Wed·Sep 28, 2005Wednesday·September 28, 2005

1. 01*

   Perturbative renormalisation of the chiral Gross-Neveu model

   Bjorn Leder🇩🇪 · Tomasz Korzec🇩🇪

   We study the chiral Gross-Neveu model with Wilson fermions. In the framework of the Schroedinger functional we show that in general not only the bare mass has to be tuned to achieve chiral symmetry in the continuum, but also coupling constants multiplying chirally non-invariant four fermion terms. The strategy for fixing the parameters of the theory is explained in perturbation theory and the results of a first order calculation are presented. The results are shown to agree with the infinite flavour limit.

   hep-latPoS(2006)·2 citations
2. 02*

   Anisotropic lattice QCD study of pentaquark baryons in spin 3/2 channel

   Takumi Doi (RIKEN BNL)🇺🇸 · Noriyoshi Ishii (Tokyo Inst. Tech.)🇯🇵 · Yukio Nemoto (Nagoya Univ.)🇯🇵 · Makoto Oka (Tokyo Inst. Tech.)🇯🇵 · Hideo Suganuma (Kyoto Univ.)🇯🇵

   We perform the comprehensive analysis of the pentaquark (5Q) in J^P=3/2^{\pm} channel using anisotropic quenched lattice QCD. We employ the standard Wilson gauge action at \beta=5.75 and the O(a) improved Wilson (clover) quark action on a 12^3*96 lattice with the renormalized anisotropy as a_s/a_t = 4. A large number of gauge configurations as Nconf=1000 is analyzed, which is found to be essential to achieve a reliable measurement. We study three types of the Rarita-Schwinger intepolationg fields with I=0: (a) the NK*-type, (b) the (color-)twisted NK*-type, (c) a diquark-type. As a result, we find only massive states as m(5Q)= 2.1-2.2 GeV in J^P=3/2^- channel, and m(5Q) = 2.4-2.6 GeV in J^P=3/2^+ channel in the chiral limit. The analysis with the hybrid boundary condition (HBC) is performed to distinguish whether these resonances are compact 5Q resonances or two-particle scattering states. No low-lying compact 5Q resonance states are found below 2.1GeV.

   hep-latPoS(2006)·1 citation
3. 03*

   The Scaling of QED in a Non-Commutative Space-Time

   J. Volkholz🇩🇪 · W. Bietenholz🇩🇪 · J. Nishimura🇯🇵 · Y. Susaki🇯🇵

   We present results of numerical simulations for pure U(1) gauge theory in a non-commutative space. The theory is mapped onto a dimensionally reduced matrix model, which renders its numerical treatment feasible. New data on large lattices reveal the scaling of Wilson loops and their correlation functions in the simultaneous limit to the continuum and to infinite volume, at fixed non-commutativity. In this on-going project we are particularly interested in the IR behaviour, the ``photo-ball'' spectrum and in the photon dispersion relation.

   hep-lathep-thPoS(2006)·6 citations
4. 04*

   A toy model of (grand) unified monopoles

   Lorenz von Smekal🇦🇺 · Torsten Tok🇩🇪 · Philippe de Forcrand🇨🇭

   We explore the old idea that, in a theory containing several gauge groups, the topological defects of one gauge group coincide with those of another gauge group. This simple 'unification' constraint has deep consequences, the best known of which is a natural explanation of the fractional electric charge of quarks. Here we explore the consequences of this idea for the phase diagram, in a toy model U(1)x U(1).

