bluuebunny/crossref_metadata_2025 huggingface dataset:
TWISTOR GEOMETRY, SPINOR STRUCTURE AND NATURE OF SUPERSPACE
Authors: BANDYOPADHYAY PRATUL , GHOSH PRADIP
Published: November 2004

The nature of superspace is studied here from the viewpoint of eight-component conformal spinors which can be split into two Cartan semispinors having two internal helicities corresponding to particle and anti-particle states. This leads to the generation of internal symmetry through reflection group. It is shown that each member of the doublet can be taken to behave as twistors in complexified Minkowski space-time. This helps us to introduce a spinor structure at each space-time point and the spinor coordinate gives rise to the internal helicity. This may be achieved through the introduction of a direction vector attached to each space-time point. Superspace here appears as a bundle space where the base space is the ordinary Minkowski space-time and the spinorial coordinates generated through the introduction of the direction vector from the fibre. This suggests that the internal space of hadrons is anisotropic in nature.
QUANTUM CORRECTIONS EFFECT ON THE COUPLING OF THE GRAVITATIONAL AND SCALAR FIELDS AND SPONTANEOUSLY INDUCED GRAVITY
Authors: KAGANOVICH A. B.
Published: November 2004

Gravity induced by the spontaneous symmetry breaking in gauge theories is studied. All calculations are carried out with an accuracy provided by the one-loop approximation. It appears that in an effective potential of the scalar field φ a parameter ε of a nonminimal coupling of φ with a curvature is a function of φ. Under zero energy density of the stable vacuum <φ>0 = µ it is proved that the induced gravitational constant G ind is finite only if µε′(µ) = −2ε(µ). Hence it follows that if gravity is induced indeed then its theory necessarily has the structure of the Einstein's theory for gravitation: G ind is positive and invariable (at zero temperature). Within the limitations imposed by the model, the T-dependence of G ind is exponentially relaxed.
A UNIFIED APPROACH TO THE COMPUTATION OF CENTRAL TERMS IN KAC-MOODY AND VIRASORO ALGEBRAS
Authors: GORMAN N. , O'RAIFEARTAIGH L. , WILLIAMS D. , McGLINN W.
Published: November 2004

A theorem is established which gives a unified formula for the commutator of two bilinear Kac-Moody (KM) or Virasoro (V) currents in terms of these currents and a central term. The formula not only covers the standard bilinear cases previously considered (V currents of matter, string, ghost and KM fields, and KM currents of free fields) but also the two twisted cases, namely the V currents of twisted KM fields and twisted KM currents of free fields. It is also shown that in BRST theory the central term C is always the Hessian of the BRST charge Q2 (which explains the well-known equivalence of C = 0 and Q2 = 0).
BOUND STATES OF QUARKS TO ISOSPIN BALLS
Authors: BOURDEAU M. , SRIVASTAVA A.M.
Published: November 2004

Balachandran et al. have shown that nontopological solitons exist in a class of chiral models which incorporate scale anomaly. We have shown that bound states of quarks and antiquarks to these solitons exist. Masses of low-lying baryonic and mesonic bound states are estimated in the collective coordinate approximation.
PARTICLE PRODUCTION AT COLLIDER ENERGIES
Authors: GEICH-GIMBEL CHRISTOPH
Published: November 2004

High energy particle physics, which has been trying to understand and to devise new laws governing nature at per particle energies far beyond everyday energies, has entered a new episode.

Having surpassed the ‘low energy’ regime, where (s channel) resonance production dominantly projects onto the final state, very interesting features of the strong interaction arose at c.m. energies in the tens of GEV range, as found at the CERN Intersecting Storage Rings (ISR).

One recalls the onset of hard scattering processes, which was understood as a scattering between constituents of the nucleon, hence supporting the Quark Parton Model (QPM). Surprisingly enough the total cross section started to rise again, when it was initially believed to have reached a constant value, suggesting an asymptotia. Furthermore correlations among the final state particles produced were observed, and especially long range correlations, which must reflect dynamical laws.

The advent of the CERN [Formula: see text] Collider, with c.m. energies up to 900 GeV, representing a step of more than an order of magnitude in the energy available, puts one into a position to test more directly many of these ‘new’ things and to prove the existence of the elusive intermediate vector bosons W± and Z, thus unifying weak and electromagnetic interactions. Finally a bridge to cosmic ray results at extreme energies may be provided.

Naturally quite a lot of new unanswered questions will emerge in the investigations of Collider data, since new regions bring new surprises, but this possibility should be regarded as a means of gaining new insights, rather than as a disturbance of hitherto believed regularities, of which some inevitably fail.

In this spirit the following article is written.
A NOTE ON MANY-LOOP CALCULATIONS FOR SUPERSTRINGS IN THE NSR FORMALISM
Authors: MOROZOV A. , PERELOMOV A.
Published: November 2004

A rather simple and attractive prescription for many-loop calculations is discussed. It consists of specification of metric, super-Beltrami differentials and the sum over spin structures in terms of the same odd characteristic e*. At the end of the calculations, summation over e* is performed in order to restore modular invariance. We note that this prescription should include specification of the limiting procedure involved. For a special choice of “regularization” the contributions of matter supercurrents to cosmological constant vanish at least for p≤5.
QCD JETS AT HERA I.: O(αs) RADIATIVE CORRECTIONS TO ELECTROWEAK CROSS SECTIONS AND JET RATES
Authors: KÖRNER JÜRGEN G. , MIRKES ERWIN , SCHULER GERHARD A.
Published: November 2004

