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The birth of string theory | In this contribution we go through the developments that in the years 1968 to
1974 led from the Veneziano model to the bosonic string.
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Duality and Tameness | We prove a duality theorem for certain graded algebras and show by various
examples different kinds of failure of tameness of local cohomology.
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Generalized regularly discontinuous solutions of the Einstein equations | The physical consistency of the match of piecewise-$C^0$ metrics is
discussed. The mathematical theory of gravitational discontinuity hypersurfaces
is generalized to cover the match of regularly discontinuous metrics. The
mean-value differential geometry framework on a hypersurface is introduced, and
corresponding compatibility conditions are deduced. Examples of generalized
boundary layers, gravitational shock waves and thin shells are studied.
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A geometric realization of sl(6,C) | Given an orientable weakly self-dual manifold X of rank two, we build a
geometric realization of the Lie algebra sl(6,C) as a naturally defined algebra
L of endomorphisms of the space of differential forms of X. We provide an
explicit description of Serre generators in terms of natural generators of L.
This construction gives a bundle on X which is related to the search for a
natural Gauge theory on X. We consider this paper as a first step in the study
of a rich and interesting algebraic structure.
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Rigid subsets of symplectic manifolds | We show that there is an hierarchy of intersection rigidity properties of
sets in a closed symplectic manifold: some sets cannot be displaced by
symplectomorphisms from more sets than the others. We also find new examples of
rigidity of intersections involving, in particular, specific fibers of moment
maps of Hamiltonian torus actions, monotone Lagrangian submanifolds (following
the works of P.Albers and P.Biran-O.Cornea), as well as certain, possibly
singular, sets defined in terms of Poisson-commutative subalgebras of smooth
functions. In addition, we get some geometric obstructions to semi-simplicity
of the quantum homology of symplectic manifolds. The proofs are based on the
Floer-theoretical machinery of partial symplectic quasi-states.
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Multiple Parton Scattering in Nuclei: Quark-quark Scattering | Modifications to quark and antiquark fragmentation functions due to
quark-quark (antiquark) double scattering in nuclear medium are studied
systematically up to order \cal{O}(\alpha_{s}^2)$ in deeply inelastic
scattering (DIS) off nuclear targets. At the order $\cal{O}(\alpha_s^2)$,
twist-four contributions from quark-quark (antiquark) rescattering also exhibit
the Landau-Pomeranchuck-Midgal (LPM) interference feature similar to gluon
bremsstrahlung induced by multiple parton scattering. Compared to quark-gluon
scattering, the modification, which is dominated by $t$-channel quark-quark
(antiquark) scattering, is only smaller by a factor of $C_F/C_A=4/9$ times the
ratio of quark and gluon distributions in the medium. Such a modification is
not negligible for realistic kinematics and finite medium size. The
modifications to quark (antiquark) fragmentation functions from quark-antiquark
annihilation processes are shown to be determined by the antiquark (quark)
distribution density in the medium. The asymmetry in quark and antiquark
distributions in nuclei will lead to different modifications of quark and
antiquark fragmentation functions inside a nucleus, which qualitatively
explains the experimentally observed flavor dependence of the leading hadron
suppression in semi-inclusive DIS off nuclear targets. The quark-antiquark
annihilation processes also mix quark and gluon fragmentation functions in the
large fractional momentum region, leading to a flavor dependence of jet
quenching in heavy-ion collisions.
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Experimental modeling of physical laws | A physical law is represented by the probability distribution of a measured
variable. The probability density is described by measured data using an
estimator whose kernel is the instrument scattering function. The experimental
information and data redundancy are defined in terms of information entropy.
The model cost function, comprised of data redundancy and estimation error, is
minimized by the creation-annihilation process.
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Reducing SAT to 2-SAT | Description of a polynomial time reduction of SAT to 2-SAT of polynomial
size.
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Half-metallic silicon nanowires | From first-principles calculations, we predict that transition metal (TM)
atom doped silicon nanowires have a half-metallic ground state. They are
insulators for one spin-direction, but show metallic properties for the
opposite spin direction. At high coverage of TM atoms, ferromagnetic silicon
nanowires become metallic for both spin-directions with high magnetic moment
and may have also significant spin-polarization at the Fermi level. The
spin-dependent electronic properties can be engineered by changing the type of
dopant TM atoms, as well as the diameter of the nanowire. Present results are
not only of scientific interest, but can also initiate new research on
spintronic applications of silicon nanowires.
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On Equivariant Embedding of Hilbert C^* modules | We prove that an arbitrary (not necessarily countably generated) Hilbert
$G$-$\cla$ module on a G-C^* algebra $\cla$ admits an equivariant embedding
into a trivial $G-\cla$ module, provided G is a compact Lie group and its
action on $\cla$ is ergodic.
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Invariance and the twisted Chern character : a case study | We give details of the proof of the remark made in \cite{G2} that the Chern
characters of the canonical generators on the K homology of the quantum group
$SU_q(2)$ are not invariant under the natural $SU_q(2)$ coaction. Furthermore,
the conjecture made in \cite{G2} about the nontriviality of the twisted Chern
character coming from an odd equivariant spectral triple on $SU_q(2)$ is
settled in the affirmative.
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Placeholder Substructures III: A Bit-String-Driven ''Recipe Theory'' for
Infinite-Dimensional Zero-Divisor Spaces | Zero-divisors (ZDs) derived by Cayley-Dickson Process (CDP) from
N-dimensional hypercomplex numbers (N a power of 2, at least 4) can represent
singularities and, as N approaches infinite, fractals -- and thereby,scale-free
networks. Any integer greater than 8 and not a power of 2 generates a
meta-fractal or "Sky" when it is interpreted as the "strut constant" (S) of an
ensemble of octahedral vertex figures called "Box-Kites" (the fundamental
building blocks of ZDs). Remarkably simple bit-manipulation rules or "recipes"
provide tools for transforming one fractal genus into others within the context
of Wolfram's Class 4 complexity.
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Langmuir blodgett assembly of densely aligned single walled carbon
nanotubes from bulk materials | Single walled carbon nanotubes exhibit advanced electrical and surface
properties useful for high performance nanoelectronics. Important to future
manufacturing of nanotube circuits is large scale assembly of SWNTs into
aligned forms. Despite progress in assembly and oriented synthesis, pristine
SWNTs in aligned and close-packed form remain elusive and needed for high
current, speed and density devices through collective operations of parallel
SWNTs. Here, we develop a Langmuir Blodgett method achieving monolayers of
aligned SWNTs with dense packing, central to which is a non covalent polymer
functionalization by PmPV imparting high solubility and stability of SWNTs in
an organic solvent DCE. Pressure cycling or annealing during LB film
compression reduces hysteresis and facilitates high degree alignment and
packing of SWNTs characterized by microscopy and polarized Raman spectroscopy.
The monolayer SWNTs are readily patterned for device integration by
microfabrication, enabling the highest currents 3mA through the narrowest
regions packed with aligned SWNTs thus far.
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Quantum Phase Transition in the Four-Spin Exchange Antiferromagnet | We study the S=1/2 Heisenberg antiferromagnet on a square lattice with
nearest-neighbor and plaquette four-spin exchanges (introduced by A.W. Sandvik,
Phys. Rev. Lett. {\bf 98}, 227202 (2007).)
This model undergoes a quantum phase transition from a spontaneously
dimerized phase to N\'eel order at a critical coupling. We show that as the
critical point is approached from the dimerized side, the system exhibits
strong fluctuations in the dimer background, reflected in the presence of a
low-energy singlet mode, with a simultaneous rise in the triplet quasiparticle
density. We find that both singlet and triplet modes of high density condense
at the transition, signaling restoration of lattice symmetry. In our approach,
which goes beyond mean-field theory in terms of the triplet excitations, the
transition appears sharp; however since our method breaks down near the
critical point, we argue that we cannot make a definite conclusion regarding
the order of the transition.
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Smooth maps with singularities of bounded K-codimensions | We will prove the relative homotopy principle for smooth maps with
singularities of a given {\cal K}-invariant class with a mild condition. We
next study a filtration of the group of homotopy self-equivalences of a given
manifold P by considering singularities of non-negative {\cal K}-codimensions.
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Stringy Jacobi fields in Morse theory | We consider the variation of the surface spanned by closed strings in a
spacetime manifold. Using the Nambu-Goto string action, we induce the geodesic
surface equation, the geodesic surface deviation equation which yields a Jacobi
field, and we define the index form of a geodesic surface as in the case of
point particles to discuss conjugate strings on the geodesic surface.
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Lower ground state due to counter-rotating wave interaction in trapped
ion system | We consider a single ion confined in a trap under radiation of two traveling
waves of lasers. In the strong-excitation regime and without the restriction of
Lamb-Dicke limit, the Hamiltonian of the system is similar to a driving
Jaynes-Cummings model without rotating wave approximation (RWA). The approach
we developed enables us to present a complete eigensolutions, which makes it
available to compare with the solutions under the RWA. We find that, the ground
state in our non-RWA solution is energically lower than the counterpart under
the RWA. If we have the ion in the ground state, it is equivalent to a spin
dependent force on the trapped ion. Discussion is made for the difference
between the solutions with and without the RWA, and for the relevant
experimental test, as well as for the possible application in quantum
information processing.
