July 1996 arXiv papers — page 11

Zouhair Tamsamani

This paper constitutes a recent work using the constructions of a previous preprint alg-geom/9512006 to show that the functors geometric realisation and Poincaré $n$-groupoid induce an equivalence between the category of $n$-grouppoids and the category of $n$-truncated topological spaces, when we localise both categories by weak equivalence.

Markus Finkemeier, Matt McIrvin

The heavy quark effective field theory Lagrangian is renormalized to order 1/m^2. Our technique eliminates operators that vanish by the equation of motion by continuously redefining the heavy quark fields during renormalization. It is consequently only necessary to calculate the running of the operators that do not vanish by the equation of motion. Our resul

Charles G. Hoopes, Rene A. M. Walterbos, Bruce E. Greenawalt

We present a study of the diffuse ionized gas (DIG) in three Sculptor group galaxies: NGC 55, NGC 253, and NGC 300. The study is based on narrow band imagery in H-alpha+[NII](6548+6583A) and [SII] (6717+6731A). We find that DIG contributes 33 to 58% of the total H-alpha luminosity in these galaxies, or 30 to 54% after correcting for scattered light. We find

Susanna Manrubia, Maya Paczuski

A mathematical model of interacting species filling ecological niches left by the extinction of others is introduced. Species organize themselves into genera of all sizes. The size of a genus on average grows linearly with its age, confirming a general relation between Age and Area proposed by Willis. The ecology exhibits punctuated equilibrium. Analytic and

Takesi Saito, Kunihiko Uehara

We apply the gauge theory on $M_4\times Z_2$ geometry previously proposed by Konisi and Saito to the Weinberg-Salam model for electroweak interactions, especially in order to clarify the geometrical meaning of curvatures in this geometry. Considering the Higgs field to be a gauge field along $Z_2$ direction, we also discuss the BRST invariant gauge fixing in

Nathan Berkovits

The free action for massless Ramond-Ramond fields is derived from closed superstring field theory using the techniques of Siegel and Zwiebach. For the uncompactified Type IIB superstring, this gives a manifestly Lorentz-covariant action for a self-dual five-form field strength. Upon compactification to four dimensions, the action depends on a U(1) field stre

C. Dong, H. Li, G. Mason, S. P. Norton

It is shown how certain idempotents in the Griess algebra generate the discrete series representations for the Virasoro algebra inside the Frenkel-Lepowsky-Meurman's moonshine module vertex operator algebra. It is also shown that each Niemeier lattice determines (in many ways) certain maximal associative subalgebras of the Griess algebra.

M. Irac-Astaud

Two differential calculi are developped on an algebra generalizing the usual q-oscillator algebra and involving three generators and three parameters. They are shown to be invariant under the same quantum group that is extended to a ten-generator Hopf algebra. We discuss the special case where it reduces to a deformation of the invariance group of the Weyl-H

Atsuo Kuniba, Kailash C. Misra, Masato Okado, Jun Uchiyama

We give a criterion for the Demazure crystal $B_w(λ)$ defined by Kashiwara to have a tensor product structure. We study the $\sln$ symmetric tensor case, and see some Demazure characters are expressed using Kostka-Foulkes polynomials.

H. T. Koelink, J. Van der Jeugt

The interpretation of the Meixner-Pollaczek, Meixner and Laguerre polynomials as overlap coefficients in the positive discrete series representations of the Lie algebra su(1,1) and the Clebsch-Gordan decomposition leads to generalisations of the convolution identities for these polynomials. Using the Racah coefficients convolution identities for continuous H

Alfred Stadler, Franz Gross

First results for the triton binding energy obtained from the relativistic spectator or Gross equation are reported. The Dirac structure of the nucleons is taken into account. Numerical results are presented for a family of realistic OBE models with off-shell scalar couplings. It is shown that these off-shell couplings improve both the fits to the two-body d

L. Phair, Th. Rubehn, L. G. Moretto, G. J. Wozniak

Mastinu et al. recently reported the observation of several positive signals possibly indicating critical behavior in peripheral collisions of Au+Au at $E/A$=35 MeV. In our comment, we examine the choice of variables used to determine the presence (or absence) of critical behavior. We do this by repeating the analysis the work of Mastinu et al. on "data&