We present the complete O(αs) corrections to the electroweak cross sections of both neutral current and charged current deep inelastic e±p scattering including lepton polarization effects. Changes in the cross section due to the inclusion of next-to-leading-log (NLL) effects are parametrized by K factors, which are defined as the ratio of the NLL O(αs) cross sections and the Born cross section. Using the standard redefinition scheme of the parton densities, we find that the K factors deviate substantially from unity for small values of the Bjorken-Scaling variable x. We also elaborate on problems that arise when defining jet cross sections in ep scattering and present numerical results for the O(αs) 3-jet and 2-jet rates. We observe that the Q2-dependence of the 3-jet rate is dominated by the running strong coupling constant αs(Q2) allowing for its determination over a wide range in Q2 at high energy ep colliders.
THE ULTRAVIOLET PROPERTIES OF SUPERSYMMETRIC FIELD THEORIES
Authors: HOWE P. S. , STELLE K. S.
Published: November 2004

We review the structure of ultraviolet divergence cancellations in supersymmetric field theories. We discuss the various nonrenormalization theorems of superspace perturbation theory, both for extended and for simple supersymmetry. These theorems and the background field method are applied to super Yang-Mills theories in four and higher dimensions, to supergravity theories and to two-dimensional supersymmetric nonlinear σ-models.
GRAVITATIONAL CURVATURES IN 4D CONFORMAL SUPERGRAVITY
Authors: PASQUINUCCI ANDREA , PENATI SILVIA
Published: November 2004

In this paper we compute all the components of the superconformal gravitational curvature multiplets of D=4N=1 supergravity; a linear matter multiplet is used to define the superconformal covariant derivatives. In this formulation, we prove also the super Gauss-Bonnet theorem.
THE POMERON INTERCEPT REVISITED
Authors: ZERNER MARTIN
Published: November 2004

We study the lattice approximation to Reggeon Field Theory. An approximate computation of the renormalized Pomeron intercept is proposed and shows that it is equal to one as required for the theory to be consistent with experimental results and with Froissart’s bound. A stricter derivation of this requirement is also given. At fixed impact parameter the cross section seems to be asymptotically bounded.
PERTURBATIVE SOLUTION TO THE BACK REACTION PROBLEM FOR STATIC BLACK HOLES
Authors: LOUSTÓ C.O. , SÁNCHEZ N.
Published: November 2004

Using Israel’s description of static space-times with event horizons, we give a general (2+2) formulation of semiclassical Einstein equations in four dimensions in terms of two-dimensional quantities. We find analytic expressions for the metric coefficients in the spherically symmetric case and in a perturbative scheme (taking Schwarzschild’s metric as a zero order solution and the perturbation parameters Mpl/M, Mpl and M being the planck and black hole masses respectively). Modifications to the horizon radius, Hawking temperature, luminosity and lifetime of evaporating black holes are found due to the back reaction. Two different situations appear depending on the graviton-matter balance. If matter is relevant, the temperature is increased and thus the lifetime decreased from their standard values TH=1/8πM and τH=CM3. If graviton is dominant T is smaller than TH and, more important, it can have a maximum at M~Mpl and then go to zero. The connection with string theory is discussed.
AN ELECTROWEAK FACTORIZATION THEOREM
Authors: LAKSHMIBALA S. , RAJASEKARAN G.
Published: November 2004

We prove a factorization property relating the photon exchange, the Z boson exchange and the electroweak interference terms of the differential cross-section for the process fermion+ antifermion→bosons occurring through the exchange of a single photon and a single Z boson. The property holds at tree-level when the bosons are unpolarized or linearly polarized and the fermions are unpolarized or longitudinally polarized. We have illustrated the factorization property with examples in the standard electroweak theory as well as its extensions and modifications.
A COMPREHENSIVE INTRODUCTION TO THE LAGEOS GRAVITOMAGNETIC EXPERIMENT: FROM THE IMPORTANCE OF THE GRAVITOMAGNETIC FIELD IN PHYSICS TO PRELIMINARY ERROR ANALYSIS AND ERROR BUDGET
Authors: CIUFOLINI IGNAZIO
Published: November 2004

The existence of the gravitomagnetic field. generated by mass currents according to Einstein geometrodynamics, has never been proved. The author of this paper, after a discussion of the importance of the gravitomagnetic field in physics, describes the experiment that he proposed in 1984 to measure this field using LAGEOS (Laser geodynamics satellite) together with another non-polar, laser-ranged satellite with the same orbital parameters as LAGEOS but a supplementary inclination.

The author then studies the main perturbations and measurement uncertainties that may affect the measurement of the Lense-Thirring drag. He concludes that, over the period of the node of ~3 years, the maximum error, using two nonpolar laser ranged satellites with supplementary inclinations, should not be larger than ~10% of the gravitomagnetic effect to be measured.
GLUON PRODUCTION AMPLITUDES FOR $q\bar{q}$ HIGH ENERGY BACKWARD SCATTERING
Authors: ERMOLAEV B.I. , LIPATOV L.N.
Published: November 2004

A factorization method is used for the investigation of gluon bremsstrahlung in the quark-antiquark backward scattering. The differential equations for scattering amplitudes are obtained in a double-logarithmic approximation. These equations are solved for some cases of interest.
GAUGE INVARIANCE AND CONSTRAINTS
Authors: PYATOV P.N. , RAZUMOV A.V.
Published: November 2004

It is shown that in the Hamiltonian description of a wide class of gauge invariant Lagrangian systems there arise only primary and secondary constraints and they are all first class. The explicit expressions for the Poisson brackets of the Hamiltonian and the constraints are obtained by introducing the so-called “standard” extension of functions originally defined on the primary constraint surface to the whole phase space.
TRANSVERSE ENERGY PRODUCTION IN LIGHT AND HEAVY ION INTERACTIONS
Authors: TANNENBAUM M.J.
Published: November 2004

Transverse energy distributions have proved to be useful in the understanding of reaction mechanisms of relativistic heavy ion interactions. The development of the subject is traced from its roots in elementary particle physics. A review and analysis of the data from recent measurements in high energy heavy ion beams at CERN and Brookhaven is presented.
ABELIZED VIRASORO OPERATORS, GEOMETRY AND THE STRING VERTEX OPERATOR
Authors: ARATYN HENRIK , INGERMANSON RANDALL
Published: November 2004

In this article, we review recent work on constrained Hamiltonian systems with infinite-dimensional constraint algebras. The work is based on an extension of the constraint algebra to include subsidiary (gauge-fixing) constraints and a central element, forming a larger, closed algebra. This extension leads to several immediate results, at both a practical and a conceptual level: 1) A simple method is found for abelizing the original constraints. 2) This leads naturally to a “generalized vielbein” relating Abelian and non-Abelian quantities. 3) The vielbein apparatus makes transparent the full global symmetry of the extended phase space associated with the Batalin, Fradkin and Vilkovisky formalism. An interesting duality also arises between quantities with “Abelian” and “non-Abelian” indices.