   hep-latPoS(2006)·5 citations
5. 05*

   Search for the S=+1 pentaquarks in quenched lattice QCD

   Toru T. Takahashi🇯🇵 · Takashi Umeda🇯🇵 · Tetsuya Onogi🇯🇵 · Teiji Kunihiro🇯🇵

   We study spin $\frac{1}{2}$ hadronic states in quenched lattice QCD to search for a possible $S=+1$ pentaquark resonance. Our work is the first systematic lattice QCD study which properly carries out the following analyses: {\it (1) the careful extraction of the first two low energy states with very high statistics and the variational method} and {\it (2) the study of volume dependences of eigenenergies and spectral weights to distinguish resonance states from scattering states}. Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices at $\beta$=5.7 with the standard plaquette gauge action and the Wilson quark action. Our result indicates the existence of a resonance state lying slightly above the NK threshold in $(I,J^P)=(0,{\frac{1}{2}}^{-})$ channel in quenched QCD.

   hep-latPoS(2006)·2 citations
6. 06*

   Leibniz rule and exact supersymmetry on lattice: a case of supersymmetrical quantum mechanics

   Mitsuhiro Kato🇯🇵 · Makoto Sakamoto🇯🇵 · Hiroto So🇯🇵

   We propose a new formulation of lattice theory. It is given by a matrix form and suitable for satisfying Leibniz rule on lattice. The theory may be interpreted as a multi-flavor system. By realizing the difference operator as a commutator, we may obtain exact supersymmetric theories on lattice explicitly. Some problems such as locality and single flavor reduction are also commented.

   hep-latPoS(2006)·11 citations
7. 07*

   Heavy quark free energies and screening at finite temperature and density

   M. Doring🇩🇪 · S. Ejiri🇯🇵 · O. Kaczmarek🇩🇪 · F. Karsch🇩🇪 · E. Laermann🇩🇪

   We study the free energies of heavy quarks calculated from Polyakov loop correlation functions in full 2-flavour QCD using the p4-improved staggered fermion action. A small but finite Baryon number density is included via Taylor expansion of the fermion determinant in the Baryo-chemical potential mu. For temperatures above Tc we extract Debye screening masses from the large distance behaviour of the free energies and compare their mu-dependence to perturbative results.

   hep-latPoS(2006)·15 citations
8. 08*

   The critical end point of quantum chromodynamics

   Rajiv Gavai🇮🇳 · Sourendu Gupta🇮🇳

   We investigate the critical end point (CEP) of QCD with two flavours of light dynamical quarks at finite lattice cutoff a=1/4T using a Taylor expansion of the baryon number susceptibility. We find a strong volume dependence of the position of the critical end point. In the large volume limit we obtain\ T^E/T_c approximately 0.95 and mu_B^E/T^E approximately 1.1, where T_c is the cross over temperature at zero chemical potential, and T^E and mu_B^E are the temperature and the baryon chemical potential at the critical end point. The small value of mu_B^E places it in the range of observability in energy scans at the RHIC.

   hep-latPoS(2006)·5 citations
9. 09*

   Lattice QCD with light Wilson quarks

   Martin Lüscher🇨🇭

   Wilson's formulation of lattice QCD is attractive for many reasons, but perhaps mainly because of its simplicity and conceptual clarity. Numerical simulations of the Wilson theory (and of its improved versions) tend to be extremely demanding, however, to the extent that they rapidly become impractical at small quark masses. Recent advances in simulation algorithms now allow such simulations to be pushed to significantly smaller masses without having to compromise in other ways. Contact with chiral perturbation theory can thus be made and many physics questions can be addressed that previously appeared to be inaccessible.

   hep-latPoS(2006)·31 citations
10. 10*

    Searching for the critical endpoint in QCD with two quark flavors

    Victor Laliena🇪🇸

    I present a method which can be used to locate the expected critical endpoint of the phase diagram of QCD with two light quark flavors. I illustrate the ideas on a suitable Random Matrix Model and show preliminary results in QCD

    hep-lathep-phPoS(2006)·2 citations
11. 11*

    A (P)HMC algorithm for N_f = 2 + 1 + 1 flavours of twisted mass fermions

    T. Chiarappa🇮🇹 · R. Frezzotti🇮🇹 · C. Urbach🇩🇪

    We present a detailed design of a (P)HMC simulation algorithm for N_f = 2 + 1 + 1 maximally twisted Wilson quark flavours. The algorithm retains even/odd and mass-shift preconditionings combined with multiple Molecular Dynamics time scales for both the light mass degenerate, u and d, quarks and the heavy mass non-degenerate, s and c, quarks. Various non-standard aspects of the algorithm are discussed, among which those connected to the use of a polynomial approximation for the inverse (square root of the squared) Dirac matrix in the s and c quark sector.