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Strained single-crystal Al2O3 grown layer-by-layer on Nb (110) thin
films | We report on the layer-by-layer growth of single-crystal Al2O3 thin-films on
Nb (110). Single-crystal Nb films are first prepared on A-plane sapphire,
followed by the evaporation of Al in an O2 background. The first stages of
Al2O3 growth are layer-by-layer with hexagonal symmetry. Electron and x-ray
diffraction measurements indicate the Al2O3 initially grows clamped to the Nb
lattice with a tensile strain near 10%. This strain relaxes with further
deposition, and beyond about 5 nm we observe the onset of island growth.
Despite the asymmetric misfit between the Al2O3 film and the Nb under-layer,
the observed strain is surprisingly isotropic.
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Quasi-quartet crystal electric field ground state in a tetragonal
CeAg$_2$Ge$_2$ single crystal | We have successfully grown the single crystals of CeAg$_2$Ge$_2$, for the
first time, by flux method and studied the anisotropic physical properties by
measuring the electrical resistivity, magnetic susceptibility and specific
heat. We found that CeAg$_2$Ge$_2$ undergoes an antiferromagnetic transition at
$T_{\rm N}$ = 4.6 K. The electrical resistivity and susceptibility data reveal
strong anisotropic magnetic properties. The magnetization measured at $T$ = 2 K
exhibited two metamagnetic transitions at $H_{\rm m1}$ = 31 kOe and $H_{\rm
m2}$ = 44.7 kOe, for $H \parallel$ [100] with a saturation magnetization of 1.6
$\mu_{\rm B}$/Ce. The crystalline electric field (CEF) analysis of the inverse
susceptibility data reveals that the ground state and the first excited states
of CeAg$_2$Ge$_2$ are closely spaced indicating a quasi-quartet ground state.
The specific heat data lend further support to the presence of closely spaced
energy levels.
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Strong Phase and $D^0-D^0bar$ mixing at BES-III | Most recently, both BaBar and Belle experiments found evidences of neutral
$D$ mixing. In this paper, we discuss the constraints on the strong phase
difference in $D^0 \to K\pi$ decay from the measurements of the mixing
parameters, $y^\prime$, $y_{CP}$ and $x$ at the $B$ factories. The sensitivity
of the measurement of the mixing parameter $y$ is estimated in BES-III
experiment at $\psi(3770)$ peak. We also make an estimate on the measurements
of the mixing rate $R_M$. Finally, the sensitivity of the strong phase
difference at BES-III are obtained by using data near the $D\bar{D}$ threshold
with CP tag technique at BES-III experiment.
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Meta-Stable Brane Configuration of Product Gauge Groups | Starting from the N=1 SU(N_c) x SU(N_c') gauge theory with fundamental and
bifundamental flavors, we apply the Seiberg dual to the first gauge group and
obtain the N=1 dual gauge theory with dual matters including the gauge
singlets. By analyzing the F-term equations of the superpotential, we describe
the intersecting type IIA brane configuration for the meta-stable
nonsupersymmetric vacua of this gauge theory. By introducing an orientifold
6-plane, we generalize to the case for N=1 SU(N_c) x SO(N_c') gauge theory with
fundamental and bifundamental flavors. Finally, the N=1 SU(N_c) x Sp(N_c')
gauge theory with matters is also described very briefly.
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Spinor dipolar Bose-Einstein condensates; Classical spin approach | Magnetic dipole-dipole interaction dominated Bose-Einstein condensates are
discussed under spinful situations. We treat the spin degrees of freedom as a
classical spin vector, approaching from large spin limit to obtain an effective
minimal Hamiltonian; a version extended from a non-linear sigma model. By
solving the Gross-Pitaevskii equation we find several novel spin textures where
the mass density and spin density are strongly coupled, depending upon trap
geometries due to the long-range and anisotropic natures of the dipole-dipole
interaction.
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Nonlinear Dynamics of the Phonon Stimulated Emission in Microwave
Solid-State Resonator of the Nonautonomous Phaser Generator | The microwave phonon stimulated emission (SE) has been experimentally and
numerically investigated in a nonautonomous microwave acoustic quantum
generator, called also microwave phonon laser or phaser (see previous works
arXiv:cond-mat/0303188 ; arXiv:cond-mat/0402640 ; arXiv:nlin.CG/0703050)
Phenomena of branching and long-time refractority (absence of the reaction on
the external pulses) for deterministic chaotic and regular processes of SE were
observed in experiments with various levels of electromagnetic pumping. At the
pumping level growth, the clearly depined increasing of the number of
coexisting SE states has been observed both in real physical experiments and in
computer simulations. This confirms the analytical estimations of the branching
density in the phase space. The nature of the refractority of SE pulses is
closely connected with the pointed branching and reflects the crises of strange
attractors, i.e. their collisions with unstable periodic components of the
higher branches of SE states in the nonautonomous microwave phonon laser.
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Proper J-holomorphic discs in Stein domains of dimension 2 | We prove the existence of global Bishop discs in a strictly pseudoconvex
Stein domain in an almost complex manifold of complex dimension 2.
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Anisotropic thermo-elasticity in 2D -- Part I: A unified approach | In this note we develop tools and techniques for the treatment of anisotropic
thermo-elasticity in two space dimensions. We use a diagonalisation technique
to obtain properties of the characteristic roots of the full symbol of the
system in order to prove $L^p$--$L^q$ decay rates for its solutions.
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I-V characteristics of the vortex state in MgB2 thin films | The current-voltage (I-V) characteristics of various MgB2 films have been
studied at different magnetic fields parallel to c-axis. At fields \mu0H
between 0 and 5T, vortex liquid-glass transitions were found in the I-V
isotherms. Consistently, the I-V curves measured at different temperatures show
a scaling behavior in the framework of quasi-two-dimension (quasi-2D) vortex
glass theory. However, at \mu0 H >= 5T, a finite dissipation was observed down
to the lowest temperature here, T=1.7K, and the I-V isotherms did not scale in
terms of any known scaling law, of any dimensionality. We suggest that this may
be caused by a mixture of \sigma band vortices and \pi band quasiparticles.
Interestingly, the I-V curves at zero magnetic field can still be scaled
according to the quasi-2D vortex glass formalism, indicating an equivalent
effect of self-field due to persistent current and applied magnetic field.
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Magnetic Fingerprints of sub-100 nm Fe Nanodots | Sub-100 nm nanomagnets not only are technologically important, but also
exhibit complex magnetization reversal behaviors as their dimensions are
comparable to typical magnetic domain wall widths. Here we capture magnetic
"fingerprints" of 1 billion Fe nanodots as they undergo a single domain to
vortex state transition, using a first-order reversal curve (FORC) method. As
the nanodot size increases from 52 nm to 67 nm, the FORC diagrams reveal
striking differences, despite only subtle changes in their major hysteresis
loops. The 52 nm nanodots exhibit single domain behavior and the coercivity
distribution extracted from the FORC distribution agrees well with a
calculation based on the measured nanodot size distribution. The 58 and 67 nm
nanodots exhibit vortex states, where the nucleation and annihilation of the
vortices are manifested as butterfly-like features in the FORC distribution and
confirmed by micromagnetic simulations. Furthermore, the FORC method gives
quantitative measures of the magnetic phase fractions, and vortex nucleation
and annihilation fields.
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An online repository of Swift/XRT light curves of GRBs | Context. Swift data are revolutionising our understanding of Gamma Ray
Bursts. Since bursts fade rapidly, it is desirable to create and disseminate
accurate light curves rapidly.
Aims. To provide the community with an online repository of X-ray light
curves obtained with Swift. The light curves should be of the quality expected
of published data, but automatically created and updated so as to be
self-consistent and rapidly available. Methods. We have produced a suite of
programs which automatically generates Swift/XRT light curves of GRBs. Effects
of the damage to the CCD, automatic readout-mode switching and pile-up are
appropriately handled, and the data are binned with variable bin durations, as
necessary for a fading source.
Results. The light curve repository website
(http://www.swift.ac.uk/xrt_curves) contains light curves, hardness ratios and
deep images for every GRB which Swift's XRT has observed. When new GRBs are
detected, light curves are created and updated within minutes of the data
arriving at the UK Swift Science Data Centre.
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On the total disconnectedness of the quotient Aubry set | In this paper we show that the quotient Aubry set associated to certain
Lagrangians is totally disconnected (i.e., every connected component consists
of a single point). Moreover, we discuss the relation between this problem and
a Morse-Sard type property for (difference of) critical subsolutions of
Hamilton-Jacobi equations.
