Wed·Oct 3, 2007Wednesday·October 3, 2007

1. 01*

   The QCD Equation of State with almost Physical Quark Masses

   M. Cheng🇺🇸 · N. H. Christ🇺🇸 · S. Datta🇮🇳 · J. van der Heide🇩🇪 · C. Jung🇺🇸 · F. Karsch🇺🇸 · O. Kaczmarek🇩🇪 · E. Laermann🇩🇪 · R. D. Mawhinney🇺🇸 · C. Miao🇩🇪 · P. Petreczky🇺🇸 · K. Petrov🇩🇰 and 3 other authors

   We present results on the equation of state in QCD with two light quark flavors and a heavier strange quark. Calculations with improved staggered fermions have been performed on lattices with temporal extent Nt =4 and 6 on a line of constant physics with almost physical quark mass values; the pion mass is about 220 MeV, and the strange quark mass is adjusted to its physical value. High statistics results on large lattices are obtained for bulk thermodynamic observables, i.e. pressure, energy and entropy density, at vanishing quark chemical potential for a wide range of temperatures, 140 MeV < T < 800 MeV. We present a detailed discussion of finite cut-off effects which become particularly significant for temperatures larger than about twice the transition temperature. At these high temperatures we also performed calculations of the trace anomaly on lattices with temporal extent Nt=8. Furthermore, we have performed an extensive analysis of zero temperature observables including the light and strange quark condensates and the static quark potential at zero temperature. These are used to set the temperature scale for thermodynamic observables and to calculate renormalized observables that are sensitive to deconfinement and chiral symmetry restoration and become order parameters in the infinite and zero quark mass limits, respectively.

   hep-latnucl-thPRD(2008)·740 citations
2. 02*

   The impact of localized overlap eigenmodes on RMT measurements and topology

   Anna Hasenfratz🇺🇸 · Roland Hoffmann🇺🇸 · Stefan Schaefer🇩🇪

   The low energy eigenmodes of the continuum QCD Dirac operator are extended, but on the lattice, due to discretization effects, the Dirac operator can have localized eigenmodes. These non-physical modes can introduce strong lattice artifacts for observables that are sensitive to chiral symmetry, especially in mixed action simulations. We study how these lattice artifacts depend on the parameters of the overlap operator and their affect on the distribution on the Dirac eigenmodes and the topological susceptibility.

   hep-latPoS(2007)·0 citations
3. 03*

   What's up with IR gluon and ghost propagators in Landau gauge? A puzzling answer from huge lattices

   Attilio Cucchieri🇧🇷 · Tereza Mendes🇧🇷

   Several analytic approaches predict for SU(N_c) Yang-Mills theories in Landau gauge an enhanced ghost propagator G(p^2) and a suppressed gluon propagator D(p^2) at small momenta. This prediction applies to two, three and four space-time dimensions. Moreover, the gluon propagator is predicted to be null at p = 0. Numerical studies by several groups indeed support an enhanced ghost propagator when compared to the tree-level behavior $1/p^2$ and a finite infrared gluon propagator. However, the agreement between analytic and numerical studies is only at the qualitative level in three and in four dimensions. In particular, the infrared exponent of the ghost propagator seems to be smaller than the one predicted analytically and the gluon propagator seems to display a (finite) nonzero value at zero momentum. It has been argued that this discrepancy might go away once simulations are done on much larger lattice sizes than the ones used up to now. Here we present data in three and four space-time dimensions using huge lattices in the scaling region, i.e. up to 320^3 at beta = 3.0 and up to 128^4 at beta = 2.2, corresponding to V \approx (85 fm)^3 and V \approx (27 fm)^4. Simulations have been done on the IBM supercomputer at the University of Sao Paulo

   hep-latPoS(2007)·422 citations
4. 04*

   Chiral behaviour of Delta B = 2 and Delta C =2 matrix elements

   William Detmold🇺🇸 · C.-J. David Lin🇹🇼

   We investigate the light-quark mass and spatial volume dependence of matrix elements of Delta B = 2 and Delta C = 2 four-fermion operators. These operators are relevant for Neutral B(s) and D mixing in and beyond the Standard Model. An important conclusion of this work is that the chiral extrapolations for matrix elements of heavy-light meson mixing beyond the Standard Model are more complicated than that for the Standard Model mixing matrix elements.

