May 1997 arXiv papers — page 6

Carlo Rovelli, Thomas Thiemann

Barbero has generalized the Ashtekar canonical transformation to a one-parameter scale transformation $U(ι)$ on the phase space of general relativity. Immirzi has noticed that in loop quantum gravity this transformation alters the spectra of geometrical quantities. We show that $U(ι)$ is a canonical transformation that cannot be implement unitarily in the qu

Vladimir Pestov

This small survey of basic universal constructions related to the actions of topological groups on compacta is centred around a new result --- an intrinsic description of extremely amenable topological groups (i.e., those having a fixed point in each compactum they act upon), solving a 1967 problem by Granirer. Another old problem whose solution (in the nega

Peter Neu, David R. Reichman, Robert J. Silbey

A dynamical theory is constructed to describe spectral diffusion in glasses in the temperature range near 1 Kelvin on long time scales. The theory invokes interacting tunneling centers (TLS) which provide an excess contribution to the spectral hole width which qualitatively accounts for the deviation from standard logarithmic line broadening observed by Maie

K. Okano, L. Schuelke, K. Yamagishi, B. Zheng

Dynamic relaxation of the XY model quenched from a high temperature state to the critical temperature or below is investigated with Monte Carlo methods. When a non-zero initial magnetization is given, in the short-time regime of the dynamic evolution the critical initial increase of the magnetization is observed. The dynamic exponent $θ$ is directly determin

Benjamin P. Lee, Michael E. Fisher

The recent generalized Debye-Hueckel (GDH) theory is applied to the calculation of the charge-charge correlation function G_{ZZ}(r). The resulting expression satisfies both (i) the charge neutrality condition and (ii) the Stillinger-Lovett second-moment condition for all T and rho_N, the overall ion density, and (iii) exhibits charge oscillations for densiti

Z. B. Li, X. W. Liu, L. Schuelke, B. Zheng

We simulate the kinetic Ashkin-Teller model with both ordered and disordered initial states, evolving in contact with a heat-bath at the critical temperature. The power law scaling behaviour for the magnetic order and electric order are observed in the early time stage. The values of the critical exponent $θ$ vary along the critical line. Another dynamical e

B. Zheng

The short-time behaviour of the critical dynamics for magnetic systems is investigated with Monte Carlo methods. Without losing the generality, we consider the relaxation process for the two dimensional Ising and Potts model starting from an initial state with very high temperature and arbitrary magnetization. We confirm the generalized scaling form and obse

L. Schuelke, B. Zheng

The scaling behaviour of the persistence probability in the critical dynamics is investigated with both the heat-bath and the Metropolis algorithm for the two-dimensional Ising model and Potts model. Special attention is drawn to the dependence on the initial magnetization. The global persistence exponent is measured. Universality is confirmed.

C. Monthus, O. Golinelli, Th. Jolicoeur

We give a physical description in terms of percolation theory of the phase transition that occurs when the disorder increases in the random antiferromagnetic spin-1 chain between a gapless phase with topological order and a random singlet phase. We study the statistical properties of the percolation clusters by numerical simulations, and we compute exact exp

Pep Español

We present a generalization of dissipative particle dynamics that includes shear forces between particles. The new algorithm has the same structure as the (isothermal) smoothed particle dynamics algorithm, except that it conserves angular momentum and includes thermal fluctuations consistently with the principles of equilibrium statistical mechanics. This cl

Pablo M. Gleiser, Francisco A. Tamarit

The spreading of damage technique is used to study the sensibility to initial conditions in a heath bath Monte Carlo simulation of the spin glass hypercubic cell model. Since the hypercubic cell in dimension 2D and the hypercubic lattice in dimension D resemble each other closely at finite dimensions and both converge to mean field when dimension goes to inf

Alexander Altland, Martin Janssen, Boris Shapiro

We study an ensemble of random matrices (the Rosenzweig-Porter model) which, in contrast to the standard Gaussian ensemble, is not invariant under changes of basis. We show that a rather complete understanding of its level correlations can be obtained within the standard framework of diagrammatic perturbation theory. The structure of the perturbation expansi

R. Coldea, D. A. Tennant, R. A. Cowley, D. F. McMorrow

Magnetic excitations of the quasi-1D S=1/2 Heisenberg antiferromagnet (HAF) Cs2CuCl4 have been measured as a function of magnetic field using neutron scattering. For T<0.62 K and B=0 T the weak inter-chain coupling produces 3D incommensurate ordering. Fields greater than Bc =1.66 T, but less than the field (~8 T) required to fully align the spins, are observ

Frank K. Wilhelm, Andrei D. Zaikin, Herve Courtois, .