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New simple modular Lie superalgebras as generalized prolongs | Over algebraically closed fields of characteristic p>2, prolongations of the
simple finite dimensional Lie algebras and Lie superalgebras with Cartan matrix
are studied for certain simplest gradings of these algebras. Several new simple
Lie superalgebras are discovered, serial and exceptional, including superBrown
and superMelikyan superalgebras. Simple Lie superalgebras with Cartan matrix of
rank 2 are classified.
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Vacuum Structure and Potential | Based on overall experimental observations, especially the pair processes, I
developed a model structure of the vacuum along with a basic-particle formation
scheme begun in 2000 (with collaborator P-I Johansson). The model consists in
that the vacuum is, briefly, filled of neutral but polarizable vacuuons,
consisting each of a p-vaculeon and n- vaculeon of charges $+e$ and $-e$ of
zero rest masses but with spin motions, assumed interacting each other with a
Coulomb force. The model has been introduced in full in a book (Nova Sci, 2005)
and referred to in a number of journal/E-print papers. I outline in this easier
accessible paper the detailed derivation of the model and a corresponding
quantitative determination of the vacuuon size.
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Counterflow of electrons in two isolated quantum point contacts | We study the interaction between two adjacent but electrically isolated
quantum point contacts (QPCs). At high enough source-drain bias on one QPC, the
drive QPC, we detect a finite electric current in the second, unbiased,
detector QPC. The current generated at the detector QPC always flows in the
opposite direction than the current of the drive QPC. The generated current is
maximal, if the detector QPC is tuned to a transition region between its
quantized conductance plateaus and the drive QPC is almost pinched-off. We
interpret this counterflow phenomenon in terms of an asymmetric phonon-induced
excitation of electrons in the leads of the detector QPC.
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PAH emission and star formation in the host of the z~2.56 Cloverleaf QSO | We report the first detection of the 6.2micron and 7.7micron infrared `PAH'
emission features in the spectrum of a high redshift QSO, from the Spitzer-IRS
spectrum of the Cloverleaf lensed QSO (H1413+117, z~2.56). The ratio of PAH
features and rest frame far-infrared emission is the same as in lower
luminosity star forming ultraluminous infrared galaxies and in local PG QSOs,
supporting a predominantly starburst nature of the Cloverleaf's huge
far-infrared luminosity (5.4E12 Lsun, corrected for lensing). The Cloverleaf's
period of dominant QSO activity (Lbol ~ 7E13 Lsun) is coincident with an
intense (star formation rate ~1000 Msun/yr) and short (gas exhaustion time
~3E7yr) star forming event.
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Causal dissipative hydrodynamics for QGP fluid in 2+1 dimensions | In 2nd order causal dissipative theory, space-time evolution of QGP fluid is
studied in 2+1 dimensions. Relaxation equations for shear stress tensors are
solved simultaneously with the energy-momentum conservation equations.
Comparison of evolution of ideal and viscous QGP fluid, initialized under the
same conditions, e.g. same equilibration time, energy density and velocity
profile, indicate that in a viscous dynamics, energy density or temperature of
the fluid evolve slowly, than in an ideal fluid. Cooling gets slower as
viscosity increases. Transverse expansion also increases in a viscous dynamics.
For the first time we have also studied elliptic flow of 'quarks' in causal
viscous dynamics. It is shown that elliptic flow of quarks saturates due to
non-equilibrium correction to equilibrium distribution function, and can not be
mimicked by an ideal hydrodynamics.
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A Single Trapped Ion as a Time-Dependent Harmonic Oscillator | We show how a single trapped ion may be used to test a variety of important
physical models realized as time-dependent harmonic oscillators. The ion itself
functions as its own motional detector through laser-induced electronic
transitions. Alsing et al. [Phys. Rev. Lett. 94, 220401 (2005)] proposed that
an exponentially decaying trap frequency could be used to simulate (thermal)
Gibbons-Hawking radiation in an expanding universe, but the Hamiltonian used
was incorrect. We apply our general solution to this experimental proposal,
correcting the result for a single ion and showing that while the actual
spectrum is different from the Gibbons-Hawking case, it nevertheless shares an
important experimental signature with this result.
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Compounding Fields and Their Quantum Equations in the Trigintaduonion
Space | The 32-dimensional compounding fields and their quantum interplays in the
trigintaduonion space can be presented by analogy with octonion and sedenion
electromagnetic, gravitational, strong and weak interactions. In the
trigintaduonion fields which are associated with the electromagnetic,
gravitational, strong and weak interactions, the study deduces some conclusions
of field source particles (quarks and leptons) and intermediate particles which
are consistent with current some sorts of interaction theories. In the
trigintaduonion fields which are associated with the hyper-strong and
strong-weak fields, the paper draws some predicts and conclusions of the field
source particles (sub-quarks) and intermediate particles. The research results
show that there may exist some new particles in the nature.
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Topological defects, geometric phases, and the angular momentum of light | Recent reports on the intriguing features of vector vortex bearing beams are
analyzed using geometric phases in optics. It is argued that the spin
redirection phase induced circular birefringence is the origin of topological
phase singularities arising in the inhomogeneous polarization patterns. A
unified picture of recent results is presented based on this proposition.
Angular momentum shift within the light beam (OAM) has exact equivalence with
the angular momentum holonomy associated with the geometric phase consistent
with our conjecture.
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Circular and non-circular nearly horizon-skimming orbits in Kerr
spacetimes | We have performed a detailed analysis of orbital motion in the vicinity of a
nearly extremal Kerr black hole. For very rapidly rotating black holes (spin
a=J/M>0.9524M) we have found a class of very strong field eccentric orbits
whose angular momentum L_z increases with the orbit's inclination with respect
to the equatorial plane, while keeping latus rectum and eccentricity fixed.
This behavior is in contrast with Newtonian intuition, and is in fact opposite
to the "normal" behavior of black hole orbits. Such behavior was noted
previously for circular orbits; since it only applies to orbits very close to
the black hole, they were named "nearly horizon-skimming orbits". Our analysis
generalizes this result, mapping out the full generic (inclined and eccentric)
family of nearly horizon-skimming orbits. The earlier work on circular orbits
reported that, under gravitational radiation emission, nearly horizon-skimming
orbits tend to evolve to smaller orbit inclination, toward prograde equatorial
configuration. Normal orbits, by contrast, always demonstrate slowly growing
orbit inclination (orbits evolve toward the retrograde equatorial
configuration). Using up-to-date Teukolsky-fluxes, we have concluded that the
earlier result was incorrect: all circular orbits, including nearly
horizon-skimming ones, exhibit growing orbit inclination. Using kludge fluxes
based on a Post-Newtonian expansion corrected with fits to circular and to
equatorial Teukolsky-fluxes, we argue that the inclination grows also for
eccentric nearly horizon-skimming orbits. We also find that the inclination
change is, in any case, very small. As such, we conclude that these orbits are
not likely to have a clear and peculiar imprint on the gravitational waveforms
expected to be measured by the space-based detector LISA.
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The Blue Straggler Population of the Globular Cluster M5 | By combining high-resolution HST and wide-field ground based observations, in
ultraviolet and optical bands, we study the Blue Stragglers Star (BSS)
population of the galactic globular cluster M5 (NGC 5904) from its very central
regions up to its periphery. The BSS distribution is highly peaked in the
cluster center, decreases at intermediate radii and rises again outward. Such a
bimodal distribution is similar to those previously observed in other globular
clusters (M3, 47Tucanae, NGC6752). As for these clusters, dynamical simulations
suggest that, while the majority of BSS in M5 could be originated by stellar
collisions, a significant fraction (20-40%) of BSS generated by mass transfer
processes in primordial binaries is required to reproduce the observed radial
distribution. A candidate BSS has been detected beyond the cluster tidal
radius. If confirmed, this could represent an interesting case of an
"evaporating" BSS.
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Entanglement entropy of two-dimensional Anti-de Sitter black holes | Using the AdS/CFT correspondence we derive a formula for the entanglement
entropy of the anti-de Sitter black hole in two spacetime dimensions. The
leading term in the large black hole mass expansion of our formula reproduces
exactly the Bekenstein-Hawking entropy S_{BH}, whereas the subleading term
behaves as ln S_{BH}. This subleading term has the universal form typical for
the entanglement entropy of physical systems described by effective conformal
fields theories (e.g. one-dimensional statistical models at the critical
point). The well-known form of the entanglement entropy for a two-dimensional
conformal field theory is obtained as analytic continuation of our result and
is related with the entanglement entropy of a black hole with negative mass.
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Towards self-consistent definition of instanton liquid parameters | The possibility of self-consistent determination of instanton liquid
parameters is discussed together with the definition of optimal pseudo-particle
configurations and comparing the various pseudo-particle ensembles. The
weakening of repulsive interactions between pseudo-particles is argued and
estimated.
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Some aspects of the nonperturbative renormalization of the phi^4 model | A nonperturbative renormalization of the phi^4 model is considered. First we
integrate out only a single pair of conjugated modes with wave vectors +/- q.