L. G. Moretto, Th. Rubehn, L. Phair, N. Colonna

A new, sensitive method allows one to search for the enhancement of events with nearly equal-sized fragments as predicted by theoretical calculations based on volume or surface instabilities. Simulations have been performed to investigate the sensitivity of the procedure. Experimentally, charge correlations of intermediate mass fragments emitted from heavy i

Th. Rubehn, K. X. Jing, L. G. Moretto, L. Phair

Fission excitation functions of compound nuclei in a mass region where shell effects are expected to be very strong are shown to scale exactly according to the transition state prediction once these shell effects are accounted for. The fact that no deviations from the transition state method have been observed within the experimentally investigated excitatio

Douglas W. McKay, Herman J. Munczek

We solve the Dyson--Schwinger equation for the quark propagator in a model with singular infrared behavior for the gluon propagator. We require that the solutions, easily found in configuration space, be tempered distributions and thus have Fourier transforms. This severely limits the boundary conditions that the solutions may satisify. The sign of the dimen

Carl M. Bender, Luis M. A. Bettencourt

Conventional weak-coupling Rayleigh-Schrödinger perturbation theory suffers from problems that arise from resonant coupling of successive orders in the perturbation series. Multiple-scale analysis, a powerful and sophisticated perturbative method that quantitatively analyzes characteristic physical behaviors occurring on various length or time scales, avoids

W. A. Rodrigues, Q. A. G. de Souza, J. Vaz, P. Lounesto

In this paper we study Dirac-Hestenes spinor fields (DHSF) on a four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields must be defined as certain equivalence classes of even sections of the Clifford bundle (over the RCST), thereby being certain particular sections of a new bundle named Spin-Clifford bundle (SCB). The conditions for the

Gabriele Ferretti

We study the large N limit of the MATRIX valued Gross-Neveu model in 2<d<4 dimensions. The method employed is a combination of the approximate recursion formula of Polyakov and Wilson with the solution to the zero dimensional large N counting problem of Makeenko and Zarembo. The model is found to have a phase transition at a finite value for the critical tem

Pietro Menotti, Pier Paolo Peirano

We consider families of geometries of D--dimensional space, described by a finite number of parameters. Starting from the De Witt metric we extract a unique integration measure which turns out to be a geometric invariant, i.e. independent of the gauge fixed metric used for describing the geometries. The measure is also invariant in form under an arbitrary ch

Debajyoti Choudhury, Maria Krawczyk

A light neutral Higgs boson in the framework of the general two Higgs doublet model (2HDM) is not excluded by existing data. We point out that it can be looked for at the proposed low energy $γγ$ collider. Failure to detect one may lead to important limits on the parameters of the general 2HDM.

H. M. Fried, Y. Gabellini

A functional formulation and partial solution is given of the non-abelian eikonal problem associated with the exchange of non-interacting, charged or colored bosons between a pair of fermions, in the large $s$/small $t$ limit. A simple, functional ``contiguity&#34; prescription is devised for extracting those terms which exponentiate, and appear to generate

Toby Falk

We combine experimental bounds on the electric dipole moments of the neutron and electron with cosmological limits on the relic density of a gaugino-type LSP neutralino to constrain certain CP-violating phases appearing in the MSSM. We find that in the Constrained MSSM, the phase |θ_μ| < π/10, while the phase θ_A remains essentially unconstrained.

Maria Krawczyk

Present data do not rule out the light neutral Higgs particle $h$ or $A$ in the framework of the general 2HDM. The discovery reach/exclusion limits of the Yukawa process $Z\rightarrow f {\bar f} h/A$, ($f= b$ quark or $τ$ lepton) at LEP I and of the gluon-gluon fusion at HERA is discussed. In addition the possible search for very light Higgs particle in $γγ$

Bernard Pire

The concept of color transparency is introduced. This new feature of QCD is characteristic of a gauge theory. It enables strong interactions to be studied in a new domain: scattering amplitudes of transversally small color singlet objects. Experimental data are still few and somehow inconclusive. Future prospects are briefly discussed. This is a frontier pro