We study the transport properties of a quasi-two-dimensional diffusive normal metal film attached to a superconductor. We demonstrate that the properties of such films can essentially differ from those of quasi-one-dimensional systems: in the presence of the proximity induced superconductivity in a sufficiently wide film its conductance may not only increase

M. Abolfath, M. R. Ejtehadi

We report the application of the nonlinear $σ$ model to study the multi-skyrmion problem in the quantum Hall ferromagnet system. We show that the ground state of the system can be described by a ferromagnet triangular Skyrme lattice near $ν=1$ where skyrmions are extremely dilute. We find a transition into antiferromagnet square lattice by increasing the sky

H. J. Luo, L. Schuelke, B. Zheng

With Monte Carlo methods we investigate the dynamic relaxation of the fully frustrated XY model in two dimensions below or at the Kosterlitz-Thouless phase transition temperature. Special attention is drawn to the sublattice structure of the dynamic evolution. Short-time scaling behaviour is found and universality is confirmed. The critical exponent $θ$ is m

K. Okano, L. Schuelke, B. Zheng

The dynamic relaxation process for the (2+1)--dimensional SU(2) lattice gauge theory at critical temperature is investigated with Monte Carlo methods. The critical initial increase of the Polyakov loop is observed. The dynamic exponents $θ$ and $z$ as well as the static critical exponent $β/ν$ are determined from the power law behaviour of the Polyakov loop,

Peter A. Heeman, James F. Allen

Language models for speech recognition tend to concentrate solely on recognizing the words that were spoken. In this paper, we redefine the speech recognition problem so that its goal is to find both the best sequence of words and their syntactic role (part-of-speech) in the utterance. This is a necessary first step towards tightening the interaction between

R. Vilela Mendes

The challenging problems, in the field of control of chaos or of transition to chaos, lie in the domain of infinite-dimensional systems. Access to all variables being impossible in this case and the controlling action being limited to a few collective variables, it will not in general be possible to drive the whole system to the desired behaviour. A paradigm

Buell T. Jannuzi, Alan P. Marsher, Martin Pohl, Alex G. Smith

Four parallel workshops were organized at the 1996 Girona Conference, &#34;Blazars, Black Holes, and Jets&#34;, with conference attendees free to choose which session they would like to attend. The chosen topics were ``Jet Models&#39;&#39;, ``Multi-Frequency Support for High-Energy Observations&#39;&#39;, ``Monitoring of Blazars&#39;&#39;, and ``Host Galaxie

Susan E. Ridgway, Alan Stockton

We present the results of an HST and ground-based imaging study of a complete 3C sample of z ~ 1 sources, including 5 quasars and 5 radio galaxies. We have resolved continuum structure around all of our quasars in the WFPC2 images and in four of the five ground-based K&#39; images. All of the quasars have some optical continuum structure that is aligned with

K. Nilsson, J. Heidt, T. Pursimo, L. O. Takalo

We have detected an optical jet in the BL Lac object 3C 371 that coincides with the radio jet in this object in the central few kpc. The most notable feature is a bright optical knot 3 arcsec (4 kpc) from the nucleus that occurs at the location where the jet apparently changes its direction by ~30 degrees. The radio, near-infrared and optical observations of

Albert Stebbins

A short review of the measured spectrum of the Cosmic Microwave Background Radiation (CMBR) and implications. Extensions of the Kompaneets equation and Sunyaev-Zel&#39;dovich effect are given.