Then we are looking for the RG equation which would describe the transformation
of the Hamiltonian under the integration over a shell Lambda - d Lambda < k <
Lambda, where d Lambda -> 0. We show that the known Wegner--Houghton equation
is consistent with the assumption of a simple superposition of the integration
results for +/- q. The renormalized action can be expanded in powers of the
phi^4 coupling constant u in the high temperature phase at u -> 0. We compare
the expansion coefficients with those exactly calculated by the diagrammatic
perturbative method, and find some inconsistency. It causes a question in which
sense the Wegner-Houghton equation is really exact.
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Instanton Liquid at Finite Temperature and Chemical Potential of Quarks | Instanton liquid in heated and strongly interacting matter is studied using
the variational principle. The dependence of the instanton liquid density
(gluon condensate) on the temperature and the quark chemical potential is
determined under the assumption that, at finite temperatures, the dominant
contribution is given by an ensemble of calorons. The respective one-loop
effective quark Lagrangian is used.
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Eternal inflation and localization on the landscape | We model the essential features of eternal inflation on the landscape of a
dense discretuum of vacua by the potential $V(\phi)=V_{0}+\delta V(\phi)$,
where $|\delta V(\phi)|\ll V_{0}$ is random. We find that the diffusion of the
distribution function $\rho(\phi,t)$ of the inflaton expectation value in
different Hubble patches may be suppressed due to the effect analogous to the
Anderson localization in disordered quantum systems. At $t \to \infty$ only the
localized part of the distribution function $\rho (\phi, t)$ survives which
leads to dynamical selection principle on the landscape. The probability to
measure any but a small value of the cosmological constant in a given Hubble
patch on the landscape is exponentially suppressed at $t\to \infty$.
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Singularity Resolution in Isotropic Loop Quantum Cosmology: Recent
Developments | Since the past Iagrg meeting in December 2004, new developments in loop
quantum cosmology have taken place, especially with regards to the resolution
of the Big Bang singularity in the isotropic models. The singularity resolution
issue has been discussed in terms of physical quantities (expectation values of
Dirac observables) and there is also an ``improved'' quantization of the
Hamiltonian constraint. These developments are briefly discussed.
This is an expanded version of the review talk given at the
24$^{\mathrm{th}}$ IAGRG meeting in February 2007.
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Vortices in Bose-Einstein Condensates: Theory | Vortices are pervasive in nature, representing the breakdown of laminar fluid
flow and hence playing a key role in turbulence. The fluid rotation associated
with a vortex can be parameterized by the circulation $\Gamma=\oint {\rm d}{\bf
r}\cdot{\bf v}({\bf r})$ about the vortex, where ${\bf v}({\bf r})$ is the
fluid velocity field. While classical vortices can take any value of
circulation, superfluids are irrotational, and any rotation or angular momentum
is constrained to occur through vortices with quantized circulation. Quantized
vortices also play a key role in the dissipation of transport in superfluids.
In BECs quantized vortices have been observed in several forms, including
single vortices, vortex lattices, and vortex pairs and rings. The recent
observation of quantized vortices in a fermionic gas was taken as a clear
signature of the underlying condensation and superfluidity of fermion pairs. In
addition to BECs, quantized vortices also occur in superfluid Helium, nonlinear
optics, and type-II superconductors.
|
A POVM view of the ensemble approach to polarization optics | Statistical ensemble formalism of Kim, Mandel and Wolf (J. Opt. Soc. Am. A 4,
433 (1987)) offers a realistic model for characterizing the effect of
stochastic non-image forming optical media on the state of polarization of
transmittedlight. With suitable choice of the Jones ensemble, various Mueller
transformations - some of which have been unknown so far - are deduced. It is
observed that the ensemble approach is formally identical to the positive
operator valued measures (POVM) on the quantum density matrix. This
observation, in combination with the recent suggestion by Ahnert and Payne
(Phys. Rev. A 71, 012330, (2005)) - in the context of generalized quantum
measurement on single photon polarization states - that linear optics elements
can be employed in setting up all possible POVMs, enables us to propose a way
of realizing different types of Mueller devices.
|
Reexamination of spin decoherence in semiconductor quantum dots from
equation-of-motion approach | The longitudinal and transversal spin decoherence times, $T_1$ and $T_2$, in
semiconductor quantum dots are investigated from equation-of-motion approach
for different magnetic fields, quantum dot sizes, and temperatures. Various
mechanisms, such as the hyperfine interaction with the surrounding nuclei, the
Dresselhaus spin-orbit coupling together with the electron--bulk-phonon
interaction, the $g$-factor fluctuations, the direct spin-phonon coupling due
to the phonon-induced strain, and the coaction of the
electron--bulk/surface-phonon interaction together with the hyperfine
interaction are included. The relative contributions from these spin
decoherence mechanisms are compared in detail. In our calculation, the
spin-orbit coupling is included in each mechanism and is shown to have marked
effect in most cases. The equation-of-motion approach is applied in studying
both the spin relaxation time $T_1$ and the spin dephasing time $T_2$, either
in Markovian or in non-Markovian limit. When many levels are involved at finite
temperature, we demonstrate how to obtain the spin relaxation time from the
Fermi Golden rule in the limit of weak spin-orbit coupling. However, at high
temperature and/or for large spin-orbit coupling, one has to use the
equation-of-motion approach when many levels are involved. Moreover, spin
dephasing can be much more efficient than spin relaxation at high temperature,
though the two only differs by a factor of two at low temperature.
|
Construction of initial data for 3+1 numerical relativity | This lecture is devoted to the problem of computing initial data for the
Cauchy problem of 3+1 general relativity. The main task is to solve the
constraint equations. The conformal technique, introduced by Lichnerowicz and
enhanced by York, is presented. Two standard methods, the conformal
transverse-traceless one and the conformal thin sandwich, are discussed and
illustrated by some simple examples. Finally a short review regarding initial
data for binary systems (black holes and neutron stars) is given.
|
Magnetism and Thermodynamics of Spin-1/2 Heisenberg Diamond Chains in a
Magnetic Field | The magnetic and thermodynamic properties of spin-1/2 Heisenberg diamond
chains are investigated in three different cases: (a) J1, J2, J3>0
(frustrated); (b) J1, J3<0, J2>0 (frustrated); and (c) J1, J2>0, J3<0
(non-frustrated). The density matrix renormalization group (DMRG) technique is
invoked to study the properties of the system in the ground state, while the
transfer matrix renormalization group (TMRG) technique is applied to explore
the thermodynamic properties. The local magnetic moments, spin correlation
functions, and static structure factors are discussed in the ground state for
the three cases. It is shown that the static structure factor S(q) shows peaks
at wavevectors $q=a\pi /3$ (a=0,1,2,3,4,5) for different couplings in a zero
magnetic field, which, however in the magnetic fields where the magnetization
plateau with m=1/6 pertains, exhibits the peaks only at q=0, $2\pi /3$ and
$4\pi /3$, which are found to be couplings-independent. The DMRG results of the
zero-field static structure factor can be nicely fitted by a linear
superposition of six modes, where two fitting equations are proposed. It is
observed that the six modes are closely related to the low-lying excitations of
the system. At finite temperatures, the double-peak structures of the
susceptibility and specific heat against temperature are obtained, where the
peak positions and heights are found to depend on the competition of the
couplings. It is also uncovered that the XXZ anisotropy of F and AF couplings
leads the system of case (c) to display quite different behaviors. In addition,
the experimental data of the susceptibility, specific heat and magnetization
for the compound Cu$_{3}$(CO$_{3}$)$_{2}$(OH)$_{2}$ are fairly compared with
our TMRG results.
|
Extraction of physical laws from joint experimental data | The extraction of a physical law y=yo(x) from joint experimental data about x
and y is treated. The joint, the marginal and the conditional probability
density functions (PDF) are expressed by given data over an estimator whose
kernel is the instrument scattering function. As an optimal estimator of yo(x)
the conditional average is proposed. The analysis of its properties is based
upon a new definition of prediction quality. The joint experimental information
and the redundancy of joint measurements are expressed by the relative entropy.