String theory provides the most important and straightforward application of these general methods. For this special case, one finds that the vielbeins are the Fourier components of the string vertex operator. The vertex operator describes the physical process of photon emission, and determines the physical modes of the string by way of the DDF operators. Due to the relation between the vertex operator and the vielbein, the dual abelized Virasoro operators simplify the usual discussion of the physical Fock space. The correspondence between these two fundamental objects, the vertex and the vielbein, thus provides a geometric understanding of the usual algebraic approach to string theory.
ON THE DECAY OF A HEAVY HIGGS BOSON INTO Z+LEPTON PAIR IN E6 SUPERSTRING MODELS
Authors: PÓCSIK G. , TORMA T.
Published: November 2004

We calculate the width (Γ) and differential energy distributions of [Formula: see text] in E6-based models containing one extra U(1). For a fixed Z′ mass, Γ is strongly growing with increasing mH, while for a fixed mH it decreases strongly with increasing mz′. The energy distribution of Z has a pronounced maximum tending to larger energies of Z with increasing mH, for a fixed mz′. In certain parameter ranges, Γ is larger than the width of the [Formula: see text] decay mode.
RELATION BETWEEN BATALIN-VILKOVISKY AND FIRST-QUANTIZED- STYLE BRST
Authors: SIEGEL W.
Published: November 2004

We show that first-quantized-style Becchi-Rouet-Stora-Tyutin operators, such as those which occur in string field theory, are just those of the Batalin-Vilkovisky method, up to some minor modifications. Thus, string field theory can be quantized directly, without fields additional to the original one.
BRST-FORMULATION OF A MASSLESS SPIN-1 PARTICLE
Authors: DOMEIJ THOMAS
Published: November 2004

We present a detailed calculation of BRST quantization of a free massless spin-1 particle. Then we go on to describe a field theory, inspired by Witten's string field theory, in an attempt to also include interactions.
TWO-LOOP COMPUTATIONS IN SUPERSTRING THEORIES
Authors: ZHU CHUAN-JIE
Published: November 2004

We give in this paper the full details of the computations in superstring theories at two-loops. Some mathematics about hyperelliptic surface are also included.
LANDAU LEVELS AND GEOMETRIC QUANTIZATION
Authors: KLAUDER J. R. , ONOFRI E.
Published: November 2004

The geometrical approach to phase-space quantization introduced by Klauder [KQ] is interpreted in terms of a universal magnetic field acting on a free particle moving in a higher dimensional configuration space; quantization corresponds to freezing the particle to its first Landau level. The Geometric Quantization [GQ] scheme appears as the natural technique to define the interaction with the magnetic field for a particle on a general Riemannian manifold. The freedom of redefining the operators' ordering makes it possible to select that particular definition of the Hamiltonian which is adapted to a specific polarization; in this way the first Landau level acquires the expected degeneracy. This unification with GQ makes it clear how algebraic relations between classical observables are or are not preserved under quantization. From this point of view all quantum systems appear as the low energy sector of a generalized theory in which all classical observables have a uniquely assigned quantum counterpart such that Poisson bracket relations are isomorphic to the commutation relations.
BATALIN-VILKOVISKY FROM HAMILTONIAN BRST
Authors: SIEGEL W.
Published: November 2004

We derive the Batalin-Vilkovisky form of the Becchi-Rouet-Stora-Tyutin operator from the Hamiltonian form. In the case of the string in the conformal gauge, the world-sheet metric reappears as the antifield of the antighost.
UNDERSTANDING FUJIKAWA REGULATORS FROM PAULI-VILLARS REGULARIZATION OF GHOST LOOPS
Authors: DIAZ A. , TROOST W. , VAN NIEUWENHUIZEN P. , Van PROEYEN A.
Published: November 2004

We construct mass terms for the ghost and antighost in the bosonic string which preserve coordinate BRST invariance. This allows us to compute the Weyl and ghost number anomalies with Pauli-Villars regularization. An algorithm is derived for the construction of those regulators in the Fujikawa scheme which yield consistent anomalies. In the formulation with the BRST auxiliary fields we find that the nonpropagating two-dimensional gravitational field must be regulated in the same way as the antighost. It contributes the same amount to the anomaly as the antighosts do when one eliminates the auxiliary fields.
DIQUARKS IN ELEMENTARY PARTICLE PHYSICS
Authors: SZCZEKOWSKI MAREK
Published: November 2004

Many phenomena in elementary particle physics show indications of clustering of two quarks inside baryons. Although the existence of such diquark systems cannot be presently rigorously proven in quantum field theory of strong interactions, phenomenological models require some quark-quark binding to explain effects ranging from the baryon mass spectrum to large pT proton production in high energy pp collisions. This review confronts diquark models predictions with experimental results in low and high transverse momentum hadron-hadron collisions, lepton-nucleon scattering and e+e− annihilations. The recent data from the Split Field Magnet detector on high pT proton production in pp, dd and αα collisions at ISR energies are particularly emphasized.
INTEGRALS OF MOTION AND S-MATRIX OF THE (SCALED) T = Tc ISING MODEL WITH MAGNETIC FIELD
Authors: ZAMOLODCHIKOV A. B.
Published: November 2004