M. Boglione, M. R. Pennington

It has been recently claimed that the Inverse Amplitude Method provides a reliable unitarisation of Chiral Perturbation Theory allowing resonance poles to be accurately uncovered. We illustrate the sensitivity of these claims to the treatment of the Adler zero and to assumptions about the left hand cut (and hence about the underlying exchange forces). Previo

A. Capella, A. Kaidalov, A. Kouider Akil, C. Gerschel

We study the combined effect of nuclear absorption and final state interaction with co-moving hadrons on the $J/Ψ$ and $Ψ&#39;$ suppression in proton-nucleus and nucleus-nucleus collisions. We show that reasonable description of the experimental data can be achieved with theoretically meaningful values of the cross-sections involved and without introducing a

David Fein, Zheng Huang, Peter Valerio, Ina Sarcevic

We calculate the dilepton emissions as the decay product of the charm and bottom quarks produced in heavy-ion collisions at RHIC energy. We take into account the next-to-leading-order radiative corrections in perturbative QCD to the heavy quark production from both an initial hard parton-parton scattering and an ideal quark-gluon plasma. We find that the the

P. Rehberg, S. P. Klevansky, J. Hüfner

The temperature dependence of the elastic scattering processes $qq&#39;\to qq&#39;$ and $q\bar q&#39;\to q\bar q&#39;$, with $q, q&#39; = u, d, s$ is studied as a function of the scattering angle and the center of mass energy of the collision within the framework of the $SU_f(3)$ Nambu--Jona--Lasinio model. Critical scattering at threshold is observed in the

J. Blümlein, N. Kochelev

The twist--2 contributions to the polarized structure functions in deep inelastic lepton--hadron scattering are calculated including the exchange of weak bosons and using both the operator product expansion and the covariant parton model. A new relation between two structure functions leading to a sequence of new sum rules is found. The light quark mass corr

Julian Borrill, Marcelo Gleiser

The study of nonlinear phenomena in systems with many degrees of freedom often relies on complex numerical simulations. In trying to model realistic situations, these systems may be coupled to an external environment which drives their dynamics. For nonlinear field theories coupled to thermal (or quantum) baths, discrete lattice formulations must be dealt wi

A. R. Levi, V. Lubicz, C. Rebbi

We discuss a general strategy to compute the coefficients of QCD chiral Lagrangian by using the lattice regularization of QCD with Wilson fermions. This procedure requires the introduction of an effective Lagrangian for lattice QCD as an intermediate step in the calculation. The continuum QCD chiral Lagrangian can be then obtained by expanding the lattice ef

S. V. Chekanov

Local multiplicity fluctuations of hadrons produced in the decay of $Z^0$ were studied on the basis of L3 data. In addition to the normalized-factorial-moment method, the fluctuations were studied for the first time by the use of bunching parameters. A strong multifractal structure was observed inside jets. JETSET 7.4 PS describes the fluctuations in the azi

G. &#39;t Hooft

If one assumes the validity of conventional quantum field theory in the vicinity of the horizon of a black hole, one does not find a quantum mechanical description of the entire black hole that even remotely resembles that of conventional forms of matter; in contrast with matter made out of ordinary particles one finds that, even if embedded in a finite volu

J. K. Freericks, V. Zlatic

The exact solution of the spin one-half Falicov-Kimball model, with random hopping between the lattice sites, is used to explain the anomalous magnetic response of Yb-based valence-fluctuating intermetallic compounds. The anomalous behavior arises from an entropy-driven local-moment--nonmagnetic transition of unhybridized Yb ions in these materials which can

V. V. Flambaum, G. F. Gribakin, F. M. Izrailev

It is shown that the two-body character of the interaction in a many-body system gives rise to specific correlations between the components of compound states, even if this interaction is completely random. Surprisingly, these correlations increase with the increase of the number of active (valence) particles. Statistical theory of transition amplitudes betw

S. F. Burlatsky, J. G. Berberian, J. Shore, W. P. Reinhardt

We present a simple mechanical model for dynamic wetting phenomena. Metallic balls spread along a periodically corrugated surface simulating molecules of liquid advancing along a solid substrate. A vertical stack of balls mimics a liquid droplet. Stochastic motion of the balls, driven by mechanical vibration of the corrugated surface, induces diffusional mot