With the number of experiments the redundancy on average increases, while the
experimental information converges to a certain limit value. The difference
between this limit value and the experimental information at a finite number of
data represents the discrepancy between the experimentally determined and the
true properties of the phenomenon. The sum of the discrepancy measure and the
redundancy is utilized as a cost function. By its minimum a reasonable number
of data for the extraction of the law yo(x) is specified. The mutual
information is defined by the marginal and the conditional PDFs of the
variables. The ratio between mutual information and marginal information is
used to indicate which variable is the independent one. The properties of the
introduced statistics are demonstrated on deterministically and randomly
related variables.
|
Kinetic equation for finite systems of fermions with pairing | The solutions of the Wigner-transformed time-dependent
Hartree--Fock--Bogoliubov equations are studied in the constant-$\Delta$
approximation. This approximation is known to violate particle-number
conservation. As a consequence, the density fluctuation and the longitudinal
response function given by this approximation contain spurious contributions. A
simple prescription for restoring both local and global particle-number
conservation is proposed. Explicit expressions for the eigenfrequencies of the
correlated systems and for the density response function are derived and it is
shown that the semiclassical analogous of the quantum single--particle spectrum
has an excitation gap of $2\Delta$, in agreement with the quantum result. The
collective response is studied for a simplified form of the residual
interaction.
|
Reciprocal Symmetry and Classical Discrete Oscillator Incorporating
Half-Integral Energy Levels | Classical oscillator differential equation is replaced by the corresponding
(finite time) difference equation. The equation is, then, symmetrized so that
it remains invariant under the change d going to -d, where d is the smallest
span of time. This symmetric equation has solutions, which come in reciprocally
related pairs. One member of a pair agrees with the classical solution and the
other is an oscillating solution and does not converge to a limit as d goes to
0. This solution contributes to oscillator energy a term which is a multiple of
half-integers.
|
Hadrons in Medium -- Theory confronts experiment | In this talk we briefly summarize our theoretical understanding of in-medium
selfenergies of hadrons. With the special case of the $\omega$ meson we
demonstrate that earlier calculations that predicted a significant lowering of
the mass in medium are based on an incorrect treatment of the model Lagrangian;
more consistent calculations lead to a significant broadening, but hardly any
mass shift. We stress that the experimental reconstruction of hadron spectral
functions from measured decay products always requires knowledge of the decay
branching ratios which may also be strongly mass-dependent. It also requires a
quantitatively reliable treatment of final state interactions which has to be
part of any reliable theory.
|
A computer program for fast non-LTE analysis of interstellar line
spectra | The large quantity and high quality of modern radio and infrared line
observations require efficient modeling techniques to infer physical and
chemical parameters such as temperature, density, and molecular abundances. We
present a computer program to calculate the intensities of atomic and molecular
lines produced in a uniform medium, based on statistical equilibrium
calculations involving collisional and radiative processes and including
radiation from background sources. Optical depth effects are treated with an
escape probability method. The program is available on the World Wide Web at
http://www.sron.rug.nl/~vdtak/radex/index.shtml . The program makes use of
molecular data files maintained in the Leiden Atomic and Molecular Database
(LAMDA), which will continue to be improved and expanded. The performance of
the program is compared with more approximate and with more sophisticated
methods. An Appendix provides diagnostic plots to estimate physical parameters
from line intensity ratios of commonly observed molecules. This program should
form an important tool in analyzing observations from current and future radio
and infrared telescopes.
|
Nonlinear force-free coronal magnetic field extrapolation scheme based
on the direct boundary integral formulation | This paper has been withdrawn by the authors.
|
Alternative Approaches to the Equilibrium Properties of Hard-Sphere
Liquids | An overview of some analytical approaches to the computation of the
structural and thermodynamic properties of single component and multicomponent
hard-sphere fluids is provided. For the structural properties, they yield a
thermodynamically consistent formulation, thus improving and extending the
known analytical results of the Percus-Yevick theory. Approximate expressions
for the contact values of the radial distribution functions and the
corresponding analytical equations of state are also discussed. Extensions of
this methodology to related systems, such as sticky hard spheres and
square-well fluids, as well as its use in connection with the perturbation
theory of fluids are briefly addressed.
|
Complexities of Human Promoter Sequences | By means of the diffusion entropy approach, we detect the scale-invariance
characteristics embedded in the 4737 human promoter sequences. The exponent for
the scale-invariance is in a wide range of $[ {0.3,0.9} ]$, which centered at
$\delta_c = 0.66$. The distribution of the exponent can be separated into left
and right branches with respect to the maximum. The left and right branches are
asymmetric and can be fitted exactly with Gaussian form with different widths,
respectively.
|
Evidence for an excitonic insulator phase in 1T-TiSe$_{2}$ | We present a new high-resolution angle-resolved photoemission study of
1\textit{T}-TiSe$_{2}$ in both, its room-temperature, normal phase and its
low-temperature, charge-density wave phase. At low temperature the
photoemission spectra are strongly modified, with large band renormalisations
at high-symmetry points of the Brillouin zone and a very large transfer of
spectral weight to backfolded bands. A theoretical calculation of the spectral
function for an excitonic insulator phase reproduces the experimental features
with very good agreement. This gives strong evidence in favour of the excitonic
insulator scenario as a driving force for the charge-density wave transition in
1\textit{T}-TiSe$_{2}$.
|
Oxygen-rich droplets and the enrichment of the ISM | We argue that the discrepancies observed in HII regions between abundances
derived from optical recombination lines (ORLs) and collisionally excited lines
(CELs) might well be the signature of a scenario of the enrichment of the
interstellar medium (ISM) proposed by Tenorio-Tagle (1996). In this scenario,
the fresh oxygen released during massive supernova explosions is confined
within the hot superbubbles as long as supernovae continue to explode. Only
after the last massive supernova explosion, the metal-rich gas starts cooling
down and falls on the galaxy within metal-rich droplets. Full mixing of these
metal-rich droplets and the ISM occurs during photoionization by the next
generations of massive stars. During this process, the metal-rich droplets give
rise to strong recombination lines of the metals, leading to the observed
ORL-CEL discrepancy. (The full version of this work is submitted to Astronomy
and Astrophysics.)
|
Soft modes and NTE in Zn(CN)2 from Raman spectroscopy and first
principles calculations | We have studied Zn(CN)2 at high pressure using Raman spectroscopy, and report
Gruneisen parameters of the soft phonons. The phonon frequencies and eigen
vectors obtained from ab-initio calculations are used for the assignment of the
observed phonon spectra. Out of the eleven zone-centre optical modes, six modes
exhibit negative Gruneisen parameter. The calculations suggest that the soft
phonons correspond to the librational and translational modes of CN rigid unit,
with librational modes contributing more to thermal expansion. A rapid
disordering of the lattice is found above 1.6 GPa from X-ray diffraction.
|
Estimation of experimental data redundancy and related statistics | Redundancy of experimental data is the basic statistic from which the
complexity of a natural phenomenon and the proper number of experiments needed
for its exploration can be estimated. The redundancy is expressed by the
entropy of information pertaining to the probability density function of
experimental variables. Since the calculation of entropy is inconvenient due to
integration over a range of variables, an approximate expression for redundancy
is derived that includes only a sum over the set of experimental data about
these variables. The approximation makes feasible an efficient estimation of
the redundancy of data along with the related experimental information and
information cost function. From the experimental information the complexity of
the phenomenon can be simply estimated, while the proper number of experiments
needed for its exploration can be determined from the minimum of the cost
function. The performance of the approximate estimation of these statistics is
demonstrated on two-dimensional normally distributed random data.
|
Effective potentials for quasicrystals from ab-initio data | Classical effective potentials are indispensable for any large-scale
atomistic simulations, and the relevance of simulation results crucially
depends on the quality of the potentials used. For complex alloys like
quasicrystals, however, realistic effective potentials are practically
inexistent. We report here on our efforts to develop effective potentials
especially for quasicrystalline alloy systems. We use the so-called force
matching method, in which the potential parameters are adapted so as to
optimally reproduce the forces and energies in a set of suitably chosen
reference configurations. These reference data are calculated with ab-initio
methods. As a first application, EAM potentials for decagonal Al-Ni-Co,
icosahedral Ca-Cd, and both icosahedral and decagonal Mg-Zn quasicrystals have
been constructed. The influence of the potential range and degree of
specialisation on the accuracy and other properties is discussed and compared.
|
On smooth foliations with Morse singularities | Let $M$ be a smooth manifold and let $\F$ be a codimension one, $C^\infty$
foliation on $M$, with isolated singularities of Morse type. The study and
classification of pairs $(M,\F)$ is a challenging (and difficult) problem. In
this setting, a classical result due to Reeb \cite{Reeb} states that a manifold
admitting a foliation with exactly two center-type singularities is a sphere.