It is shown that the field theory describing the scaling limit of T = T c Ising model with nonzero magnetic field possesses a number of nontrivial local integrals of motion. The exact mass spectrum and S-matrix of this field theory is conjectured.
KRICHEVER — NOVIKOV BASES FOR THE BOSONIC STRING
Authors: LEE TAEJIN , VISWANATHAN K. S.
Published: November 2004

The global operator formalism proposed recently by Krichever and Novikov using meromorphic tensor fields on general Riemann surfaces of arbitrary genus is applied to the bosonic string. The well-known Green's function of the scalar boson fields is obtained in a simple manner from the spectral representation. Proof of Wick's theorem is also given.
VECTOR-SPINOR SUPERALGEBRA AND GOLDSTONE SPIN −3/2 FERMIONS
Authors: PILOT CHRISTOPHER , RAJPOOT SUBHASH
Published: November 2004

The super-Poincare algebra of the generators belonging to the irreducible (1, 1/2) + (1/2, 1) representation of the Lorentz group is constructed. It is shown that the nonlinear realizations of the vector spinor superalgebra lead to a goldstone fermion carrying spin −3/2. A phenomenological Lagrangian is constructed that describes interactions of the spin −3/2 goldstone fermion with itself.
NUCLEAR PHOTOABSORPTION IN 208Pb BETWEEN THRESHOLD AND 140 MeV
Authors: QUARATI P. , DELSANTO P. P. , GUIDETTI M.
Published: November 2004

We have investigated photonuclear reactions in 208 Pb from the reaction threshold to pion production threshold. In the Giant Dipole Resonance energy region we have considered the results of a recent 1− 1p-1h continuum calculation and multiplied them, heuristically, by a factor, which includes the effect of neglected nucleon-nucleon correlations, through the occupation number probabilities of the single particle and hole energy levels. We have thus obtained a much better agreement with experiment. In the energy region above the Giant Dipole Resonance we have considered a quasi deuteron model, which contains the effect of nucleon swelling. Both this model and corresponding integrated sum rules yield a satisfactory agreement with experiment.
SEARCH FOR ANOMALOUS Z = 2 FRAGMENTS FROM 12C EMULSION INTERACTIONS AT 4.5 A GeV/c
Authors: AHMAD M. S. , KHAN M. Q. R. , HASAN R.
Published: November 2004

1635 fragments of charge two from 2550 12 C-Em interactions at 4.5 A GeV/c have been used to study the dependence of mean free path on the distance from the point of their emission. No evidence is found for the anomalously short mean free path in the first few centimeters of the point of emission.
DISC AND RP2 CORRECTIONS TO THE STRING EFFECTIVE LAGRANGIAN
Authors: CLINE JAMES M.
Published: November 2004

Bosonic string scattering amplitudes on the disc and the projective plane are compared with amplitudes from the effective field theory derived by demanding consistency of string propagation in background massless fields. Path integral (as opposed to BRST) quantization is used throughout, with the ghost fields integrated out. We point out a difficulty in defining a covariant dilaton vertex operator in this formalism. A nonstandard graviton vertex operator is constructed, by which we compute the vacuum energy for the two topologies and find that it has the correct ratio to the dilaton tadpole, as predicted by the effective Lagrangian. Factorization of tadpole divergences in N-point amplitudes leads to the same result, modulo a paradox discovered by Fischler, Klebanov, and Susskind, which is reviewed. We also show that the dilaton two- and three-point functions agree with the exponential form of the dilaton potential in the effective action, despite quadratic divergences that initially appear in these amplitudes.
BARYON NUMBER NONCONSERVATION IN A HIGH-DENSE POST-INFLATIONARY UNIVERSE
Authors: FERRER E. J. , DE LA INCERA V.
Published: November 2004

We found the temperature at which the electroweak baryon-number nonconserving processes are frozen, as a function of the fermion number density of the universe, which results in the increase of the freezing temperature with the growth of the fermion number density combination [Formula: see text]. We combine this result with the Affleck-Dine baryogenesis mechanism to suggest a possible scenario for the evolution of the post-inflationary universe, according to which the universe could have passed through a hot stage with large baryon and lepton asymmetries [Formula: see text], that are later erased at relatively low temperatures, the correct observational baryon asymmetry nB/nγ ~ 10−9 being finally produced.
ELECTRONIC STATES OF QUASIPERIODIC SYSTEMS: FIBONACCI AND PENROSE LATTICES
Authors: KOHMOTO MAHITO
Published: November 2004

Since the experiment of Shechtman et al. which suggests the crystal with the pentagonal symmetry (quasicrystal), there has been a lot of interest in the quasiperiodic systems. These can be regarded as being intermediate between ordered and disordered systems, and novel physical properties are expected. In fact, the quasicrystal in one-dimension is known to have exotic electronic properties: Cantor set energy spectrum, existence of self-similar and fractal wavefunctions and so on. These properties have intrinsically related to the renormalization-group theory and the nonlinear dynamical systems which could lead to chaos. The electronic properties of the Fibonacci lattice (1-D quasicrystal) and the Penrose lattice (2-D quasicrystal) are discussed.
THE AUGMENTED MODELS OF ASSOCIATIVE MEMORY ASYMMETRIC INTERACTION AND HIERARCHY OF PATTERNS
Authors: FEIGELMAN M.V. , IOFFE L.B.
Published: November 2004

The asymmetric modification of the Hopfield model of the associative memory is considered. It is shown that the asymmetry does not change the main properties of the model, but leads to the internal nonthermal noise. The modification of the Hopfield algorithm is proposed which can be used for storing the correlated patterns and its storage capacity is estimated. The hierarchical memory model is proposed and studied.
THE Q-COLOR PROBLEM ON A LATTICE
Authors: MATTIS DANIEL C.
Published: November 2004

