning is too weak in 2 dimensions

8 pages

math.PR math-ph math.MP

We consider statistical mechanics models of continuous height effective interfaces in the presence of a delta-pinning at height zero. There is a detailed mathematical understanding of the depinning transition in 2 dimensions without disorder. Then the variance of the interface height w.r.t. the Gibbs measure stays bounded uniformly in the volume for any positive pinning force and diverges like the logarithm of the pinning force when it tends to zero. How does the presence of a quenched disorder term in the Hamiltonian modify this transition? We show that an arbitarily weak random field term is enough to beat an arbitrarily strong delta-pinning in 2 dimensions and will cause delocalization. The proof is based on a rigorous lower bound for the overlap between local magnetizations and random fields in finite volume. In 2 dimensions it implies growth faster than the volume which is a contradiction to localization. We also derive a simple complementary inequality which shows that in higher dimensions the fraction of pinned sites converges to one when the pinning force tends to infinity.

0704.0583

Wilhelm Winter

Marius Dadarlat, Wilhelm Winter

On the KK-theory of strongly self-absorbing C*-algebras

12 pages

math.OA math.KT

Let $\Dh$ and $A$ be unital and separable $C^{*}$-algebras; let $\Dh$ be strongly self-absorbing. It is known that any two unital $^*$-homomorphisms from $\Dh$ to $A \otimes \Dh$ are approximately unitarily equivalent. We show that, if $\Dh$ is also $K_{1}$-injective, they are even asymptotically unitarily equivalent. This in particular implies that any unital endomorphism of $\Dh$ is asymptotically inner. Moreover, the space of automorphisms of $\Dh$ is compactly-contractible (in the point-norm topology) in the sense that for any compact Hausdorff space $X$, the set of homotopy classes $[X,\Aut(\Dh)]$ reduces to a point. The respective statement holds for the space of unital endomorphisms of $\Dh$. As an application, we give a description of the Kasparov group $KK(\Dh, A\ot \Dh)$ in terms of $^*$-homomorphisms and asymptotic unitary equivalence. Along the way, we show that the Kasparov group $KK(\Dh, A\ot \Dh)$ is isomorphic to $K_0(A\ot \Dh)$.

0704.0584

Varese Tim\'oteo

V.S. Timoteo and C.L. Lima

Effective interactions from q-deformed inspired transformations

Physics Letters B 635 (2006) 168

10.1590/S0103-97332007000100022

nucl-th

From the mass term for the transformed quark fields, we obtain effective contact interactions of the NJL type. The parameters of the model that maps a system of non-interacting transformed fields into quarks interacting via NJL contact terms are discussed.

0704.0585

Marcin Sadowski

M.L. Sadowski, G. Martinez, M. Potemski, C. Berger, W.A. de Heer

Magnetospectroscopy of epitaxial few-layer graphene

Invited short review to appear in a special issue of Solid State Communications

10.1016/j.ssc.2007.03.050

cond-mat.mtrl-sci cond-mat.mes-hall

The inter-Landau level transitions observed in far-infrared transmission experiments on few-layer graphene samples show a behaviour characteristic of the linear dispersion expected in graphene. This behaviour persists in relatively thick samples, and is qualitatively different from that of thin samples of bulk graphite.

0704.0586

Simone Bianchi

S. Bianchi, and R. Schneider

Dust Formation and Survival in Supernova Ejecta

MNRAS accepted

Mon.Not.Roy.Astron.Soc.378:973-982,2007

10.1111/j.1365-2966.2007.11829.x

astro-ph

The presence of dust at high redshift requires efficient condensation of grains in SN ejecta, in accordance with current theoretical models. Yet, observations of the few well studied SNe and SN remnants imply condensation efficiencies which are about two orders of magnitude smaller. Motivated by this tension, we have (i) revisited the model of Todini & Ferrara (2001) for dust formation in the ejecta of core collapse SNe and (ii) followed, for the first time, the evolution of newly condensed grains from the time of formation to their survival - through the passage of the reverse shock - in the SN remnant. We find that 0.1 - 0.6 M_sun of dust form in the ejecta of 12 - 40 M_sun stellar progenitors. Depending on the density of the surrounding ISM, between 2-20% of the initial dust mass survives the passage of the reverse shock, on time-scales of about 4-8 x 10^4 yr from the stellar explosion. Sputtering by the hot gas induces a shift of the dust size distribution towards smaller grains. The resulting dust extinction curve shows a good agreement with that derived by observations of a reddened QSO at z =6.2. Stochastic heating of small grains leads to a wide distribution of dust temperatures. This supports the idea that large amounts (~ 0.1 M_sun) of cold dust (T ~ 40K) can be present in SN remnants, without being in conflict with the observed IR emission.