N. Kumar

The quantum Hall conductance of a disordered two-dimensional gas of non-interacting electrons is re-examined for its integrity against disorder in the limit of no mixing between different Landau levels. The exact one-electron eigenstates of the disordered system are shown to be current carrying, with exactly the same Hall current as in the absence of disorde

Shiwei Zhang, J. Carlson, J. E. Gubernatis

We describe and discuss a recently proposed quantum Monte Carlo algorithm to compute the ground-state properties of various systems of interacting fermions. In this method, the ground state is projected from an initial wave function by a branching random walk in an over-complete basis of Slater determinants. By constraining the determinants according to a tr

Michael Dorna, Martin C. Emele

This article gives an overview of a new semantic-based transfer approach developed and applied within the Verbmobil Machine Translation project. We present the declarative transfer formalism and discuss its implementation.

Michael Dorna, Martin C. Emele

This article presents a new semantic-based transfer approach developed and applied within the Verbmobil Machine Translation project. We give an overview of the declarative transfer formalism together with its procedural realization. Our approach is discussed and compared with several other approaches from the MT literature.

M. Apostol

A Thomas-Fermi model of a spherical shell of positive charge is investigated, under various boundary conditions. The electron distribution and the ionization charge are given particular attention.

Carmelo Pisani

A study of the quantum triangular billiard requires consideration of a boundary value problem for the Green&#39;s function of the Laplacian on a trianglar domain. Our main result is a reformulation of this problem in terms of coupled non--singular integral equations. A non--singular formulation, via Fredholm&#39;s theory, guarantees uniqueness and provides a

M. Van der Klis, J. H. Swank, W. Zhang, K. Jahoda

We report the discovery, with NASA&#39;s Rossi X-ray Timing Explorer (RXTE), of the first sub-millisecond oscillation found in a celestial X-ray source. The quasi-periodic oscillations (QPO) come from Sco X-1 and have a frequency of approximately 1100 Hz, amplitudes of 0.6-1.2% (rms) and are relatively coherent, with Q up to ~10^2. The frequency of the QPO i

E. Vazquez-Semadeni, T. Passot, A. Pouquet

We investigate the properties of highly compressible turbulence, the compressibility arising from a small effective polytropic exponent $γ_e$ due to cooling. In the limit of small $γ_e$, the density jump at shocks is shown to be of the order of $e^{M^2}$. Without self-gravity, the density structures arising in the moderately compressible case consist mostly

O. Meincke

This report provides a description of unbunched beam stochastic cooling in the framework of control theory. The main interest in the investigation is concentrated on the beam stability in an active cooling system. A stochastic cooling system must be considered as a closed-loop, similar to the feedback systems used to damp collective instabilities. These syst

D. K. Klimov, D. Thirumalai

We point out that the correlation between folding times and $σ= (T_{θ} - T_{f})/T_{θ}$ in protein-like heteropolymer models where $T_{θ}$ and $T_{f}$ are the collapse and folding transition temperatures was already established in 1993 before the other presumed equivalent criterion (folding times correlating with $T_{f}$ alone) was suggested. We argue that th

L. Frankfurt, W. Koepf, J. Mutzbauer, G. Piller

We discuss the coherent leptoproduction of vector mesons from polarized deuterium as a tool to investigate the evolution of small size quark-gluon configurations. Kinematic regions are determined where the final state interaction of the initially produced quark-gluon wave packet contributes dominantly to the production cross section. Two methods for an inves

Bernd Krause

Higher-order hadronic contributions to the anomalous magnetic moment of the electron, muon, and $τ$ lepton are considered in detail. As a main result we find a reduction by $-11 \times 10^{-11}$ for the g-2 of the muon as compared to previous calculations. Analytical expressions for the kernel functions of higher-order hadronic effects are presented. We empl

Jenni Adams, Ulf H. Danielsson, Dario Grasso, Héctor Rubinstein

In this paper we study the effect of a magnetic field on the fluctuation spectrum of the cosmic microwave background. We find that upcoming measurements might give interesting bounds on large scale magnetic fields in the early Universe. If the effects are seen, it might be possible to establish the presence of different fields in different patches of the sky