We study a transfer matrix for the q-color problem in d dimensions (basically that of the T→0 limit of the q-state Potts antiferromagnet in d dimensions.) Its largest eigenvalue W=wN counts the number of distinct maps such that no two neighbors have the same color. This is relevant to a number of physical problems (ice, glassy materials, Potts antiferromagnet, etc.) in which the residual entropy (at T=0) plays an important role in determining the existence or absence of an order/disorder phase transition at a finite T. Our estimate of w for an hypercubic lattice (linear, square, simple cubic, etc.) is w≥1+[(q−2)d/(q−1)d−1].
EXAFS STUDY OF ICOSAHEDRAL Al Cr
Authors: SADOC A. , LAGARDE P. , SAINFORT P.
Published: November 2004

An EXAFS study above the Cr edge is reported for the icosahedral phase of an Al 86 Cr 14 alloy. Analysis of the EXAFS is made using different subshells of Al atoms to modelize the 1st neighbor shell around a Cr atom. An icosahedral model is tentatively presented with reference to the α-Al Mn Si structure.
NON-PERIODIC TRANSLATIONAL ORDER IN QUASICRYSTALS WITH STABLE ATOMIC DENSITY ON SEVERAL CELLS
Authors: KRAMER PETER
Published: November 2004

The projection of the cubic lattice in IE 3 to an intersecting plane IE 2 serves as a paradigm for non-periodic translational order. The quasicrystal model proposed has stable atomic density supported on three parallelogram cells. The Fourier transform is reduced to integrals over the three cells. In case of a periodic projection, the model reduces to the periodic crystal model in the plane with a single cell.
STRUCTURE AND PROPERTIES OF YBa2CU3O7−y IN THE NORMAL AND SUPERCONDUCTING STATE
Authors: Vasilev P. , Kostadinov I.Z. , Mateev M. , Gladkov P. , Mikhov M. , Nikolov J. , Kalkandjiev T.K. , Sevov S.
Published: November 2004

Here we present some new results on the srtucture and properties of the High Temperature Superconductor YBa 2 Cu 3 O 7−y synthesed at different technological conditions.
Y-Ba-Cu-O SUPERCONDUCTING CERAMICS
Authors: Tian Shunbao , Li Xiaofei , Wen Tinglian , Lin Zuxiang , Li Shichun , Yu Huijun
Published: November 2004

Polycrystalline Y-Ba-Cu-O superconducting materials have been studied. It was found that chemical composition and processing condition may play an important role in the final structure and superconducting properties.

The density has been determined and compared with the calculated value according to the structure model reported by Bell labs. The grain size and the morphology of the materials were observed by SEM.
HIGH-Tc SUPERCONDUCTIVITY AND STRUCTURE OF Y-Ba-Cu OXIDES REPLACED PARTIALLY BY La AND Li
Authors: Xu Yuhuan , Li Zhongrong , Li Chaorui , Wang Hong , Li Wu , Lin Xianduan
Published: November 2004

The compounds with the composition Ba(Y1−xLax)(Cu1−yLiy)2On have been prepared in ceramic form. It has been discovered that this ceramic (x=0.33, y=0.10) exhibits high- Tc superconductivity with Tc (middle point) of 90K and T R=zero of 82K. By SEM analysis, it was shown that the main phase is some rectangle grains with size of 2−10μm. From X-ray powder diffraction, the structure of main phase, which belongs to orthorhombic crystal class with the lattice parameters of a=3.895Å, b=3.888Å, and c=11.598Å at room temperature, was determinated.
EXPERIMENTAL STUDY ON THE MAGNETIC PENETRATION INTO Y-Ba-Cu-O SUPERCONDUCTORS
Authors: YAN Shousheng , JIA Qiuping , WANG Xu , XIA Guoqiang , MA Hong
Published: November 2004

Recently there have been several reports on the behaviour of granular superconductivity in high-Tc Y-Ba-Cu-O system. In granular superconductors, superconducting grains are weakly coupled to one another by the proximity Josephson effects. When an external field is applied, screening currents will develop in a region of the order of the effective penetration depth, which might be much greater than London penetration depth[1]. Using the Schawlow low-frequency method, the temperature, field and time dependences of the penetration depth in Y-Ba-Cu-O superconductors were studied. In this paper we present our results. which show the oxides have many of the features expected for a granular superconductor.
ELECTRON TUNNELING MEASUREMENTS OF ENERGY GAP IN SUPERCONDUCTORS YBaCuO, LaSrCuO AND BPBO
Authors: TAO Hongjie , CHEN Yingfei , LU Li , YANG Qiansheng , ZHAO Bairu , SHI Yinghuan , LU Yong , WANG Huisheng , ZHAO Yuying , LI Lin , FANG Yue , LIU Jinxiang , CHEN Liquan , TANG Disheng , WU Qianzhang
Published: November 2004

We have carried out superconducting energy gap measurements for polycrystalline perovskite-structure superconductors YBaCuO, LaSrCuO and BPBO with point contact tunneling. The tunneling conductance curves for YBaCuO, LaSrCuO and BPBO show the energy gap to transition temperature ratio 2Δ/kTc =4.7, 7.8 and 5.05 respectively, which is consistant with the strong-coupling superconductivity.
A CLUSTER STUDY OF MECHANISM IN THE NEW SUPERCONDUCTORS YBa2Cu3O7
Authors: Zeng Zhi , Zheng Qing-qi , Han Rushan
Published: November 2004