0704.0587

Emmanuel Trizac

E. Trizac and G. Tellez

Preferential interaction coefficient for nucleic acids and other cylindrical poly-ions

Macromolecules 40, 1305 (2007)

10.1021/ma061497l

cond-mat.soft cond-mat.stat-mech

The thermodynamics of nucleic acid processes is heavily affected by the electric double-layer of micro-ions around the polyions. We focus here on the Coulombic contribution to the salt-polyelectrolyte preferential interaction (Donnan) coefficient and we report extremely accurate analytical expressions valid in the range of low salt concentration (when polyion radius is smaller than the Debye length). The analysis is performed at Poisson-Boltzmann level, in cylindrical geometry, with emphasis on highly charged poly-ions (beyond ``counter-ion condensation''). The results hold for any electrolyte of the form $z_-$:$z_+$. We also obtain a remarkably accurate expression for the electric potential in the vicinity of the poly-ion.

0704.0588

Fumio Hiai

F. Hiai and D. Petz

A new approach to mutual information

14 pages

math.PR math.ST stat.TH

A new expression as a certain asymptotic limit via "discrete micro-states" of permutations is provided to the mutual information of both continuous and discrete random variables.

0704.0589

Wei-Xing Zhou

Wei-Xing Zhou (ECUST), Didier Sornette (ETH Zurich)

Analysis of the real estate market in Las Vegas: Bubble, seasonal patterns, and prediction of the CSW indexes

24 Elsart pages including 13 pages and 1 table

Physica A 387 (1), 243-260 (2008)

10.1016/j.physa.2007.08.059

q-fin.GN physics.soc-ph q-fin.ST

We analyze 27 house price indexes of Las Vegas from Jun. 1983 to Mar. 2005, corresponding to 27 different zip codes. These analyses confirm the existence of a real-estate bubble, defined as a price acceleration faster than exponential, which is found however to be confined to a rather limited time interval in the recent past from approximately 2003 to mid-2004 and has progressively transformed into a more normal growth rate comparable to pre-bubble levels in 2005. There has been no bubble till 2002 except for a medium-sized surge in 1990. In addition, we have identified a strong yearly periodicity which provides a good potential for fine-tuned prediction from month to month. A monthly monitoring using a model that we have developed could confirm, by testing the intra-year structure, if indeed the market has returned to ``normal'' or if more turbulence is expected ahead. We predict the evolution of the indexes one year ahead, which is validated with new data up to Sep. 2006. The present analysis demonstrates the existence of very significant variations at the local scale, in the sense that the bubble in Las Vegas seems to have preceded the more global USA bubble and has ended approximately two years earlier (mid 2004 for Las Vegas compared with mid-2006 for the whole of the USA).

0704.0590

Rachit Agarwal

Rachit Agarwal, Ralf Koetter and Emanuel Popovici

A Low Complexity Algorithm and Architecture for Systematic Encoding of Hermitian Codes

5 Pages, Accepted in IEEE International Symposium on Information Theory ISIT 2007

10.1109/ISIT.2007.4557408

cs.IT math.IT

We present an algorithm for systematic encoding of Hermitian codes. For a Hermitian code defined over GF(q^2), the proposed algorithm achieves a run time complexity of O(q^2) and is suitable for VLSI implementation. The encoder architecture uses as main blocks q varying-rate Reed-Solomon encoders and achieves a space complexity of O(q^2) in terms of finite field multipliers and memory elements.