In particular this is true if the foliation is given by a function. Along these
lines a result due to Eells and Kuiper \cite{Ku-Ee} classify manifolds having a
real-valued function admitting exactly three non-degenerate singular points. In
the present paper, we prove a generalization of the above mentioned results. To
do this, we first describe the possible arrangements of pairs of singularities
and the corresponding codimension one invariant sets, and then we give an
elimination procedure for suitable center-saddle and some saddle-saddle
configurations (of consecutive indices). In the second part, we investigate if
other classical results, such as Haefliger and Novikov (Compact Leaf) theorems,
proved for regular foliations, still hold true in presence of singularities. At
this purpose, in the singular set, $Sing(\F)$ of the foliation $\F$, we
consider {\em{weakly stable}} components, that we define as those components
admitting a neighborhood where all leaves are compact. If $Sing(\F)$ admits
only weakly stable components, given by smoothly embedded curves diffeomorphic
to $S^1$, we are able to extend Haefliger's theorem. Finally, the existence of
a closed curve, transverse to the foliation, leads us to state a Novikov-type
result.
|
Frobenius-Schur indicators for semisimple Lie algebras | Let g be a finite dimensional complex semisimple Lie algebra, and let V be a
finite dimensional represenation of g. We give a closed formula for the mth
Frobenius-Schur indicator, m>1, of V in representation-theoretic terms. We
deduce that the indicators take integer values, and that for a large enough m,
the mth indicator of V equals the dimension of the zero weight space of V. For
the classical Lie algebras sl(n), so(2n), so(2n+1) and sp(2n), this is the case
for m greater or equal to 2n-1, 4n-5, 4n-3 and 2n+1, respectively.
|
Supersymmetry breaking metastable vacua in runaway quiver gauge theories | In this paper we consider quiver gauge theories with fractional branes whose
infrared dynamics removes the classical supersymmetric vacua (DSB branes). We
show that addition of flavors to these theories (via additional non-compact
branes) leads to local meta-stable supersymmetry breaking minima, closely
related to those of SQCD with massive flavors. We simplify the study of the
one-loop lifting of the accidental classical flat directions by direct
computation of the pseudomoduli masses via Feynman diagrams. This new approach
allows to obtain analytic results for all these theories. This work extends the
results for the $dP_1$ theory in hep-th/0607218. The new approach allows to
generalize the computation to general examples of DSB branes, and for arbitrary
values of the superpotential couplings.
|
Low Energy Aspects of Heavy Meson Decays | I discuss low energy aspects of heavy meson decays, where there is at least
one heavy meson in the final state. Examples are $B -\bar{B}$ mixing, $B \to D
\bar{D}$, $B \to D \eta'$, and $B \to D \gamma$. %and $B \to D W $ (Isgur-Wise
function). The analysis is performed in the heavy quark limit within
heavy-light chiral perturbation theory. Coefficients of $1/N_c$ suppressed
chiral Lagrangian terms (beyond factorization) have been estimated by means of
a heavy-light chiral quark model.
|
Radiative losses and cut-offs of energetic particles at relativistic
shocks | We investigate the acceleration and simultaneous radiative losses of
electrons in the vicinity of relativistic shocks. Particles undergo pitch angle
diffusion, gaining energy as they cross the shock by the Fermi mechanism and
also emitting synchrotron radiation in the ambient magnetic field. A
semi-analytic approach is developed which allows us to consider the behaviour
of the shape of the spectral cut-off and the variation of that cut-off with the
particle pitch angle. The implications for the synchrotron emission of
relativistic jets, such as those in gamma ray burst sources and blazars, are
discussed.
|
Very strong and slowly varying magnetic fields as source of axions | The investigation on the production of particles in slowly varying but
extremely intense magnetic field in extended to the case of axions. The
motivation is, as for some previously considered cases, the possibility that
such kind of magnetic field may exist around very compact astrophysical
objects.
|
Symmetry disquisition on the TiOX phase diagram | The sequence of phase transitions and the symmetry of in particular the low
temperature incommensurate and spin-Peierls phases of the quasi one-dimensional
inorganic spin-Peierls system TiOX (TiOBr and TiOCl) have been studied using
inelastic light scattering experiments. The anomalous first-order character of
the transition to the spin-Peierls phase is found to be a consequence of the
different symmetries of the incommensurate and spin-Peierls (P$2_{1}/m$)
phases.
The pressure dependence of the lowest transition temperature strongly
suggests that magnetic interchain interactions play an important role in the
formation of the spin-Peierls and the incommensurate phases. Finally, a
comparison of Raman data on VOCl to the TiOX spectra shows that the high energy
scattering observed previously has a phononic origin.
|
Discovery of a point-like very-high-energy gamma-ray source in Monoceros | The complex Monoceros Loop SNR/Rosette Nebula region contains several
potential sources of very-high-energy (VHE) gamma-ray emission and two as yet
unidentified high-energy EGRET sources. Sensitive VHE observations are required
to probe acceleration processes in this region. The H.E.S.S. telescope array
has been used to search for very high-energy gamma-ray sources in this region.
CO data from the NANTEN telescope were used to map the molecular clouds in the
region, which could act as target material for gamma-ray production via
hadronic interactions. We announce the discovery of a new gamma-ray source,
HESS J0632+058, located close to the rim of the Monoceros SNR. This source is
unresolved by H.E.S.S. and has no clear counterpart at other wavelengths but is
possibly associated with the weak X-ray source 1RXS J063258.3+054857, the
Be-star MWC 148 and/or the lower energy gamma-ray source 3EG J0634+0521. No
evidence for an associated molecular cloud was found in the CO data.
|
Thermal entanglement of qubit pairs on the Shastry-Sutherland lattice | We show that temperature and magnetic field properties of the entanglement
between spins on the two-dimensional Shastry-Sutherland lattice can be
qualitatively described by analytical results for a qubit tetramer. Exact
diagonalization of clusters with up to 20 sites reveals that the regime of
fully entangled neighboring pairs coincides with the regime of finite spin gap
in the spectrum. Additionally, the results for the regime of vanishing spin gap
are discussed and related to the Heisenberg limit of the model.
|
Bonding of H in O vacancies of ZnO | We investigate the bonding of H in O vacancies of ZnO using density
functional calculations. We find that H is anionic and does not form
multicenter bonds with Zn in this compound.
|
Reparametrization Invariance, the controversial extraction of $\alpha$
from $B\to\pi\pi$ and New Physics | The extraction of the weak phase $\alpha$ from $B\to\pi\pi$ decays has been
controversial from a statistical point of view, as the frequentist vs. bayesian
confrontation shows. We analyse several relevant questions which have not
deserved full attention and pervade the extraction of $\alpha$.
Reparametrization Invariance proves appropriate to understand those issues. We
show that some Standard Model inspired parametrizations can be senseless or
inadequate if they go beyond the minimal Gronau and London assumptions: the
single weak phase $\alpha$ just in the $\Delta I=3/2$ amplitudes, the isospin
relations and experimental data. Beside those analyses, we extract $\alpha$
through the use of several adequate parametrizations, showing that there is no
relevant discrepancy between frequentist and bayesian results. The most
relevant information, in terms of $\alpha$, is the exclusion of values around
$\alpha\sim \pi/4$; this result is valid in the presence of arbitrary New
Physics contributions to the $\Delta I=1/2$ piece.
|
Solar System Constraints on Gauss-Bonnet Mediated Dark Energy | Although the Gauss-Bonnet term is a topological invariant for general
relativity, it couples naturally to a quintessence scalar field, modifying
gravity at solar system scales. We determine the solar system constraints due
to this term by evaluating the post-Newtonian metric for a distributional
source. We find a mass dependent, 1/r^7 correction to the Newtonian potential,
and also deviations from the Einstein gravity prediction for light-bending. We
constrain the parameters of the theory using planetary orbits, the Cassini
spacecraft data, and a laboratory test of Newton's law, always finding
extremely tight bounds on the energy associated to the Gauss-Bonnet term. We
discuss the relevance of these constraints to late-time cosmological
acceleration.
|
Switching mechanism of photochromic diarylethene derivatives molecular
junctions | The electronic transport properties and switching mechanism of single
photochromic diarylethene derivatives sandwiched between two gold surfaces with
closed and open configurations are investigated by a fully self-consistent
nonequilibrium Green's function method combined with density functional theory.
The calculated transmission spectra of two configurations are strikingly
distinctive. The open form lacks any significant transmission peak within a
wide energy window, while the closed structure has two significant transmission
peaks on the both sides of the Fermi level. The electronic transport properties
of the molecular junction with closed structure under a small bias voltage are
mainly determined by the tail of the transmission peak contributed unusually by
the perturbed lowest perturbed unoccupied molecular orbital. The calculated
on-off ratio of currents between the closed and open configurations is about
two orders of magnitude, which reproduces the essential features of the
experimental measured results. Moreover, we find that the switching behavior
within a wide bias voltage window is extremely robust to both substituting F or
S for H or O and varying end anchoring atoms from S to Se and Te.
|
Robust manipulation of electron spin coherence in an ensemble of singly
charged quantum dots | Using the recently reported mode locking effect we demonstrate a highly
robust control of electron spin coherence in an ensemble of (In,Ga)As quantum
dots during the single spin coherence time. The spin precession in a transverse
magnetic field can be fully controlled up to 25 K by the parameters of the
exciting pulsed laser protocol such as the pulse train sequence, leading to
adjustable quantum beat bursts in Faraday rotation. Flipping of the electron
spin precession phase was demonstrated by inverting the polarization within a
pulse doublet sequence.
|
Equation of state for dense hydrogen and plasma phase transition | We calculate the equation of state of dense hydrogen within the chemical
picture. Fluid variational theory is generalized for a multi-component system
of molecules, atoms, electrons, and protons. Chemical equilibrium is supposed
for the reactions dissociation and ionization. We identify the region of
thermodynamic instability which is related to the plasma phase transition. The
reflectivity is calculated along the Hugoniot curve and compared with
experimental results. The equation-of-state data is used to calculate the
pressure and temperature profiles for the interior of Jupiter.
|
Experimental nonclassicality of single-photon-added thermal light states | We report the experimental realization and tomographic analysis of novel
quantum light states obtained by exciting a classical thermal field by a single
photon. Such states, although completely incoherent, possess a tunable degree
of quantumness which is here exploited to put to a stringent experimental test
some of the criteria proposed for the proof and the measurement of state
non-classicality. The quantum character of the states is also given in quantum
information terms by evaluating the amount of entanglement that they can
produce.
|
Neutron Skin and Giant Resonances in Nuclei | Some aspects, both experimental and theoretical, of extracting the neutron
skin $\Delta R$ from properties of isovector giant resonances are discussed.