The electronic interaction between the copper ion and it’s environmental ions in the new high Tc superconductor (YBa2Cu3O7) is studied by the selfconsistent local density theory. The embedded cluster models with different kinds of copper ions and it’s oxygen neighbour are considered in this work. The Cu-O5 pyramid is responsible for the 2D conductor and the Cu-O4 square plane exhibits the semiconductor due to the instability. The modified exciton model[1] may respond to the high Tc superconductivity mechanism.
ELECTRONIC STRUCTURE AND SUPERCONDUCTING MECHANISM IN La2−yXyCuO4
Authors: Zhang Chunbin , Li Shaomeng , Teng Yagang , Zhang Wanxiang , Zhang Xinwei , Chen Shigang
Published: November 2004

Using LMTO method, the electronic structure of body centered tetragonal La2CuO4 is calculated. We discussed mechanism of superconductivity in the compounds with the energy band structure and shown that exciton mechanism of superconductivity could not play an essential role in raising the Tc.
Percolated Superconductivity and Electron-Electron Exchange Mechanism in Ba-La-Cu-O
Authors: Tao Ruibao
Published: November 2004

It is found that the oxygen vacancies at the Cu-O basal plane of oxide (La1−xBax)2CuO4−y (Balacuo) will break the bonds of Cu-O-Cu to make the hopping between those coppers disappear so that the electrical conduction in the Cu-O basal plane would become a bond percolation system consisting of an infinite cluster carrying the current with a great number of finite clusters hanging around. It is favorable to create some mechanism of electron-electron exchange so that the transition temperature Tc of superconductivity could be increased significantly. The comparison with Y1Ba2Cu3O9−y is also discussed briefly.
OXIDE SUPERCONDUCTIVITY RESEARCH AT NORTHWESTERN UNIVERSITY
Authors: KETTERSON J.B.
Published: November 2004

A short review was presented of a wide range of activities involving the high Tc oxide superconductors at the Northwestern University. Calculations of the charge density associated with the d9 shell of the copper atom in the Cu-O planes and the d8 shell of the copper atoms along the Cu-O lines of the unit cell of YBa2Cu3O7 performed by Freeman, Massida and Yu were presented. Results of a detailed study of the pseudoternery phase diagram involving CuO, BaO and YO1.5 were shown which verify the existence of three compounds having the Y:Ba:Cu ratios 123 (the high Tc superconductor), 211 (the so-called green phase) and 132 (a new insulating compound). This work, performed by Mason and coworkers, involved X-ray diffraction, optical spectroscopy, magnetic susceptibility, and electrical transport studies. Transport measurements by Poeppelmeier, Song, Hwu and coworkers on the assembledges YBaSrCu3O7 anf YBa2Cu3O5F2 were reported; no evidence of superconducting behavior at temperatures above 90K was seen in the latter. A detailed study of the magnetic and transport properties of the YBa2−xLaxCu3−xNixO7±δ system was reported. For small Ni concentration (x<0.3) a continuous drop in Tc was observed. For x= 0.4 and 0.5 evidence of two separate transitions, near 75K and 25K, were seen in the resistance (with the resistance going to zero at about 15K); for x=0.7 semiconducting behavior was observed. A continuous drop in the normalized diamagnetic signal was seen with increasing x with the diamagnetic fraction being below 5 % for x=0.7 and above. X-ray diffraction showed a continuous decrease in the orthorhombic fraction and an increase in the tetragonal fraction with increasing x. Results on d.c. magnetron sputtering of thin films on MgO from a stoichiometric 123 target in an argon atmosphere were shown. With proper annealing films with onset temperature of 90K and zero resistance at 68K have been prepared; this work was done by Jin, Lee, Song and coworkers. A brief report on the effect of O-stoichiometry on EPR and susceptibility measurements in the 123 compound performed by Hoffman and coworkers and NMR in the La2−xSrxCuO4 compound by Halpern and coworkers was presented.
MAGNETISM, FLUX QUANTISATION AND RF-SQUID MAGNETOMETRY IN HIGH-Tc CERAMIC SUPERCONDUCTORS
Authors: Gough C.E.
Published: November 2004

Measurements of magnetisation, flux quantisation and rf-SQUID operation using sintered high-Tc YBCO samples are presented and are described in terms of granular superconductor model with the strongly superconducting grains weakly connected at grain boundaries.
ELECTRONIC STRUCTURE AND ELECTRON-PHONON INTERACTION FOR La2-xMxCuO4 SYSTEMS
Authors: Aligia A.A. , Bennemann K.H. , Kulić M. , Zlatić V.
Published: November 2004

The electronic properties and the electron-phonon coupling in La2-xMxCuO4 type compounds are studied within the tight-binding theory. Derived expressions for electron-phonon coupling exhibit clearly the relative importance of various phonon modes. The possible role of the breathing type oxygen vibrations in the electronically driven lattice instabilities and superconductivity is discussed as a function of the impurity concentration.
A Model for Correlated Valence Fluctuation in High Tc Superconductors
Authors: Liang W.Y.
Published: November 2004

A simple model is proposed as a possible mechanism for high T c superconductivity in certain copper oxides based on correlated valence fluctuation. Electron pairs are formed by Coulomb attraction between electrons in mainly Cu2+ ( d 9 configuration) pyramidal planes mediated by Cu 3+ ( d 8 configuration) ions in the CuO 4 chain-like plane in YBa2Cu3O7−x . These electron pairs have high binding energies necessary for high Tc , and the model is capable of explaining a number of other observed properties.
WHICH ARE THE FUNDAMENTAL MAGNETIC FIELD CONFIGURATIONS IN NATURE?
Authors: SALINGAROS N.A.
Published: November 2004