    hep-latPoS(2006)·12 citations
12. 12*

    Four quark operators in maximally twisted Wilson LQCD

    Roberto Frezzotti (INFN-Milano and Università di Milano ``Bicocca'')🇮🇹 · Giancarlo Rossi (Università di Roma ``Tor Vergata''and INFN-Roma2)🇮🇹

    We discuss how the peculiar properties of maximally twisted Wilson fermions can be exploited to set up a consistent LQCD computational scheme in which the CP-conserving matrix elements of the $\Delta S=1,2$ effective weak Hamiltonian can be evaluated without mixing with wrong-chirality and/or -parity operators. The proposed lattice framework guarantees automatic O($a$) improvement and positive determinant also for pairs of non-degenerate quarks.

    hep-latPoS(2006)·4 citations
13. 13*

    Zero density heavy quark SU(2) gauge theory and the Stefan-Boltzmann limit

    Kurt Langfeld🇩🇪 · Norbert Lages🇩🇪 · Hugo Reinhardt🇩🇪

    SU(2) lattice gauge theory is investigated where the traces of the Wilson lines at any lattice point and along each direction is constrained to zero. Hence, each of the lattice configurations possesses a vanishing density of heavy (anti-) quarks. The results are compared with those of pure SU(2) gauge theory which can be interpreted as the grand canonical realization of the heavy quark theory where only the ensemble average of the heavy quark density vanishes. The static quark anti-quark potential of the constrained theory is obtained from (spatially smeared) Wilson loops at zero temperature. We find that the potential coincides with that of pure SU(2) gauge theory (without constraints). Hence, the familiar "running" of the lattice spacing with beta is recovered.

    hep-latPoS(2006)·3 citations
14. 14*

    Four-loop plaquette in 3d with a mass regulator

    C. Torrero🇮🇹 · F. Di Renzo🇮🇹 · V. Miccio🇮🇹 · M. Laine🇩🇪 · Y. Schroder🇩🇪

    The QCD free energy can be studied by dimensional reduction to a three-dimensional (3d) effective theory, whereby non-perturbative lattice simulations become less demanding. To connect to the original QCD a perturbative matching computation is required, which is conventionally carried out in dimensional regularization. Therefore the 3d lattice results need to be converted to this regularization scheme as well. The conversion must be carried up to 4-loop order, where the free energy displays an infrared (IR) singularity. We therefore need a regulator which can be implemented both on the lattice and in the continuum computation. We introduce a mass regulator to perform Numerical Stochastic Perturbation Theory computations. Covariant gauge is fixed in the Faddeev-Popov scheme without introducing any ghost fields.

    hep-latPoS(2006)·4 citations
15. 15*

    Wilson fermions quark bilinears to three loops

    F. Di Renzo🇮🇹 · A. Mantovi🇮🇹 · V. Miccio🇮🇹 · C. Torrero🇮🇹 · L. Scorzato🇩🇪

    Quark currents renormalization constants can in principle be safely computed in lattice perturbation theory. In practice, traditional lattice perturbative computations are quite cumbersome, so that so far only the first loop results were available. By making use of Numerical Stochastic Perturbation Theory we reached three (and with less statistical precision even four) loops, both in quenched and in unquenched theory. Convergence properties of the series can be assessed and omparison with non perturbative results (where available) can be made: high loops computations of renormalization constants can be a valuable tool for lattice QCD.

    hep-latPoS(2006)·10 citations
16. 16*

    A determination of the strange quark mass for unquenched clover fermions using the AWI