Existing proposals are critically reviewed. The method relying on the energy
difference between the GTR and IAS is shown to lack sensitivity to $\Delta R$.
A simple explanation of the linear relation between the symmetry energy and the
neutron skin is also given.
|
Genetic Optimization of Photonic Bandgap Structures | We investigate the use of a Genetic Algorithm (GA) to design a set of
photonic crystals (PCs) in one and two dimensions. Our flexible design
methodology allows us to optimize PC structures which are optimized for
specific objectives. In this paper, we report the results of several such
GA-based PC optimizations. We show that the GA performs well even in very
complex design spaces, and therefore has great potential for use as a robust
design tool in present and future applications.
|
Huge magneto-crystalline anisotropy of x-ray linear dichroism observed
on Co/FeMn bilayers | We present an x-ray spectromicroscopic investigation of single-crystalline
magnetic FeMn/Co bilayers on Cu(001), using X-ray magnetic circular (XMCD) and
linear (XMLD) dichroism at the Co and Fe L3 absorption edges in combination
with photoelectron emission microscopy (PEEM). Using the magnetic coupling
between the ferromagnetic Co layer and the antiferromagnetic FeMn layer we are
able to produce magnetic domains with two different crystallographic
orientations of the magnetic easy axis within the same sample at the same time.
We find a huge difference in the XMLD contrast between the two types of
magnetic domains, which we discuss in terms of intrinsic magneto-crystalline
anisotropy of XMLD of the Co layer. We also demonstrate that due to the high
sensitivity of the method, the small number of induced ferromagnetic Fe moments
at the FeMn-Co interface is sufficient to obtain magnetic contrast from XMLD in
a metallic system.
|
Temperature Dependence of the Tensile Properties of Single Walled Carbon
Nanotubes: O(N) Tight Binding MD Simulation | This paper examines the effect of temperature on the structural stability and
mechanical properties of 20 layered (10,10) single walled carbon nanotubes
(SWCNTs) under tensile loading using an O(N) tight binding molecular dynamics
(TBMD) simulation method. We observed that (10,10) tube can sustain its
structural stability for the strain values of 0.23 in elongation and 0.06 in
compression at 300K. Bond breaking strain value decreases with increasing
temperature under streching but not under compression. The elastic limit,
Young's modulus, tensile strength and Poisson ratio are calculated as 0.10,
0.395 TPa, 83.23 GPa, 0.285, respectively, at 300K. In the temperature range
from 300K to 900K; Young's modulus and the tensile strengths are decreasing
with increasing temperature while the Poisson ratio is increasing. At higher
temperatures, Young's modulus starts to increase while the Poisson ratio and
tensile strength decrease. In the temperature range from 1200K to 1800K, the
SWCNT is already deformed and softened. Applying strain on these deformed and
softened SWCNTs do not follow the same pattern as in the temperature range of
300K to 900K.
|
Gamma-ray emitting AGN and GLAST | I describe the different classes of Active Galactic Nuclei (AGN) and the
basic tenets of unified schemes. I then review the properties of the
extragalactic sources detected in the GeV and TeV bands, showing that the vast
majority of them belong to the very rare blazar class. I further discuss the
kind of AGN GLAST is likely to detect, making some predictions going from the
obvious to the likely, all the way to the less probable.
|
Potfit: effective potentials from ab-initio data | We present a program called potfit which generates an effective atomic
interaction potential by matching it to a set of reference data computed in
first-principles calculations. It thus allows to perform large-scale atomistic
simulations of materials with physically justified potentials. We describe the
fundamental principles behind the program, emphasizing its flexibility in
adapting to different systems and potential models, while also discussing its
limitations. The program has been used successfully in creating effective
potentials for a number of complex intermetallic alloys, notably quasicrystals.
|
Dark energy and neutrino model in SUSY -- Remarks on active and sterile
neutrinos mixing -- | We consider a Mass Varying Neutrinos (MaVaNs) model in supersymmetric theory.
The model includes effects of supersymmetry breaking transmitted by the
gravitational interaction from the hidden sector, in which supersymmetry was
broken, to the dark energy sector. Then evolutions of the neutrino mass and the
equation of state parameter of the dark energy are presented in the model. It
is remarked that only the mass of a sterile neutrino is variable in the case of
the vanishing mixing between the left-handed and a sterile neutrino on
cosmological time scale. The finite mixing makes the mass of the left-handed
neutrino variable.
|
The transverse proximity effect in spectral hardness on the line of
sight towards HE 2347-4342 | We report the discovery of 14 quasars in the vicinity of HE2347-4342, one of
the two quasars whose intergalactic HeII forest has been resolved with FUSE. By
analysing the HI and the HeII opacity variations separately, no transverse
proximity effect is detected near three foreground quasars of HE2347-4342:
QSOJ23503-4328 (z=2.282, $\vartheta=3.59$ arcmin), QSOJ23500-4319 (z=2.302,
$\vartheta=8.77$ arcmin) and QSOJ23495-4338 (z=2.690, $\vartheta=16.28$
arcmin). This is primarily due to line contamination and overdensities probably
created by large-scale structure. By comparing the HI absorption and the
corresponding HeII absorption, we estimated the fluctuating spectral shape of
the extragalactic UV radiation field along this line of sight. We find that the
UV spectral shape near HE2347-4342 and in the projected vicinity of the three
foreground quasars is statistically harder than expected from UV background
models dominated by quasars. In addition, we find three highly ionised metal
line systems near the quasars. However, they do not yield further constraints
on the shape of the ionising field. We conclude that the foreground quasars
show a transverse proximity effect that is detectable as a local hardening of
the UV radiation field, although the evidence is strongest for QSOJ23495-4338.
Thus, the relative spectral hardness traces the proximity effect also in
overdense regions prohibiting the traditional detection in the HI forest.
Furthermore, we emphasise that softening of quasar radiation by radiative
transfer in the intergalactic medium is important to understand the observed
spectral shape variations. From the transverse proximity effect of
QSOJ23495-4338 we obtain a lower limit on the quasar lifetime of ~25 Myr.
|
Biased random walks on combs | We develop rigorous, analytic techniques to study the behaviour of biased
random walks on combs. This enables us to calculate exactly the spectral
dimension of random comb ensembles for any bias scenario in the teeth or spine.
Two specific examples of random comb ensembles are discussed; the random comb
with nonzero probability of an infinitely long tooth at each vertex on the
spine and the random comb with a power law distribution of tooth lengths. We
also analyze transport properties along the spine for these probability
measures.
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Monoid generalizations of the Richard Thompson groups | The groups G_{k,1} of Richard Thompson and Graham Higman can be generalized
in a natural way to monoids, that we call M_{k,1}, and to inverse monoids,
called Inv_{k,1}; this is done by simply generalizing bijections to partial
functions or partial injective functions. The monoids M_{k,1} have connections
with circuit complexity (studied in another paper). Here we prove that M_{k,1}
and Inv_{k,1} are congruence-simple for all k. Their Green relations J and D
are characterized: M_{k,1} and Inv_{k,1} are J-0-simple, and they have k-1
non-zero D-classes. They are submonoids of the multiplicative part of the Cuntz
algebra O_k. They are finitely generated, and their word problem over any
finite generating set is in P. Their word problem is coNP-complete over certain
infinite generating sets.
Changes in this version: Section 4 has been thoroughly revised, and errors
have been corrected; however, the main results of Section 4 do not change.
Sections 1, 2, and 3 are unchanged, except for the proof of Theorem 2.3, which
was incomplete; a complete proof was published in the Appendix of reference
[6], and is also given here.
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The Reliability on the Direction of the Incident Neutrino for the Fully
Contained Events and Partially Contained Events due to QEL in the
Super-Kamiokande | In the SK analysis of the neutrino events for [Fully Contained Events] and
[Partially Contained Events] on their zenith angle distribution, it is assumed
that the zenith angle of the incident neutrino is the same as that of the
detected charged lepton. In the present paper, we examine the validity of [the
SK assumption on the direction] of the incident neutrinos. Concretely speaking,
we analyze muon-like events due to QEL. For the purpose, we develop [Time
Sequential Monte Carlo Simulation] to extract the conclusion on the validity of
the SK assumption. In our [Time Sequential Simulation], we simulate every
physical process concerned as exactly as possible without any approximation.