The dipole field represents a magnetic paradigm. It occurs in a hierarchy of scale, from elementary particles, to ferromagnetic domains, to laboratory magnets, up to the earth itself. Nevertheless, the present magnetic paradigm for plasma physics and astrophysics is not the dipole, but the Beltrami field [Formula: see text], k a constant or scalar function. Such fields are regarded as the most stable, and are extensively used in models of cosmic and laboratory plasmas. The problem is that these two classes of supposedly paradigmatic vector fields are incompatible, as it is impossible to transform one into the other via a continuous limiting process. This paper attempts to resolve this basic contradiction by identifying the configurations corresponding to extrema of the field energy. It is found that, contrary to a long-held belief, Beltrami fields correspond to a point on an energy plane (the flat limiting case of a saddle) and not to a minimum. The classes of energy minima derived here include axisymmetric toroidal and axisymmetric poloidal fields. The latter naturally reduce to dipole fields in the limit of a microscopic current, in agreement with the magnetic paradigm. Some of the situations which have traditionally used Beltrami fields as a model can be explained with the minimum-energy fields derived here. The observed instability of axisymmetric magnetoplasmas follows from a separate energy equipartitioning mechanism.
MEAN FIELD APPROACH TO THE GAP OF A MODEL INTERACTING SYSTEM
Authors: BANERJEE KAJOLI , SINGH VIJAY A. , BHAT G. R.
Published: November 2004

The well-known local density approximation severely underestimates the gap of insulating materials. We undertake a study of an infinite one-dimensional model interacting system where the gap is known exactly. We use variational procedures, similar in spirit to Hohenberg and Kohn's derivation of the density functional theory. The mean field approximations so obtained are used to calculate the gap in the eigenspectrum. The gap is found to be systematically underestimated for realistic values of the parameters (u/t ≤ 4 where u is the Coulomb term and t, the transfer term). For u/t > 4, the approximate gap is in close agreement with the exact gap. The underestimation of the gap is investigated with respect to the discontinuity in the effective potential.
NON PERTURBATIVE TREATMENT OF ATTRACTIVE INTERACTIONS IN THE METALLIC LIMIT OF Cu - O HUBBARD HAMILTONIAN
Authors: Medina R. , Di Stasio M. , Geertsma W. , Marini-Bettolo U. , Pietronero L. , Sciutto S. J.
Published: November 2004

We study, by non perturbative methods, the nature of the attractive interaction via oxygen superexchange in the Cu - O Hubbard-type Hamiltonian. The approach is based on a comparison with an effective Hamiltonian and shows that the attractive interaction can be large and eventually overcome the effective repulsion in the metallic phase.
TWO-DIMENSIONAL ANTIFERROMAGNETIC HEISENBERG MODEL: EXACT AND RVB STATES
Authors: Poilblanc D.
Published: November 2004

The exact many-body states of a 10-site square cluster with periodic boundary conditions of a S = 1/2 antiferromagnetic Heisenberg lattice model are investigated. A general form of a Resonating Valence Bond wavefunction (RVB), written in fermion representation is examined. It is shown that the optimum variational wavefunction has complex singlet bond distribution amplitudes of s+id symmetry . It has a very large overlap with the groundstate, belongs to the same space group representation and its energy functional has a minimum very close to the ground-state energy. On the other hand, if the amplitudes are restricted to real numbers, the local minimum has slightly higher energy and d-wave symmetry.
ELASTIC STRAINS AND ENHANCED CRITICAL TEMPERATURE IN COPPER OXIDE SUPERCONDUCTORS
Authors: Guinea Francisco
Published: November 2004

The strong dependence of the critical temperature on the lattice parameters, and the existence of short coherence lengths in copper oxide superconductors make possible the appearance of regions with enhanced values of Tc near lattice distortions. Simple estimates show that this enhancement can be comparable to Tc itself near dislocations and other defects.
SUPERCONDUCTING AND MINOR PHASES IN Bi-Sr-Ca-Cu-O SYSTEM
Authors: Sasvári J. , Pekker S. , Csordás Tóth A. , Hutiray Gy. , Mihály L.
Published: November 2004

Ceramics of various nominal composition in the Bi-Sr-Ca-Cu-O system were studied by X-ray powder diffraction and electron beam microanalysis. Electrical resistivity measurements were also carried out.

Efforts were made to prepare various phase compositions in the Bi-Sr-Ca-Cu-O system, such as the Bi 2 Sr 2 Ca 2 Cu 3 O 10 (from now on we use the commonly accepted composition denotion by cation stoichiometry, here 2223), 2212 and 2201, with T c = 110 K , 70 K and 20 K, respectively. Experiments included higher calcium ratio samples such as the 4334 and related compositions. All studied samples contained minor phases besides the main ones. However, their amount of minor phases was below the detectability limit (~3 %) of the X-ray diffractometry. Presence of CuO was shown by electron beam microanalysis. Ca 2 CuO 3, Sr y Ca 2−y CuO 3 ( y ≤ 0.2) and Bi-rich phases were very often detected.

In this paper, X-ray patterns of the phases with caracteristic composition are given together with the results of electrical resistivity measurements.
Macroscopic Magnetic Properties of High Temperature Superconductors: Effect of a Pinning Barrier Distribution
Authors: Malozemoff A. P. , Worthington T. K. , Yandrofski R. M. , Yeshurun Y.
Published: November 2004

The magnetic properties of YBaCuO crystals are strongly affected by thermally activated flux creep over pinning barriers. Here the effect of a power-law distribution of pinning barriers is explored. The critical current density is predicted to have a power-law dependence on the reduced temperature difference approaching the transition temperature T c and a logarithmic dependence on the timescale of the measurement. The dependence of the critical current on the measurement time provides a possible explanation of the disparity between the critical current measured in thin film transport experiments and J c obtained from magnetic data. Also, in contrast to some earlier theory, the normalized logarithmic time derivative of the remanent magnetization is shown to not diverge near T c , irrespective of the pinning barrier distribution.
EFFECT OF THE EQUILIBRATING TEMPERATURE ON THE CRITICAL TEMPERATURE OF CERAMIC YBa2Cu3Oy
Authors: Oszlányi G. , Pekker S. , Hutiray Gy. , Zsoldos E. , Mihály L.
Published: November 2004