D. A. Johnston

We review recent work in the lattice approach to random surfaces and quantum gravity. Our task is made somewhat easier by some very interesting results, particularly in four dimensions, that have appeared recently and which are reported elsewhere in these proceedings. Inevitably, given the scope of the review and the limitations of space, the presentation wi

O. Prus, A. Auerbach, Y. Aloni, U. Sivan

We investigate effects of short range interactions on the addition spectra of quantum dots using a disordered Hubbard model. A correlation function \cS(q) is defined on the inverse compressibility versus filling data, and computed numerically for small lattices. Two regimes of interaction strength are identified: the even/odd fluctuations regime typical of F

Debnarayan Jana

The physical and mathematical mechanism behind diamagnetism of N (finite) spinless bosons (relativistic or non-relativistic) is well known. The mathematical signature of this diamagnetism follows from Kato&#39;s inequality while its physical way of understanding goes back to Van Leewen. One can guess that it might be true in the field theoretic case also. Wh

Hai-Yang Cheng

The proton spin problem triggered by the EMC experiment and its present status are closely examined. Recent experimental and theoretical progresses and their implications are reviewed. It is pointed out that the sign of the sea-quark polarization generated perturbatively by hard gluons via the anomaly mechanism is predictable: It is negative if the gluon spi

Hsien-chung Kao, Shih-Chang Lee, Wen-Jer Tzeng

We solve exactly a class of Frenkel-Kontorova models with piecewise parabolic potential, which has $d$ sub-wells in a period. With careful analysis, we show that the phase diagram of the minimum enthalpy configurations exhibits the structure of a complete $d$-dimensional devil&#39;s staircase. The winding number of a minimum enthalpy configuration is locked

Ryszard Horodecki, Michal Horodecki

Information-theoretic aspects of quantum inseparability of mixed states are investigated in terms of the $α$-entropy inequalities and teleportation fidelity. Inseparability of mixed states is defined and a complete characterization of the inseparable $2\times2$ systems with maximally disordered subsystems is presented within the Hilbert-Schmidt space formali

A. Ballesteros, F. J. Herranz, C. M. Pereña

A non-linear map is applied onto the (non-standard) null-plane deformation of (3+1) Poincaré algebra giving rise to a simpler form of this triangular quantization. A universal $R$-matrix for the null plane quantum algebra is then obtained from a universal $T$-matrix corresponding to a Hopf subalgebra. Finally, the associated Poincaré Poisson--Lie group is qu

Joseph Donin, Dmitry Gurevich, Steven Shnider

In this paper we describe a multiparameter deformation of the function algebra of a semisimple coadjoint orbit. In the first section we use the representation of the Lie algebra on a generalized Verma module to quantize the Kirillov bracket on the family of semisimple coadjoint orbits of a given orbit type. In the second section we extend this construction t

A. F. Krutov, D. I. Muravyev, V. E. Troitsky

An effective algebraic approach to $S$--matrix factorization into Jost matrices is developed in the case of coupled channels. The Jost matrix is given as a solution of boundary value Riemann -- Hilbert problem. A rational form is assumed for tangent of mixing angle, while there is no limitations for approximation of phase shifts.

A. S. Rinat

It is shown that no set of reasonable assumptions leads to a structure function as a convolution of the PWIA and a FSI contribution.

J. Pochodzalla, ALADIN collaboration

More than two decades ago, the van der Waals behavior of the nucleon - nucleon force inspired the idea of a liquid-gas phase transition in nuclear matter. Heavy-ion reactions at relativistic energies offer the unique possibility for studying this phase transition in a finite, hadronic system. A general overview of this subject is given emphasizing the most r

G. Imme, ALADIN collaboration

We report on temperature measurements of nuclear systems formed in the Au+Au collisions at incident energies of 50, 100, 150, 200 and 1000 A MeV. The target spectator matter was studied at the highest energy and the interacting zone (participants) at the lower ones.The temperature deduced from the isotope ratios was compared with the one deduced via the exci

W. F. J. Mueller, ALADIN collaboration

Signatures of critical behaviour in nuclear fragmentation are often based on arguments from percolation theory. We demonstrate with general thermodynamic considerations and studies of the Ising model that the reliance on percolation as a reference model bears the risk of missing parts of the essential physics.