   hep-latPoS(2007)·0 citations
5. 05*

   Nucleon form factors and structure functions with N_f=2+1 dynamical domain wall fermions

   RBC-UKQCD Collaborations: Takeshi Yamazaki🇺🇸 · Shigemi Ohta🇯🇵

   We report isovector form factors and low moments of structure functions of nucleon in numerical lattice quantum chromodynamics (QCD) from the on-going calculations by the RIKEN-BNL-Columbia (RBC) and UKQCD Collaborations with (2+1) dynamical flavors of domain-wall fermion (DWF) quarks. We calculate the matrix elements with four light quark masses, corresponding to pion mass values of m_\pi = 330-670 MeV, while the dynamical strange mass is fixed at a value close to physical, on (2.7 fm)^3 spatial volume. We found that our axial charge, g_A, at the lightest mass exhibits a large deviation from the heavier mass results. This deviation seems to be a finite-size effect as the g_A value scales with a single parameter, m_\pi L, the product of pion mass and linear spatial lattice size. The scaling is also seen in earlier 2-flavor dynamical DWF and Wilson quark calculations. Without this lightest point, the three heavier mass results show only very mild mass dependence and linearly extrapolate to g_A=1.16(6). We determined the four form factors, the vector (Dirac), induced tensor (Pauli), axial vector and induced pseudoscalar, at a few finite momentum transfer values as well. At the physical pion mass the form-factors root mean square radii determined from the momentum-transfer dependence %of the form factors are 20-30% smaller than the corresonding experiments. The ratio of the isovector quark momentum to helicity fractions, < x>_{u-d}/< x>_{\Delta u - \Delta d} is in agreement with experiment without much mass dependence including the lightest point. We obtain an estimate, 0.81(2), by a constant fit. Although the individual momentum and helicity fractions are yet to be renormalized, they show encouraging trend toward experiment.

   hep-latPoS(2007)·14 citations
6. 06*

   Oscillatory terms in the domain wall transfer matrix

   Sergey Syritsyn🇺🇸 · John W. Negele🇺🇸

   We study the transfer matrix for domain wall fermions to understand the origin and significance of oscillatory contributions to hadron correlation functions that arise for M >1. For a free particle in one space, one time, and one flavor dimension, the eigenmodes of the one-body operator appearing in the transfer matrix are calculated, and the role of the negative eigenmodes arising when M > 1 is studied. In the case of three space dimensions, oscillatory behavior for hadron correlation functions in QCD is shown to emerge for free fermions when M exceeds 1, and to increase with increasing M. Analogous behavior is observed for domain wall fermions on HYP smeared MILC lattices, and a procedure is demonstrated for subtracting oscillating terms from physical observables.

   hep-latPoS(2007)·18 citations
7. 07*

   I=2 Two-Pion Wave Functions with Non-zero Total Momentum

   Kiyoshi Sasaki🇯🇵 · Naruhito Ishizuka (Univ. of Tsukuba)🇯🇵

   We calculate the two-pion wave function for the I=2 $S$-wave two-pion system with a finite scattering momentum and estimate the interaction range between two pions. It allows us to examine the validity of the necessary condition for the finite-volume method for the scattering phase shift. A calculation is carried out with a plaquette gauge action for gluons and a clover-improved Wilson action for quarks at $1/a=1.63\mathrm{GeV}$ on $32^3\times 120$ lattice in the quenched approximation. We conclude that the necessary condition is satisfied within statistical errors for the lattice size $L\ge 32$, when the quark mass is in the range $m_{\pi }^2=0.176-0.345{\mathrm{GeV}}^2$ and the scattering momentum in $k^2<0.026{\mathrm{GeV}}^2$. We also find that the energy dependence of the interaction range is small and it takes $1.2-1.7\mathrm{fm}$ for our simulation parameters. We obtain the phase shift from the two-pion wave function with a smaller statistical error than that from the conventional analysis with the two-pion time correlator.