Montserrat Teixidor-i-Bigas

This paper considers curves in Grassmannians which are themselves immersed in projective space by the Plucker map. It is shown that for a generic vector bundle of high enough degree, the image curve lies in a proper linear subvariety of this projective space and satisfies good conditions on syzygies as a curve in this subspace. For very small degree and gene

Montserrat Teixidor-i-Bigas

Let C be an algebraic curve of genus g. Let E be a vector bundle of rank n and degree d. Consider among all subbundles F&#39; of E of rank n&#39; those of maximal degree d&#39;. Then s_n&#39;(E)= n&#39;d-nd&#39;\le n&#39;(n-n&#39;)g. If E is stable s_n&#39;(E)>0 while if E is generic s_n&#39;(E)\ge n&#39;(n-n&#39;)(g-1) . The following statement was conjectu

Chih-Lung Chou

The N=1 supersymmetric gauge SU(5) theory with one antisymmetric tensor, n+3 fundamentals and n+4 antifundamentals has dual magnetic descriptions in the infrared. By introducing extra singlet fields and tree level superpotential terms to the electric SU(5) theories, we are able to make the dual theories flow to the known SU(n)xSU(2) gauge theories which brea

J. L. Friar, G. L. Payne

Nuclear-size corrections of order $(Z α)^5$ and $(Z α)^6$ to the S-state levels of hydrogenic atoms are considered. These nuclear-elastic contributions are somewhat smaller than the polarizability (nuclear-inelastic) corrections for deuterium, but are of comparable or larger size for the hydrogen case. For deuterium the (attractive) nonrelativistic $(Z α)^5$

C. M. Hull

It is argued that D=10 type II strings and M-theory in D=11 have D-5 branes and 9-branes that are not standard p-branes coupled to anti-symmetric tensors. The global charges in a D-dimensional theory of gravity consist of a momentum $P_M$ and a dual D-5 form charge $K_{M_1...M_{D-5}}$, which is related to the NUT charge. On dimensional reduction, P gives the

J. M. Kommers, W. H. G. Lewin, C. Kouveliotou, J. van Paradijs

We describe a search of archival data from the Burst and Transient Source Experiment (BATSE). The purpose of the search is to find astronomically interesting transients that did not activate the burst detection (or ``trigger&#39;&#39;) system onboard the spacecraft. Our search is sensitive to events with peak fluxes (on the 1.024 s time scale) that are lower

Q. P. Liu, M. Manas

We consider the vectorial approach to the binary Darboux transformations for the Kadomtsev-Petviashvili hierarchy in its Zakharov-Shabat formulation. We obtain explicit formulae for the Darboux transformed potentials in terms of Grammian type determinants. We also study the $n$-th Gel&#39;fand-Dickey hierarchy introducing spectral operators and obtaining sim

JM Figueroa-O&#39;Farrill, C Koehl, B Spence

The cohomology of a compact Kaehler (resp. hyperKaehler) manifold admits the action of the Lie algebra so(2,1) (resp. so(4,1)). In this paper we show, following an idea of Witten, how this action follows from supersymmetry, in particular from the symmetries of certain supersymmetric sigma models. In addition, many of the fundamental identities in Hodge-Lefsc

P. K. Townsend

A manifestly S-dual, and `12 dimensional&#39;, IIB superstring action with an $Sl(2;\bR)$ doublet of `Born-Infeld&#39; fields is presented. The M-theory origin of the 12th dimension is the M-2-brane tension, which can be regarded as the flux of a 3-form worldvolume field strength. The latter is required by the fact that the M-2-brane can have a boundary on a

Nikolaos Stergioulas, John L. Friedman

We study nonaxisymmetric perturbations of rotating relativistic stars. modeled as perfect-fluid equilibria. Instability to a mode with angular dependence $\exp(imϕ)$ sets in when the frequency of the mode vanishes. The locations of these zero-frequency modes along sequences of rotating stars are computed in the framework of general relativity. We consider mo

Paul Biran

We prove a gluing theorem which allows to construct an ample divisor on a rational surface from two given ample divisors on simpler surfaces. This theorem combined with the Cremona action on the ample cone gives rise to an algorithm for constructing new ample divisors. We then propose a conjecture relating continued fractions approximations and Seshadri-like

Sukyoung Yi, Pierre Demarque, Augustus Oemler,

We present models of the late stages of stellar evolution intended to explain the UV upturn phenomenon in elliptical galaxies. Such models are sensitive to values of a number of poorly-constrained physical parameters, including metallicity, age, stellar mass loss, helium enrichment, and the distribution of stars on the zero age horizontal branch (HB). We exp