Frédéric Campana, Thomas Peternell

The purpose of this paper is to translate positivity properties of the tangent bundle (and the anti-canonical bundle) of an algebraic manifold into existence and movability properties of rational curves and to investigate the impact on the global geometry of the manifold $X$. Among the results we prove are these: \quad If $X$ is a projective manifold, and ${

Thomas Peternell

This paper, a continuation of ``Towards a Mori theory on compact Kähler manifolds, 1&#39;&#39; (written with F. Campana), introduces a non-algebraic analogue to Mori theory in dimension 3.

Frédéric Campana, Jean-Pierre Demailly, Thomas Peternell

We investigate compact complex manifolds of dimension three and second Betti number $b_2(X) = 0$. We are interested in the algebraic dimension $a(X)$, which is by definition the transcendence degree of the field of meromorphic functions over the field of complex numbers. The topological Euler characteristic $χ_{\mathrm{ top}}(X) $ equals the third Chern clas

Ryszard A. Komorowski, Nicole Tomczak-Jaegermann

This note contains a corrected proof of the main result (which remains unchanged) from [K-T]. It was recently observed that an argument in a basic technical criterium has a gap.

Elso Drigo Filho, Regina Maria Ricotta

The usual concept of shape invariance is discussed and one extension of this concept is suggested.

John H. Schwarz

Recent developments in superstring theory have led to major advances in understanding. After reviewing where things stood earlier, we sketch the impact of recently identified dualities and D-branes, as well as a hidden eleventh dimension.

N. Dorey, V. V. Khoze, M. P. Mattis

The exact solution of N=2 supersymmetric QCD found by Seiberg and Witten includes a prediction for all multi-instanton contributions to the low-energy dynamics. In the case where the matter hypermultiplets are massless, the leading non-perturbative contribution at weak coupling comes from the two-instanton sector. We calculate this contribution from first pr

N. Banerjee, R. Banerjee, S. Ghosh

We develop a method based on the generalised Stückelberg prescription for discussing bosonisation in the low energy regime of the SU(2) massive Thirring model in 2+1 dimensions. For arbitrary values of the coupling parameter the bosonised theory is found to be a nonabelian gauge theory whose physical sector is explicitly obtained. In the case of vanishing co

P. Bouwknegt, K. Schoutens

We present a `spinon formulation&#39; of the $SU(n)_1$ Wess-Zumino-Witten models. Central to this approach are a set of massless quasi-particles, called `spinons&#39;, which transform in the representation ${\bf \bar{n}}$ of $su(n)$ and carry fractional statistics of angle $θ= π/n$. Multi-spinon states are grouped into irreducible representations of the yang

N. G. Stefanis

The infrared regime of fermionic Green and vertex functions is studied analytically within a geometric approach which simulates soft interactions by an {\it effective} theory of contours. Expanding the particle path integral in terms of dominant contours at large distances, all-order results in the coupling constant are obtained for the renormalized fermion

E. Benedict, R. Jackiw, H. -J. Lee

We discuss the quantization of pure string--inspired dilaton--gravity in $(1+1)$--dimensions, and of the same theory coupled to scalar matter. We perform the quantization using the functional Schroedinger and BRST formalisms. We find, both for pure gravity and the matter--coupled theory, that the two quantization procedures give inequivalent ``physical&#39;&

C. Mukku

Configuration space heat-kernel methods are used to evaluate the determinant and hence the effective action for an SU(2) doublet of fermions in interaction with a {\it covariantly constant} SU(2) background field. Exact results are exhibited which are applicable to {\it any} Abelian background on which the only restriction is that $(B^{2}-E^{2})$ and $E\cdot

P. S. Howe, P. C. West

The operator product expansion in four-dimensional superconformal field theory is discussed. The OPE takes a particularly simple form for chiral operators, in $N=1$ and $N=2$, and for analytic operators, in $N=2$ and $N=4$. It is argued that the Green&#39;s functions of such operators can be determined up to constants.