0704.0591

Minoru Nohara

N. Takeshita, S. Takashima, C. Terakura, H. Nishikubo, S. Miyasaka, M. Nohara, Y. Tokura, and H. Takagi

Quantum criticality and disorder in the antiferromagnetic critical point of NiS$_{2}$ pyrite

4 pages

cond-mat.str-el

A quantum critical point (QCP) between the antiferromagnetic and the paramagnetic phases was realized by applying a hydrostatic pressure of ~ 7 GPa on single crystals of NiS_{2} pyrite with a low residual resistivity, rho_{0}, of 0.5 mu-Omega-cm. We found that the critical behavior of the resistivity, rho, in this clean system contrasts sharply with those observed in its disordered analogue, NiS_{2-x}Se_{x} solid-solution, demonstrating the unexpectedly drastic effect of disorder on the quantum criticality. Over a whole paramagnetic region investigated up to P = 9 GPa, a crossover temperature, defined as the onset of T^{2} dependence of rho, an indication of Fermi liquid, was suppressed to a substantially low temperature T sim 2 K and, instead, a non Fermi liquid behavior of rho, T^{3/2}-dependence, robustly showed up.

0704.0592

Marcin Syperek

M. Syperek, D. R. Yakovlev, A. Greilich, J. Misiewicz, M. Bayer, D. Reuter, and A. D. Wieck

Spin coherence of holes in GaAs/AlGaAs quantum wells

5 pages, 4 figures in PostScript format

10.1103/PhysRevLett.99.187401

cond-mat.other

The carrier spin coherence in a p-doped GaAs/(Al,Ga)As quantum well with a diluted hole gas has been studied by picosecond pump-probe Kerr rotation with an in-plane magnetic field. For resonant optical excitation of the positively charged exciton the spin precession shows two types of oscillations. Fast oscillating electron spin beats decay with the radiative lifetime of the charged exciton of 50 ps. Long lived spin coherence of the holes with dephasing times up to 650 ps. The spin dephasing time as well as the in-plane hole g factor show strong temperature dependence, underlining the importance of hole localization at cryogenic temperatures.

0704.0593

J\"urgen K\"astel

J\"urgen K\"astel, Michael Fleischhauer, Gediminas Juzeli\=unas

Local-field effects in radiatively broadened magneto-dielectric media: negative refraction and absorption reduction

6 pages, 1 figure

cond-mat.other physics.optics quant-ph

We give a microscopic derivation of the Clausius-Mossotti relations for a homogeneous and isotropic magneto-dielectric medium consisting of radiatively broadened atomic oscillators. To this end the diagram series of electromagnetic propagators is calculated exactly for an infinite bi-cubic lattice of dielectric and magnetic dipoles for a lattice constant small compared to the resonance wavelength $\lambda$. Modifications of transition frequencies and linewidth of the elementary oscillators are taken into account in a selfconsistent way by a proper incorporation of the singular self-interaction terms. We show that in radiatively broadened media sufficiently close to the free-space resonance the real part of the index of refraction approaches the value -2 in the limit of $\rho \lambda^3 \gg 1$, where $\rho$ is the number density of scatterers. Since at the same time the imaginary part vanishes as $1/\rho$ local field effects can have important consequences for realizing low-loss negative index materials.

0704.0594

Jan Timmermans

The DELPHI Collaboration, J. Abdallah, et al

Search for a fourth generation b'-quark at LEP-II at sqrt{s}=196-209 GeV

26 pages, 12 figures, Accepted by Eur. Phys. J. C

Eur.Phys.J.C50:507-518,2007

10.1140/epjc/s10052-007-0273-z

CERN-PH-EP/2006-023

hep-ex

A search for the pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb^{-1}. No evidence for a signal was found. Upper limits on BR(b' -> bZ) and BR(b' -> cW) were obtained for b' masses ranging from 96 to 103 GeV/c^2. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of R_{CKM}=|V_{cb'}/V_{tb'}V_{tb}|, where V_{cb'}, V_{tb'} and V_{tb} are elements of the extended CKM matrix.

0704.0595

Fernando Dobarro

Fernando Dobarro, Bulent Unal

About curvature, conformal metrics and warped products

32 pages, 3 figures

J.Phys.A40:13907-13930,2007

10.1088/1751-8113/40/46/006

math.DG gr-qc hep-th math-ph math.AP math.MP

We consider the curvature of a family of warped products of two pseduo-Riemannian manifolds $(B,g_B)$ and $(F,g_F)$ furnished with metrics of the form $c^{2}g_B \oplus w^2 g_F$ and, in particular, of the type $w^{2 \mu}g_B \oplus w^2 g_F$, where $c, w \colon B \to (0,\infty)$ are smooth functions and $\mu$ is a real parameter. We obtain suitable expressions for the Ricci tensor and scalar curvature of such products that allow us to establish results about the existence of Einstein or constant scalar curvature structures in these categories. If $(B,g_B)$ is Riemannian, the latter question involves nonlinear elliptic partial differential equations with concave-convex nonlinearities and singular partial differential equations of the Lichnerowicz-York type among others.