P. Osland, A. A. Pankov

New observables σ_\pm for the process e^+e^-\toμ^+μ^- allow one to get more direct information on additional Z&#39; boson effects than what is obtained from the canonical ones, σand A_{FB}. Their deviations from the Standard Model predictions have very specific energy dependences, which are precisely determined by SM parameters. At energies varying from TRIS

Koji Harada, Thomas Heinzl, Christian Stern

We investigate the mesonic light-front bound-state equations of the &#39;t Hooft and Schwinger model in the two-particle, i.e. valence sector, for small fermion mass. We perform a high precision determination of the mass and light-cone wave function of the lowest lying meson by combining fermion mass perturbation theory with a variational approach. All calcu

P V Landshoff

Within the next few years experiments at RHIC and the LHC will seek to create in the laboratory a quark-gluon plasma, the phase of matter in which the Universe was initially created. It is believed that the plasma will survive long enough to reach thermal equilibrium. I give an introduction to the formalism of thermal field theory, the combination of statist

Robert S. Plant, Michael C. Birse

We consider a nonlocal version of the NJL model, based on a separable quark-quark interaction. The interaction is extended to include terms that bind vector and axial-vector mesons. The nonlocality means that no further regulator is required. Moreover the model is able to confine the quarks by generating a quark propagator without poles at real energies. Wor

D. P. Roy

The H1 and ZEUS experiments at the HERA $e^\pm p$ collider at Hamburg have recently reported some anomalous hard-scattering events, which could be indicative of new physics beyond the standard model. I have tried to discuss in a nonspecialist language the significance of this result for particle physics along with its interpretation in terms of the currently

James E. Rhoads

If gamma ray bursts are highly collimated, the energy requirements of each event may be reduced by several (~ 4-6) orders of magnitude, and the event rate increased correspondingly. Extreme conditions in gamma ray bursters lead to highly relativistic motions (bulk Lorentz factors Gamma > 100). This results in strong forward beaming of the emitted radiation i

Hisatoshi Yokoyama, Yasuhiro Saiga

Spin dynamics as well as static properties of the one-dimensional J-J&#39; model (S=1/2, J>0 and 0\le α=J&#39;/J\le 0.5) are studied by the exact diagonalization and the recursion method of finite systems up to 26 sites. Especially, the dynamical structure factor S(q,ω) is investigated carefully for various values of α. As αincreases beyond the gapless-gapfu

Conor Houghton, Nicholas Manton, Paul Sutcliffe

We discuss the similarities between BPS monopoles and Skyrmions, and point to an underlying connection in terms of rational maps between Riemann spheres. This involves the introduction of a new ansatz for Skyrme fields. We use this to construct good approximations to several known Skyrmions, including all the minimal energy configurations up to baryon number

Kedar Damle, Subir Sachdev

We describe the nature of charge transport at non-zero temperatures ($T$) above the two-dimensional ($d$) superfluid-insulator quantum critical point. We argue that the transport is characterized by inelastic collisions among thermally excited carriers at a rate of order $k_B T/\hbar$. This implies that the transport at frequencies $ω\ll k_B T/\hbar$ is in t

Alexei Ashikhmin

We present some results that show that bounds from classical coding theory still work in many cases of quantum coding theory.

A. E. Allahverdyan, D. B. Saakian

The strengthened data processing inequality have been proved. The general theory have been illustrated on the simple example.

G. Drobny, B. Hladky

We consider a trapped ion with a quantized center-of-mass motion in 2D trap potential. With external laser fields the effective (non)linear coupling of two orthogonal vibrational modes can be established via stimulated Raman transition. Nonclassical vibrational states such as squeezed states or two-mode entangled states (Schroedinger cat-like states) can be

Paolo Sibani

We consider a continuum version of a previously introduced and numerically studied model of macroevolution (PRL 75, 2055, (1995)) in which agents evolve by an optimization process in a rugged fitness landscape and die due to their competitive interactions. We first formulate dynamical equations for the fitness distribution and the survival probability. Secon

Joel A. Shapiro

I discuss issue of how to adjust recitation grades given by different instructors in a large course, taking into account and correcting for differences in standards among the instructors, while preserving the effects of differences in average student performance among the recitation sections.