   hep-latPoS(2007)·3 citations
8. 08*

   A Lattice Formulation of Two Dimensional Topological Field Theory

   Kazutoshi Ohta🇯🇵 · Tomohisa Takimi🇯🇵

   We propose a non-perturbative criterion to investigate whether supersymmetric lattice gauge theories preserving partial SUSY can have the desired continuum limit or not. Since the target continuum theories of the lattice models are extended supersymmetric gauge theories including the topological field theory (TFT) as a special subsector, the continuum limits of them should reproduce the properties of the TFT. Therefore, whether the property of the TFT can be recovered at the continuum limit becomes a non-perturbative criterion. Then we accept it as a criterion. In this paper, among the topological properties, we investigate the BRST cohomology on the two dimensional $\mathcal{N}=(4,4)$ CKKU lattice model without moduli fixing mass term. We show that the BRST cohomology in the target continuum theory cannot be realized from the BRST cohomology on the lattice. From this result, we obtain the possible implication that the $\mathcal{N}=(4,4)$ CKKU model cannot recover the target continuum theory if the non-perturbative effects are taken into account.

   hep-latPoS(2007)·1 citation
9. 09*

   B_K with dynamical overlap fermions

   JLQCD Collaboration: N. Yamada🇯🇵 · S. Aoki🇯🇵 · H. Fukaya🇯🇵 · S. Hashimoto🇯🇵 · J. Noaki🇯🇵 · T. Kaneko🇯🇵 · H. Matsufuru🇯🇵 · T. Onogi🇯🇵

   We report on a calculation of $B_K$ with two-flavor dynamical overlap fermions on a $16^3\times 32$ lattice at $a\sim 0.12$ fm. The results are compared with the PQChPT prediction of quark mass dependence. The systematic errors due to finite volume effects and fixing topology are discussed.

   hep-latPoS(2007)·6 citations
10. 10*

    Non-perturbative improvement of nHYP smeared Wilson fermions

    Roland Hoffmann🇺🇸 · Anna Hasenfratz🇺🇸 · Stefan Schaefer🇩🇪

    Using Schroedinger functional techniques, we determine the coefficient of the clover term necessary for non-perturbative O(a) improvement of hypercubic smeared Wilson fermions on a quenched plaquette action background. Unlike for unsmeared Wilson fermions, the resulting clover coefficients are close to the tree-level value even at coarse lattice spacings, indicating the absence of large cutoff effects. A number of exploratory tests are also performed with the improved action.

    hep-latPoS(2007)·24 citations
11. 11*

    Vortex topology and the continuum limit of lattice gauge theories

    G. Burgio🇩🇪

    We study the stability of Z_2 topological vortex excitations in d+1 dimensional SU(2) Yang-Mills theory on the lattice at T=0. This is found to depend on d and on the coupling considered. We discuss the connection with lattice artifacts causing bulk transitions in the beta_A-beta_F plane and draw some conclusions regarding the continuum limit of the theory.

    hep-latPoS(2007)·5 citations
12. 12*

    Smearing and filtering methods in lattice QCD - a quantitative comparison

    Stefan Solbrig🇩🇪 · Falk Bruckmann🇩🇪 · Christof Gattringer🇦🇹 · Ernst-Michael Ilgenfritz🇩🇪 · Michael Müller-Preussker🇩🇪 · Andreas Schäfer🇩🇪

    We systematically compare three filtering methods used to extract topological excitations from lattice gauge configurations, namely smearing, Laplace filtering and the filtered fermionic topological charge (with chirally improved fermions). Each of these techniques introduces ambiguities, like its parameter dependence. We show, however, that all these methods can be tuned to each other over a broad range of filtering levels and that they reveal very similar topological structures. For these common structures we find an interesting power-law relating the number and packing fraction of clusters of filtered topological charge.

    hep-latPoS(2007)·8 citations
13. 13*

    Confinement: $G_2$ group case

    Guido Cossu🇮🇹 · Massimo D'Elia🇮🇹 · Adriano Di Giacomo🇮🇹 · Biagio Lucini🇬🇧 · Claudio Pica🇺🇸