    M. Göckeler🇩🇪 · R. Horsley🇬🇧 · A. C. Irving🇬🇧 · D. Pleiter🇩🇪 · P. E. L. Rakow🇬🇧 · G. Schierholz🇩🇪 · H. Stüben🇩🇪 · J. M. Zanotti🇬🇧

    Using the O(a) Symanzik improved action an estimate is given for the strange quark mass for unquenched (nf=2) QCD. The determination is via the axial Ward identity (AWI) and includes a non-perturbative evaluation of the renormalisation constant. Numerical results have been obtained at several lattice spacings, enabling the continuum limit to be taken. Results indicate a value for the strange quark mass (in the MSbar-scheme at a scale of 2GeV) in the range 100 - 130MeV.

    hep-latPoS(2006)·8 citations
17. 17*

    Multicritical behavior in the fully frustrated XY model and related systems

    Martin Hasenbusch🇮🇹 · Andrea Pelissetto🇮🇹 · Ettore Vicari🇮🇹

    We study the phase diagram and critical behavior of the two-dimensional square-lattice fully frustrated XY model (FFXY) and of two related models, a lattice discretization of the Landau-Ginzburg-Wilson Hamiltonian for the critical modes of the FFXY model, and a coupled Ising-XY model. We present a finite-size-scaling analysis of the results of high-precision Monte Carlo simulations on square lattices L x L, up to L=O(10^3). In the FFXY model and in the other models, when the transitions are continuous, there are two very close but separate transitions. There is an Ising chiral transition characterized by the onset of chiral long-range order while spins remain paramagnetic. Then, as temperature decreases, the systems undergo a Kosterlitz-Thouless spin transition to a phase with quasi-long-range order. The FFXY model and the other models in a rather large parameter region show a crossover behavior at the chiral and spin transitions that is universal to some extent. We conjecture that this universal behavior is due to a multicritical point. The numerical data suggest that the relevant multicritical point is a zero-temperature transition. A possible candidate is the O(4) point that controls the low-temperature behavior of the 4-vector model.

    ↳ cond-mat.stat-mechcond-mat.supr-conhep-latJ.Stat.Mech.(2005)·19 citations
18. 18*

    Capacity and Character Expansions: Moment generating function and other exact results for MIMO correlated channels

    Steven H. Simon🇺🇸 · Aris L. Moustakas🇺🇸 · Luca Marinelli🇺🇸

    We apply a promising new method from the field of representations of Lie groups to calculate integrals over unitary groups, which are important for multi-antenna communications. To demonstrate the power and simplicity of this technique, we first re-derive a number of results that have been used recently in the community of wireless information theory, using only a few simple steps. In particular, we derive the joint probability distribution of eigenvalues of the matrix GG*, with G a semicorrelated Gaussian random matrix or a Gaussian random matrix with a non-zero mean (and G* its hermitian conjugate) . These joint probability distribution functions can then be used to calculate the moment generating function of the mutual information for Gaussian channels with multiple antennas on both ends with this probability distribution of their channel matrices G. We then turn to the previously unsolved problem of calculating the moment generating function of the mutual information of MIMO (multiple input-multiple output) channels, which are correlated at both the receiver and the transmitter. From this moment generating function we obtain the ergodic average of the mutual information and study the outage probability. These methods can be applied to a number of other problems. As a particular example, we examine unitary encoded space-time transmission of MIMO systems and we derive the received signal distribution when the channel matrix is correlated at the transmitter end.

    ↳ cs.ITcond-mat.mes-hallcond-mat.stat-mechhep-lat+3IEEE Trans.Info.Theor.(2006)·5 citations
19. 19*

    Hadrons Above T_c

    Tetsuo Hatsuda🇯🇵

    Hadronic modes in the quark-gluon plasma and their spectral properties are discussed on the basis of the lattice QCD data.

    ↳ hep-phhep-latnucl-thInt.J.Mod.Phys.A(2006)·15 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.