R. M. Davidson, N. C. Mukhopadhyay

We comment on the recent Mainz &#34;measurement&#34; (PRL78 (1997) 606) of the $E2/M1$ ratio in the $N-Δ$ electromagnetic transition. Analyzing the Mainz data using an effective Lagrangian approach, we find this ratio to be (-3.19$\pm$0.24)%.

N. C. Mukhopadhyay, R. M. Davidson

We shall review here our current knowledge and new frontiers of the pion photoproduction study, from threshold through the Delta resonance region, emphasizing the hadron physics program, of interest to a 250 MeV, high duty factor electron facility, such as the upgraded MAX-lab at the Lund University, Sweden, where it would be possible to produce tagged photo

V. R. Manfredi, L. Salasnich

In atomic nuclei, as in other many-body systems, the classical phase space is mixed, so ordered and chaotic states generally coexist. In this contribution we discuss some models, showing the transition from order to chaos. In several cases a clear correspondence between classical and quantum chaos has been established. In particular the transition from order

R. Beck, H. P. Krahn

We reply to the Comment of R.L. Workman on the E2/M1 ratio from the Mainz photoproduction data, nucl-th/9702052. We support our published result for the E2/M1 ratio of REM = -(2.5 +- 0.2 +- 0.2)%.

Alejandro Adem, Dikran Karagueuzian, R. James Milgram, K. Umland

We compute the mod 2 cohomology of the sporadic simple group Ly as well as that of the double covers of the alternating groups A_8 and A_10.

Sumit R. Das

The entropy of a near-extremal black hole made of parallel D-branes has been shown to agree, upto a numerical factor, with that of the gas of massless open string states on the brane worldvolume when the string coupling is chosen suitably. We investigate the process of emission or absorption of massless S-wave neutral scalars by these black holes. We show th

Jiro Arafune, Kenzo Ogure, Joe Sato

We calculate the effective potential of the scalar theory at finite temperature under the super-daisy approximation, after expressing its derivative with respect to mass square in terms of the full propagator. This expression becomes the self-consistent equation for the derivative of the effective potential. We find the phase transition is first order with t

J. Barcelos-Neto, W. Oliveira

We use an extension of the method due to Batalin, Fradkin, Fradkina, and Tyutin (BFFT) for transforming the nonlinear $σ$ model in a non-Abelian gauge theory. We deal with both supersymmetric and nonsupersymmetric cases. The bosonic case was already considered in literature but just gauged with an Abelian algebra. We show that the supersymmetric version is o

David Alba, Luca Lusanna

The system of N scalar particles with Grassmann-valued color charges plus the color SU(3) Yang-Mills field is reformulated on spacelike hypersurfaces. The Dirac observables are found and the physical invariant mass of the system in the Wigner-covariant rest-frame instant form of dynamics (covariant Coulomb gauge) is given. From the reduced Hamilton equations

David Alba, Luca Lusanna

After a summary of a recently proposed new type of instant form of dynamics (the Wigner-covariant rest-frame instant form), the reduced Hamilton equations in the covariant rest-frame Coulomb gauge for the isolated system of N scalar particles with pseudoclassical Grassmann-valued electric charges plus the electromagnetic field are studied. The Lienard-Wieche

Luca Lusanna

Talk at the International Workshop ``New Non Perturbative Methods and Quantization on the Light Cone&#34;, Les Houches February 24 - March 7, 1997.

Ali H. Chamseddine

A supersymmetric theory in two-dimensions has enough data to define a noncommutative space thus making it possible to use all the tools of noncommutative geometry. In particular, we apply this to the N=1 supersymmetric non-linear sigma model and derive an expression for the generalized loop space Dirac operator, in presence of a general background, using can

Nobuhito Maru, Jun Nishimura

We present a lattice formulation which gives super Yang-Mills theories in any dimensions with simple supersymmetry as well as extended supersymmetry in the continuum limit without fine-tuning. We first formulate super Yang-Mills theories with simple supersymmetry in 3,4,6,10 dimensions, incorporating the gluino on the lattice using the overlap formalism. In