F. Benatti, R. Floreanini

Models that provide experimentally testable violations of ordinary Quantum Mechanics have been recently proposed. These models are based on non-unitary time evolutions of density matrices that are generated by linear positive maps. We discuss the consequences of imposing a stronger condition on those maps, known as complete positivity. It turns out that expe

I. Antoniadis, B. Pioline

Low--energy limits of N=2 supersymmetric field theories in the Higgs branch are described in terms of a non--linear 4--dimensional sigma--model on a \hk target space, classically obtained as a \hk quotient of the original flat hypermultiplet space by the gauge group. We review in a pedagogical way this construction, and illustrate it in various examples, wit

A. Chamseddine, H. Dreiner

We extend the Standard Model gauge group by a a gauged $U(1)_R$ R-Symmetry or a gauged $U(1)&#39;$. The requirement of cancellation of anomalies is very constraining but can be achieved by adding three or four hidden-sector fields which are Standrad Model singlets. The $U(1)_R$ or $U(1)&#39;$ quantum numbers of these singlets are usually large producing a no

D. S. Henty, C. Parrinello, D. G. Richards, J. I. Skullerud

We investigate the phenomenology of the Landshoff-Nachtmann two-gluon-exchange model of the Pomeron using gluon propagators computed in the Landau gauge within quenched lattice QCD simulations. As the propagators have been evaluated entirely from QCD first principles, our results provide a consistency check of the model. Finally, we report a proposal to inve

B. Ziaja

The multiparton density matrices of the QCD gluon cascade are investigated. The generating functional and master equation for momentum space multiparton density in the double logarithmic approximation (DLA) are proposed.

Hsiang-nan Li

We propose a unified and simple viewpoint to various evolution equations appropriate in different kinematic regions. We show that the resummation technique reduces to the Altarelli-Parisi equation, if the transverse degrees of freedom of a parton are ignored, to the Balitskii-Fadin-Kuraev-Lipatov equation, if the momentum fraction of a parton vanishes, and t

B. A. Kniehl

These lecture notes give a pedagogical introduction to the use of dispersion relations in loop calculations. We first derive dispersion relations which allow us to recover the real part of a physical amplitude from the knowledge of its absorptive part along the branch cut. In perturbative calculations, the latter may be constructed by means of Cutkosky&#39;s

Walter Wilcox

Direct evaluation of charged particle polarizabilities on the lattice is quite difficult. However, a short cut for charged pion polarizability - the Das, Mathur, Okubo Sum Rule - can readily be calculated using lattice techniques. A phenomenological model has been developed to fit the time behavior of the propagators in this expression. Numerical systematics

Mika Karjalainen, Janne Peisa

We apply dimensional reduction to the finite temperature U(1)+Higgs theory and study the properties of the reduced 3-dimensional theory in the broken phase using lattice Monte Carlo simulations. We compute analytically the scalar condensate in optimized 2-loop perturbation theory and the correlators in 1-loop perturbation theory. These quantities are also ca

A. R. Levi, V. Lubicz, C. Rebbi

We discuss a general strategy to compute the coefficients of the QCD chiral Lagrangian using lattice QCD with Wilson fermions. This procedure requires the introduction of a lattice chiral Lagrangian as an intermediate step in the calculation. The QCD chiral Lagrangian is then obtained by expanding the lattice effective theory in increasing powers of the latt

Paolo Cea, Leonardo Cosmai, Antonio D. Polosa

We apply the finite size scaling analysis to the derivative of the density of the effective action for the lattice U(1) pure gauge theory in an external constant magnetic field. We found the presence of a continuous phase transition. Moreover, our extimate of of the critical parameters gives values consistent with those extracted from the analysis of the spe

OBELIX Collaboration

The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+ pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen target are presented. It was found that the value of this ratio increases with the decreasing of the dipion mass, which demonstrates the difference in the phi and omega production mechanisms. An indication

Dieter Roehrich, NA35 Collaboration

Rapidity distributions of net hyperons ($Λ- \overlineΛ$) are compared to distributions of participant protons ($p - \overline{p}$). Strangeness production (mean multiplicities of produced $Λ/Σ^0$ hyperons and $\langle K + \overline{K} \rangle$) in central nucleus-nucleus collisions is shown for different collision systems at different energies. An enhanced p