From the comparison between the zenith angle distributon of the emitted muons
under [the SK assumption on the direction] and the corresponding one obtained
under our [Time Sequential Simulation], it is concluded that the measurement of
the direction of the incident neutrino for the neutrino events occurring inside
the detector in the SK analysis turns out to be unreliable, which holds
irrespective of the existence and/or non-existence of the neutrino oscillation.
|
Intricate Knots in Proteins: Function and Evolution | A number of recently discovered protein structures incorporate a rather
unexpected structural feature: a knot in the polypeptide backbone. These knots
are extremely rare, but their occurrence is likely connected to protein
function in as yet unexplored fashion. Our analysis of the complete Protein
Data Bank reveals several new knots which, along with previously discovered
ones, can shed light on such connections. In particular, we identify the most
complex knot discovered to date in human ubiquitin hydrolase, and suggest that
its entangled topology protects it against unfolding and degradation by the
proteasome. Knots in proteins are typically preserved across species and
sometimes even across kingdoms. However, we also identify a knot which only
appears in some transcarbamylases while being absent in homologous proteins of
similar structure. The emergence of the knot is accompanied by a shift in the
enzymatic function of the protein. We suggest that the simple insertion of a
short DNA fragment into the gene may suffice to turn an unknotted into a
knotted structure in this protein.
|
Star Formation in Galaxies with Large Lower Surface Brightness Disks | We present B, R, and Halpha imaging data of 19 large disk galaxies whose
properties are intermediate between classical low surface brightness galaxies
and ordinary high surface brightness galaxies. We use data taken from the
Lowell 1.8m Perkins telescope to determine the galaxies' overall morphology,
color, and star formation properties. Morphologically, the galaxies range from
Sb through Irr and include galaxies with and without nuclear bars. The colors
of the galaxies vary from B-R = 0.3 - 1.9, and most show at least a slight
bluing of the colors with increasing radius. The Halpha images of these
galaxies show an average star formation rate lower than is found for similar
samples with higher surface brightness disks. Additionally, the galaxies
studied have both higher gas mass-to-luminosity and diffuse Halpha emission
than is found in higher surface brightness samples.
|
Domain Wall Dynamics near a Quantum Critical Point | We study the real-time domain-wall dynamics near a quantum critical point of
the one-dimensional anisotropic ferromagnetic spin 1/2 chain. By numerical
simulation, we find the domain wall is dynamically stable in the
Heisenberg-Ising model. Near the quantum critical point, the width of the
domain wall diverges as $(\Delta -1) ^{-1/2}$.
|
Quantum mechanical approach to decoherence and relaxation generated by
fluctuating environment | We consider an electrostatic qubit, interacting with a fluctuating charge of
single electron transistor (SET) in the framework of exactly solvable model.
The SET plays a role of the fluctuating environment affecting the qubit's
parameters in a controllable way. We derive the rate equations describing
dynamics of the entire system for both weak and strong qubit-SET coupling.
Solving these equation we obtain decoherence and relaxation rates of the qubit,
as well as the spectral density of the fluctuating qubit's parameters. We found
that in the weak coupling regime the decoherence and relaxation rates are
directly related to the spectral density taken at Rabi or at zero frequency,
depending on what a particular qubit's parameters is fluctuating. This relation
holds also in the presence of weak back-action of the qubit on the fluctuating
environment. In the case of strong back-action, such simple relationship no
longer holds, even if the qubit-SET coupling is small. It does not hold either
in the strong-coupling regime, even in the absence of the back-action. In
addition, we found that our model predicts localization of the qubit in the
strong-coupling regime, resembling that of the spin-boson model.
|
Group-theoretical properties of nilpotent modular categories | We characterize a natural class of modular categories of prime power
Frobenius-Perron dimension as representation categories of twisted doubles of
finite p-groups. We also show that a nilpotent braided fusion category C admits
an analogue of the Sylow decomposition. If the simple objects of C have
integral Frobenius-Perron dimensions then C is group-theoretical. As a
consequence, we obtain that semisimple quasi-Hopf algebras of prime power
dimension are group-theoretical. Our arguments are based on a reconstruction of
twisted group doubles from Lagrangian subcategories of modular categories (this
is reminiscent to the characterization of doubles of quasi-Lie bialgebras in
terms of Manin pairs).
|
Remarks on N_c dependence of decays of exotic baryons | We calculate the N_c dependence of the decay widths of exotic eikosiheptaplet
within the framework of Chral Quark Soliton Model. We also discuss
generalizations of regular baryon representations for arbitrary N_c.
|
Analysis of random Boolean networks using the average sensitivity | In this work we consider random Boolean networks that provide a general model
for genetic regulatory networks. We extend the analysis of James Lynch who was
able to proof Kauffman's conjecture that in the ordered phase of random
networks, the number of ineffective and freezing gates is large, where as in
the disordered phase their number is small. Lynch proved the conjecture only
for networks with connectivity two and non-uniform probabilities for the
Boolean functions. We show how to apply the proof to networks with arbitrary
connectivity $K$ and to random networks with biased Boolean functions. It turns
out that in these cases Lynch's parameter $\lambda$ is equivalent to the
expectation of average sensitivity of the Boolean functions used to construct
the network. Hence we can apply a known theorem for the expectation of the
average sensitivity. In order to prove the results for networks with biased
functions, we deduct the expectation of the average sensitivity when only
functions with specific connectivity and specific bias are chosen at random.
|
Theory of polariton mediated Raman scattering in microcavities | We calculate the intensity of the polariton mediated inelastic light
scattering in semiconductor microcavities. We treat the exciton-photon coupling
nonperturbatively and incorporate lifetime effects in both excitons and
photons, and a coupling of the photons to the electron-hole continuum. Taking
the matrix elements as fitting parameters, the results are in excellent
agreement with measured Raman intensities due to optical phonons resonant with
the upper polariton branches in II-VI microcavities with embedded CdTe quantum
wells.
|
Decomposition numbers for finite Coxeter groups and generalised
non-crossing partitions | Given a finite irreducible Coxeter group $W$, a positive integer $d$, and
types $T_1,T_2,...,T_d$ (in the sense of the classification of finite Coxeter
groups), we compute the number of decompositions $c=\si_1\si_2 cdots\si_d$ of a
Coxeter element $c$ of $W$, such that $\si_i$ is a Coxeter element in a
subgroup of type $T_i$ in $W$, $i=1,2,...,d$, and such that the factorisation
is "minimal" in the sense that the sum of the ranks of the $T_i$'s,
$i=1,2,...,d$, equals the rank of $W$. For the exceptional types, these
decomposition numbers have been computed by the first author. The type $A_n$
decomposition numbers have been computed by Goulden and Jackson, albeit using a
somewhat different language. We explain how to extract the type $B_n$
decomposition numbers from results of B\'ona, Bousquet, Labelle and Leroux on
map enumeration. Our formula for the type $D_n$ decomposition numbers is new.
These results are then used to determine, for a fixed positive integer $l$ and
fixed integers $r_1\le r_2\le ...\le r_l$, the number of multi-chains $\pi_1\le
\pi_2\le ...\le \pi_l$ in Armstrong's generalised non-crossing partitions
poset, where the poset rank of $\pi_i$ equals $r_i$, and where the "block
structure" of $\pi_1$ is prescribed. We demonstrate that this result implies
all known enumerative results on ordinary and generalised non-crossing
partitions via appropriate summations. Surprisingly, this result on multi-chain
enumeration is new even for the original non-crossing partitions of Kreweras.
Moreover, the result allows one to solve the problem of rank-selected chain
enumeration in the type $D_n$ generalised non-crossing partitions poset, which,
in turn, leads to a proof of Armstrong's $F=M$ Conjecture in type $D_n$.
|
Electromagnetic polarizabilities and the excited states of the nucleon | The electromagnetic polarizabilities of the nucleon are shown to be
essentially composed of the nonresonant $\alpha_p(E_{0+})=+3.2$,
$\alpha_n(E_{0+})=+4.1$,the $t$-channel $\alpha^t_{p,n}=-\beta^t_{p,n}=+7.6$
and the resonant $\beta_{p,n}(P_{33}(1232))=+8.3$ contributions (in units of
$10^{-4}$fm$^3$. The remaining deviations from the experimental data
$\Delta\alpha_p=1.2\pm 0.6$, $\Delta\beta_p=1.2\mp 0.6$, \Delta\alpha_n=0.8\pm
1.7$ and $\Delta\beta_n=2.0\mp 1.8$ are contributed by a larger number of
resonant and nonresonant processes with cancellations between the
contributions. This result confirms that dominant contributions to the electric
and magnetic polarizabilities may be represented in terms of two-photon
couplings to the $\sigma$-meson having the predicted mass $m_\sigma=666$ MeV
and two-photon width $\Gamma_{\gamma\gamma}=2.6$ keV.
|