Michael Dine, Antonio Riotto

Inflation, as currently understood, requires the presence of fields with very flat potentials. Supersymmetric models in which supersymmetry breaking is communicated by supergravity naturally yield such fields, but the scales are typically not suitable for obtaining both sufficient inflation and a suitable fluctuation spectrum. In the context of recent ideas

Eric Laenen

We discuss the resummation of Sudakov effects in a cross section from the viewpoint of its underlying factorization near the edge of phase space. We perform the resummation of Sudakov threshold logarithms in Higgs (Standard Model and Minimal Supersymmetric SM) production at the LHC, using an evolution equation in the Higgs mass that is derived from this fact

William B. Kilgore

I present results from a next-to-leading order event generator of purely gluonic jet production. This calculation is the first step in the construction of a full next-to-leading order calculation of three jet production at hadron colliders. Several jet algorithms commonly used in experiments are implemented and their numerical stability is investigated. A nu

Christopher D. Carone, Lawrence J. Hall, Takeo Moroi

We present a class of supersymmetric models in which flavor symmetries are broken dynamically, by a set of composite flavon fields. The strong dynamics that is responsible for confinement in the flavor sector also drives flavor symmetry breaking vacuum expectation values, as a consequence of a quantum-deformed moduli space. Yukawa couplings result as a power

Gordon L. Kane

Although no individual piece of experimental evidence for supersymmetry is compelling so far, several are about as good as they can be with present errors. Most important, all pieces of evidence imply the same values for common parameters --- a necessary condition, and one unlikely to hold if the hints from data are misleading. The parameters are sparticle o

Jiri Chyla, Jiri Rames

For theoretically consistent determination of $α_s$ from jet rates in deep inelastic scattering the dependence on $α_s$ of parton distribution functions is in principle as important as that of hard scattering cross-sections. For the kinematical region accessible at HERA we investigate in detail numerical importance of these two sources of the $α_s$ dependenc

J. Ambjorn, A. Krasnitz

We determine the sphaleron transition rate using real time lattice simulations of the classical system. An improved definition of the lattice topological charge allows us to obtain a more reliable estimate of the transition rate. For an SU(2) Yang-Mills-Higgs system in the broken phase we find the transition rate to be strongly suppressed, and we have observ

Barbara Mele

The main physics topics of interest at LEP2, the CERN electron-positron collider with center-of-mass energy in the range (161-192) GeV, are reviewed. Progresses in both the precision tests of the standard model and the field of discovery physics attainable at this machine are discussed. A few results of the analysis of data collected in the 1996 first runs o

S. M. Troshin, N. E. Tyurin

We consider low-$x$ behaviour of the spin structure functions $g_1(x)$ and $h_1(x)$ in the unitarized chiral quark model which combines ideas on the constituent quark structure of hadrons with a geometrical scattering picture and unitarity. A nondiffractive singular low-$x$ dependence of $g^p_1(x)$ and $g_1^n(x)$ indicated by the recent SMC experimental data

Eugene Levin

This talk is a digest of Ref.[1](E.Gotsman,E. Levin and U. Maor: TAUP 2416/97, hep-ph/9705205,Phys. Lett. (in press)) where a new mechanism for hard inclusive production, which leads to a violation of the factorization theorem (FT), is suggested. Numericalestimates for the effect are given for high energy hadron (nucleus) scattering.

Edward Boos, Thorsten Ohl

We propose a general classification of all four fermion final states in $γγ$ collisions at a future $e^+e^-$ Linear Collider and discuss the relation of ``signal&#39;&#39; and ``background&#39;&#39; contributions in vector boson production. We utilize the results in a critical examination of the Higgs signal in sub-threshold $W^+W^-$ pair production.

J. Matias

A new type of gauge extension of the SM is proposed. It is based on a SU(2)xSU(2)xU(1) group with the peculiarity that the gauge bosons of the extra SU(2) do not couple to fermions. This feature relaxes some of the constraints on the masses of the new gauge bosons, leaving the possibility of having lighter masses than in traditional extensions. The model exh

Akihiro Murayama

A D-parity violated SUSY SU(4) x SU(2) _ L x SU(2)_R gauge model with the Higgs sector 2{(4,1,2)+(4-bar,1, 2)}+(1,2,2)+some(1,1,1)&#39;s is shown to have the following advantages: (i) It is the simplest and almost unique solution that satisfies M_X = M_{string} ~0.6 x 10^{18} GeV and M_{INT} ~ 5 x10^{11} GeV in superstring derived SUSY SO(10) GUTs. (ii) The

G. Buchalla

A brief review of the theoretical status of CP violation in decays of neutral kaons is presented. We focus on three important topics: $\varepsilon$, $\varepsilon&#39;/\varepsilon$ and $K_L\toπ^0ν\barν$.