Tsvi Piran

Gamma ray Bursts (GRBs) - short bursts of few hundred keV $γ$-rays - have fascinated astronomers since their accidental discovery in the sixties. GRBs were ignored by most relativists who did not expect that they are associated with any relativistic phenomenon. The recent observations of the BATSE detector on the Compton GRO satellite have revolutionized our

H. G. Evertz, D. P. Landau

Using spin-dynamics techniques we have performed large-scale computer simulations of the dynamic behavior of the classical three component XY-model (i.e. the anisotropic limit of an easy-plane Heisenberg ferromagnet), on square lattices of size up to 192^2, for several temperatures below, at, and above T_KT. The temporal evolution of spin configurations was

Claude Bourbonnais, Benoit Dumoulin

A theoretical approach to the influence of one-dimensional lattice fluctuations on electronic properties in weakly localized spin-Peierls systems is proposed using the renormalization group and the functional integral techniques. The interplay between the renormalization group flow of correlated electrons and one-dimensional lattice fluctuations is taken int

A. W. Garrett, S. E. Nagler, T. Barnes, B. C. Sales

In this letter we report results from inelastic neutron scattering experiments on powder samples of vanadyl pyrophosphate, (VO)2P2O7. We see evidence for three magnetic excitations, at 3.5 meV, 6.0 meV and 14 meV. The intensity of the 3.5 meV mode is strong near Q=0.8 A-1, consistent with the one-magnon gap mode reported previously and predicted by the spin-

Christian Helm, Joachim Keller

We start from the Barnes-Coleman slave-particle description, where the Hubbard operators $X$ are decomposed into a product of fermionic ($f_α$) and bosonic ($b$) operators. The quantum mechanical constraint $b^{\dagger} b + \sum_α f_α^{\dagger} f_α = 1$ is treated within the framework of Dirac&#39;s method for the quantization of classical constrained system

Samuele Bottani

In this article we study the behavior of globally coupled assemblies of a large number of Integrate and Fire oscillators with excitatory pulse-like interactions. On some simple models we show that the additive effects of pulses on the state of Integrate and Fire oscillators are sufficient for the synchronization of the relaxations of all the oscillators. Thi

F. M. Izrailev, T. Kottos, G. P. Tsironis

We study scaling properties of the localized eigenstates of the random dimer model in which pairs of local site energies are assigned at random in a one dimensional disordered tight-binding model. We use both the transfer matrix method and the direct diagonalization of the Hamiltonian in order to find how the localization length of a finite sample scales to

M. C. J. M. Vissenberg, M. J. M. de Jong

The interplay of migration, recombination, and dissociation of excitons in disordered media is studied theoretically in the low temperature regime. An exact expression for the photoluminescence spectrum is obtained. The theory is applied to describe the electric field-induced photoluminescence-quenching experiments by Kersting et al. [Phys. Rev. Lett. 73, 14

K. Takano, K. Kubo, H. Sakamoto

We examine the ground state of a Heisenberg model with arbitrary spin S on a one-dimensional lattice composed of diamond-shaped units. A unit includes two types of antiferromagnetic exchange interactions which frustrate each other. The system undergoes phase changes when the ratio $λ$ between the exchange parameters varies. In some phases, strong frustration

M. Buttiker, T. Christen

In the framework of the edge-channel picture and the scattering approach to conduction, we discuss the low frequency admittance of quantized Hall samples up to second order in frequency. The first-order term gives the leading order phase-shift between current and voltage and is associated with the displacement current. It is determined by the emittance which

Hisatoshi Yokoyama, Masao Ogata

Two-dimensional t-J model is studied by a variational Monte Carlo method, using Gutzwiller-Jastrow-type wave functions. Various kinds of superconducting pairing symmetries are compared in order to determine the phase diagram of the ground state in the full J/t-n plane. Near the half filling where the high temperature superconductivity is expected, the d_{x^2

Evelyne Viegas, Boyan Onyshkevych, Victor Raskin, Sergei Nirenburg

This paper deals with the discovery, representation, and use of lexical rules (LRs) during large-scale semi-automatic computational lexicon acquisition. The analysis is based on a set of LRs implemented and tested on the basis of Spanish and English business- and finance-related corpora. We show that, though the use of LRs is justified, they do not come cost