The transition temperature of YBa 2 Cu 3 O y ceramic samples were studied as a function of oxygen content by DC electrical resistivity measurements. Two series of samples had been prepared by equilibrating pieces from the fully oxidized orthorombic and fully reduced tetragonal phase at "low" (series I 420 °C) and "high" (series II 600 °c) temperatures. The T c vs. oxygen content dependence was found to show a continuous change in series II and a 55 K plateau around y = 6.6–6.7 in series I. A current dependence was observed in series I in the range y = 6.5–6.6 where room temperature X-ray data may indicate the occurence of more than one orthorombic phases.
PHASE TRANSITION IN TWO-DIMENSIONAL DILUTE ISING COULOMB GAS
Authors: SZETO K. Y.
Published: November 2004

The magnetic phase diagram of a dilute gas carrying an Ising spin variable and an electronic charge in two dimensions is investigated using a self consistent screening analysis. The bare interaction consists of a long range logarithmic potential which can be attractive (repulsive) for antiparallel (parallel) Ising spins and a screened Coulomb repulsion. The Ising Coulomb gas exhibits a real space pairing of antiparallel spins at low temperature and a plasma phase of free particles at high temperatures. The relevance of this model to pair formation in high temperature superconductors is discussed in the context of doped La 2 CuO 4.
SERIES ANALYSIS OF Q-STATE CHECKERBOARD POTTS MODELS
Authors: HANSEL D. , MAILLARD J. M.
Published: November 2004

The series analysis of the low temperature expansion of the checkerboard q-state Potts model in a magnetic field initiated in two previous papers is continued. In particular algebraic varieties of the parameter space (corresponding or generalizing the so-called disorder solutions), the checkerboard Potts model and its Bethe approximation are indistinguishable as far as one is concerned with the partition function and its first order derivatives. The difference between the two models occurs for higher order derivatives. In particular one gives the exact expression of the (low temperature expansion of the) susceptibility of the checkerboard Ising model in zero magnetic field on one of these varieties.
NQR AND NMR STUDIES OF YBa2Cu3Ox(6.0 ≦ x ≦ 6.91)
Authors: IMAI TAKASHI , SHIMIZU TADASHI , YASUOKA HIROSHI , UEDA YUTAKA , KOSUGE KOJI
Published: November 2004

Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) have been utilized to investigate the 90 K class superconductor YBa 2 Cu 3 O 6.91 and relevant oxides YBa 2 Cu 3 O x(6.0 ≦ x ≦ 6.91). Two 63 Cu NQR lines have been observed at about 31 MHz and 22 MHz for x = 6.91, which were proved to be from the Cu2 and Cu1 sites respectively using the NMR technique for an oriented sample. The spin-lattice relaxation time T1 exhibits anomalous temperature dependence with high relaxation rate in the normal state. Power-law like temperature dependence was observed well below T c for the Cu2 sites. The former indicates the strong influence of Cu spin fluctuations, while the latter may be understood as the realization of the anisotropic superconductivity. Antiferromagnetic nuclear resonance has been obtained for x = 6.0 yielding a clear evidence of magnetic ordering in the Cu2-O 2 planes. This is consistent with neutron scattering and μ SR studies.
VAN DER WAALS CONTRIBUTION TO THE THERMODYNAMICAL PROPERTIES OF THE CURVILINEAR SURFACES
Authors: NABUTOVSKII V. M. , BELOSLUDOV V. R.
Published: November 2004

This article is a review of our papers devoted to the application of the Lifshitz, Dzjaloshinskii, Pitaevskii theory for the theoretical investigation of the thermodynamical properties of the plane, spherical and cylindrical interfaces and layers. In accordance with this theory the thermodynamical properties of the surface are determined by the fluctuating electromagnetic field. This field may be characterized by the averaged quadratic combinations of the electric and magnetic strength which are thermodynamical Green functions of this field. We have obtained these Green functions for the spherical and cylindrical interfaces and applied them for the calculations of the different thermodynamical quantities such as electromagnetic stress tensor, chemical potential, and density variation. We have shown that, in general, it is not valid to obtain size and form dependence of the thermodynamical quantities by using two-particle Van der Waals potential. We discuss the surface tension dependence of the particle (or hole) and homogeneous and heterogeneous nucleation.
THEORY OF BOUND MAGNETIC POLARONS IN DILUTED MAGNETIC SEMICONDUCTORS
Authors: THIBBLIN U.
Published: November 2004

The present status of the theory of bound magnetic polarons in diluted magnetic semiconductors is reviewed. Optical experiments on bound magnetic polarons and a comparison between theory and experiments are discussed.
SUPERCONDUCTING PROPERTIES OF THE HIGH Tc SUPERCONDUCTING Er-Ba-Cu-O COMPOUND
Authors: NAQVI S. M. M. R. , AHMAD FIROZ , ALAM JAWAID , AHMAD SHARFUDDIN
Published: November 2004

Two batches of Er-Ba-Cu-O superconductors have been prepared. The zero resistance temperature is 86 K with T c onsets at 99 K and 92 K respectively. Susceptibility measurements show superconducting phase at LN 2. X-ray diffraction results indicates two phases, the superconducting being the major one.
A NEUTRON DIFFRACTION STUDY OF A SUPERCONDUCTING CUPRATE OF THE Bi–Ca–Sr–Cu–O SYSTEM CONTAINING TWO Cu-O SHEETS
Authors: SEQUEIRA A. , RAJAGOPAL H. , GANAPATHI L. , VIJAYARAGHAVAN R. , RAO C. N. R.
Published: November 2004

The structure of a nominally Ca-rich composition of the n = 2 member of the Bi 2 (Ca, Sr) n+1 Cu n O 2n+4 series has been investigated by neutron diffraction profile analysis. The results suggest that the Amaa space group may be more appropriate than the Fmmm space group.