Robert D. Mawhinney

We have measured the hadron spectrum in lattice QCD, using staggered fermions, for 0 (the quenched approximation), 2 and 4 light degenerate dynamical quarks. In addition to earlier results involving extrapolations in valence quark masses for fixed dynamical mass, we also report results where we extrapolate in the dynamical mass for 4 flavors. We see a marked

Robert D. Mawhinney

We have done simulations of lattice QCD with different numbers of light dynamical quarks. Since we cannot reach the continuum limit with our current computers, we have done comparisons with 0 (quenched), 2 and 4 light quark flavors with the physical volume and lattice spacing constant, when these are determined from the mass of the rho. We find a 7% (2 stand

Dong Chen, Robert D. Mawhinney

We have studied the hadron spectrum while varying the number of light dynamical quarks when the physical lattice spacing and volume are held fixed relative to the rho mass. For two and zero flavors of staggered fermions, we find the nucleon to rho mass ratios (extrapolated to zero valence quark mass) are very similar. However, for four flavors the ratio is 7

Robert D. Mawhinney

We present a summary of the progress on QCDSP in the last year. QCDSP, Quantum Chromodynamics on Digital Signal Processors, is an inexpensive computer being built at Columbia that can achieve 0.8 teraflops for three million dollars.

D. Espriu, V. Koulovassilopoulos, A. Travesset

Motivated by the issue of whether it is possible to construct phenomenologically viable models where the electroweak symmetry breaking is triggered by new physics at a scale $Λ\gg 4πv$, where $v$ is the order parameter of the transition ($v\sim 250$ GeV) and $Λ$ is the scale of new physics, we have studied the phase diagram of the $U(2) \times U(2)$ model. T

Rainer Sommer

We review the O(a) improvement of lattice QCD with special emphasis on the motivation for performing the improvement programme non-perturbatively and the general concepts of on-shell improvement. The present status of the calculations of various improvement coefficients (perturbative and non-perturbative) is reviewed, as well as the computation of the isospi

T. R. Klassen

The Schrödinger Functional (quantum/lattice field theory with Dirichlet boundary conditions) is a powerful tool in the non-perturbative improvement and for the study of other aspects of lattice QCD. Here we adapt it to improved gluon and quark actions, on isotropic as well as anisotropic lattices. Specifically, we describe the structure of the boundary layer

D0 Collaboration, B. Abbott

We report on a search for the trilepton signature from the associated production of supersymmetric gaugino pairs, Chi_1^(+-) Chi_2^0, within the context of minimal supersymmetric models that conserve R-parity. This search uses 95 pb^-1 of data taken with the \D0 detector at Fermilab&#39;s Tevatron collider at \sqrt{s} = 1.8 TeV. No evidence of a trilepton si

C. Adloff

The electroproduction of rho mesons with proton diffractive dissociation for Q^2 > 7 GeV^2 and the elastic electroproduction of Phi mesons for Q^2 > 6 Gev^2 are studied in e^+ p collisions at HERA with the H1 detector, for an integrated luminosity of 2.8 pb-1. The dependence of the cross sections on P_t^2 and Q^2 is measured, and the vector meson polarisatio

G. Giachetta, L. Mangiarotti, G. Sardanashvily

Building on the universal covering group of the general linear group, we introduce the composite spinor bundle whose subbundles are Lorentz spin structures associated with different gravitational fields. General covariant transformations of this composite spinor bundle are canonically defined.

Sukratu Barve, T. P. Singh

By now, many examples of naked singularities in classical general relativity are known. It may however be that a physical principle over and above the general theory prevents the occurrence of such singularities in nature. Assuming the validity of the Weyl curvature hypothesis, we propose that naked singularities are forbidden by the second law of thermodyna

B. V. Ivanov

A coordinate transformation is found which diagonalizes the axisymmetric pp-waves. Its effect upon concrete solutions, including impulsive and shock waves, is discussed.