0704.0596

Andrzej Derdzinski

Andrzej Derdzinski (Ohio State University), Witold Roter (Wroclaw University of Technology)

The local structure of conformally symmetric manifolds

12 pages

Bulletin of the Belgian Mathematical Society - Simon Stevin 16 (2009), no. 1, 117-128

math.DG

This is a final step in a local classification of pseudo-Riemannian manifolds with parallel Weyl tensor that are not conformally flat or locally symmetric.

0704.0597

Jan Timmermans

The DELPHI Collaboration, J. Abdallah, et al

Investigation of Colour Reconnection in WW Events with the DELPHI detector at LEP-2

39 pages, 18 figures, Accepted by Eur. Phys. J. C

Eur.Phys.J.C51:249-269,2007

10.1140/epjc/s10052-007-0304-9

CERN-PH-EP/2006-037

hep-ex

In the reaction e+e- -> WW -> (q_1 qbar_2)(q_3 qbar_4) the usual hadronization models treat the colour singlets q_1 qbar_2 and q_3 qbar_4 coming from two W bosons independently. However, since the final state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as Colour Reconnection. In this article the results of the investigation of Colour Reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its kappa parameter most compatible with the data was found to be: kappa_{SK-I} = 2.2^{+2.5}_{-1.3} corresponding to the probability of reconnection P_{reco} to be in the range 0.31 < P_{reco} < 0.68 at 68% confidence level with its best value at 0.52.

0704.0598

Ignazio Licata

Ignazio Licata, Luigi Lella

Evolutionary Neural Gas (ENG): A Model of Self Organizing Network from Input Categorization

16 pages, 8 figures

EJTP,vol.4,, No.14 (2007),31-50

physics.gen-ph q-bio.PE

Despite their claimed biological plausibility, most self organizing networks have strict topological constraints and consequently they cannot take into account a wide range of external stimuli. Furthermore their evolution is conditioned by deterministic laws which often are not correlated with the structural parameters and the global status of the network, as it should happen in a real biological system. In nature the environmental inputs are noise affected and fuzzy. Which thing sets the problem to investigate the possibility of emergent behaviour in a not strictly constrained net and subjected to different inputs. It is here presented a new model of Evolutionary Neural Gas (ENG) with any topological constraints, trained by probabilistic laws depending on the local distortion errors and the network dimension. The network is considered as a population of nodes that coexist in an ecosystem sharing local and global resources. Those particular features allow the network to quickly adapt to the environment, according to its dimensions. The ENG model analysis shows that the net evolves as a scale-free graph, and justifies in a deeply physical sense- the term gas here used.

0704.0599

Michael R. Norman

S. Di Matteo and M. R. Norman

X-ray Dichroism and the Pseudogap Phase of Cuprates

final version to be published in Phys Rev B: some calculational details added, clarification of XNLD contamination and biaxiality, more discussion on possible space groups and previous optics results

Phys Rev B 76, 014510 (2007)

10.1103/PhysRevB.76.014510

cond-mat.supr-con cond-mat.str-el

A recent polarized x-ray absorption experiment on the high temperature cuprate superconductor Bi2Sr2CaCu2O8 indicates the presence of broken parity symmetry below the temperature, T*, where a pseudogap appears in photoemission. We critically analyze the x-ray data, and conclude that a parity-breaking signal of the kind suggested is unlikely based on the crystal structures reported in the literature. Possible other origins of the observed dichroism signal are discussed. We propose x-ray scattering experiments that can be done in order to determine whether such alternative interpretations are valid or not.

0704.0600

Alexander Fish

Alexander Fish

Solvability of linear equations within weak mixing sets

30 pages, to appear in Israel Journal of Mathematics

math.CO math.DS

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

We introduce a new class of "random" subsets of natural numbers, WM sets. This class contains normal sets (sets whose characteristic function is a normal binary sequence). We establish necessary and sufficient conditions for solvability of systems of linear equations within every WM set and within every normal set. We also show that partition-regular system of linear equations with integer coefficients is solvable in any WM set.