Takahiro Tanaka, Masa-aki Sakagami

Taking into account the effect of self-interaction, the dynamics of the quantum fluctuations of the inflaton field with $λϕ^4$ potential is studied in detail. We find that the self interaction efficiently drives the initial pure state into a mixed one, which can be understood as a statistical ensemble. Further, the expectation value of the squared field oper

G. Burdet, M. Perrin

Twenty years ago, by extending the Wightman axiom framework, it has been found possible to quantize only a conformal factor of the gravitational field. Gravitons being excluded from this quantum scalar field theory, numerous attempts were done to give a valuable description of what could be quantum gravity. In this talk we present a familly of Lorentz manifo

M. Reza Sadr-Lahijany, Purusattam Ray, H. Eugene Stanley

We perform extensive simulations of $10^4$ Lennard-Jones particles to study the effect of particle size dispersity on the thermodynamic stability of two-dimensional solids. We find a novel phase diagram in the dispersity-density parameter space. We observe that for large values of the density there is a threshold value of the size dispersity above which the

P. S. Kuhn, A. Diehl, Y. Levin, M. C. Barbosa

A melting transition for a system of hard spheres interacting by a repulsive Yukawa potential of DLVO form is studied. To find the location of the phase boundary, we propose a simple theory to calculate the free energies for the coexisting liquid and solid. The free energy for the liquid phase is approximated by a virial expansion. The free energy of the cry

C. P. Burgess, C. A. Lutken

We set up the effective field theories which describe the SO(5)-invariant picture of the high-Tc cuprates in various regimes. We use these to get quantitative conclusions concerning the size of SO(5)-breaking effects. We consider two applications in detail: (i) the thermodynamic free energy, which describe the phase diagram and critical behaviour, and (ii) t

Ghyslain Boisvert, Laurent J. Lewis, Matthias Scheffler

The results of a density-functional-theory study of the formation energies of (100)- and (111)-faceted steps on the Pt(111) surface, as well as of the barrier for diffusion of an adatom on the flat surface, are presented. The step formation energies are found to be in a ratio of 0.88 in favour of the (111)-faceted step, in excellent agreement with experiment

Felix Ritort

In this letter a new solvable model of synchronization dynamics is introduced. It consists of a system of long range interacting tops with random precession frequencies. The model allows for an explicit study of orientational effects in synchronized phenomena. A stability analysis of the incoherent solution is performed for different types of orientational d

Laurent J. Lewis, Alessandro De Vita, Roberto Car

We report detailed and extensive first-principles molecular-dynamics (MD) simulations of the structure and electronic properties of amorphous InP produced by rapid quenching from the liquid. The structure of the material is found to be strongly ordered chemically, even though there is a significant number of coordination defects and despite the presence of o

Michele Vendruscolo, Edo Kussell, Eytan Domany

We present an efficient algorithm to recover the three dimensional structure of a protein from its contact map representation. First we show that when a physically realizable map is used as target, our method generates a structure whose contact map is essentially similar to the target. Furthermore, the reconstructed and original structures are similar up to

Nicola Manini, Michel van Veenendaal, Massimo Altarelli

Although the Ni_4 cluster includes more information regarding the Ni band structure with respect to the Anderson impurity model, it also favors very peculiar ground states which are incompatible with a coherent picture of all dichroism experiments.

Jan de Gier, Bernard Nienhuis

We show that a rectangle triangle random tiling with a tenfold symmetric phase is solvable by Bethe Ansatz. After the twelvefold square triangle and the eightfold rectangle triangle random tiling, this is the third example of a rectangle triangle tiling which is solvable. A Bethe Ansatz solution provides in principle an accurate estimate of the entropy and p

D. Springsguth, R. Ketzmerick, T. Geisel

We study the energy spectrum and the quantized Hall conductance of electrons in a two-dimensional periodic potential with perpendicular magnetic field WITHOUT neglecting the coupling of the Landau bands. Remarkably, even for weak Landau band coupling significant changes in the Hall conductance compared to the one-band approximation of Hofstadter&#39;s butter