    The gauge group being centreless, $G_2$ gauge theory is a good laboratory for studying the role of the centre of the group for colour confinement in Yang-Mills gauge theories. In this paper, we investigate $G_2$ pure gauge theory at finite temperature on the lattice. By studying the finite size scaling of the plaquette, the Polyakov loop and their susceptibilities, we show that a deconfinement phase transition takes place. The analysis of the pseudocritical exponents give strong evidence of the deconfinement transition being first order. Implications of our findings for scenarios of colour confinement are discussed.

    hep-latPoS(2007)·12 citations
14. 14*

    Lattice supersymmetry in 1D with two supercharges

    S. Arianos🇮🇹 · A. D'Adda🇮🇹 · N. Kawamoto🇯🇵 · J. Saito🇯🇵

    A consistent formulation of a fully supersymmetric theory on the lattice has been a long standing challenge. In recent years there has been a renewed interest on this problem with different approaches. At the basis of the formulation we present in the following there is the Dirac-Kahler twisting procedure, which was proposed in the continuum for a number of theories, including N=4 SUSY in four dimensions. Following the formalism developed in recent papers, an exact supersymmetric theory with two supercharges on a one dimensional lattice is realized using a matrix-based model. The matrix structure is obtained from the shift and clock matrices used in two dimensional non-commutative field theories. The matrix structure reproduces on a one dimensional lattice the expected modified Leibniz rule. Recent claims of inconsistency of the formalism are discussed and shown not to be relevant.

    hep-latPoS(2007)·15 citations
15. 15*

    On the ratio of string tensions in the 3D Z_4 lattice gauge theory

    M. Caselle🇮🇹 · P. Giudice🇮🇹 · F. Gliozzi🇮🇹 · P. Grinza🇮🇹 · S. Lottini🇮🇹

    It was recently pointed out that simple scaling properties of Polyakov correlation functions of gauge systems in the confining phase suggest that the ratios of k-string tensions in the low temperature region is constant up to terms of order T^3. Here we argue that, at least in a three-dimensional Z_4 gauge model, the above ratios are constant in the whole confining phase. This result is obtained by combining numerical experiments with known exact results on the mass spectrum of an integrable two-dimensional spin model describing the infrared behaviour of the gauge system near the deconfining transition.

    hep-lathep-thPoS(2007)·2 citations
16. 16*

    P- and D-wave spin-orbit splittings in heavy-light mesons

    J. Koponen🇫🇮

    This is a summary of a detailed study of heavy-light meson excited state energies. Our lattice measurements include both radial and orbital excitations. Particular attention is paid to the spin-orbit splittings, to see which one of the states (for a given angular momentum L) has the lower energy. In nature the closest equivalent of this heavy-light system is the B_s meson, which allows us to compare our lattice calculations to experimental results (where available) or give a prediction where the excited states, particularly P-wave states, should lie.

    hep-latPoS(2007)·1 citation
17. 17*

    Screening at finite temperature and density

    O.Kaczmarek🇩🇪

    We present lattice QCD results on heavy quark free energies, extract from its temperature dependence entropy and internal energy contributions, and discuss the onset of medium effects that lead to screening of static quark-antiquark sources in a thermal medium. Most results are obtained in (2+1)-flavour QCD on a line of constant physics with almost realistic quark masses and compared to previous results from 2-flavor QCD as well as pure gauge theory. Furthermore, we discuss results on the density dependence of screening masses that have been obtained using a leading order Taylor expansion in the baryon chemical potential.

    hep-lathep-phPoS(2007)·62 citations
18. 18*

    Wilson Loop in Classical Lattice Gauge Theory and the Thermal Width of Heavy Quarkonium

    M. Laine🇩🇪 · O. Philipsen🇩🇪 · M. Tassler🇩🇪

    We present an estimate for the imaginary part of the recently introduced finite temperature real-time static potential. It can be extracted from the time evolution of the Wilson loop in classical lattice gauge theory. The real-time static potential determines, through a Schroedinger-type equation and a subsequent Fourier-transform of its solution, the spectral function of heavy quarkonium in finite-temperature QCD. We also compare the results of the classical simulations with those of Hard Thermal Loop improved simulations, as well as with analytic expectations based on resummed perturbation theory.

    hep-latPoS(2007)·5 citations
19. 19*

    Strong coupling expansion for Yang-Mills theory at finite temperature

    J. Langelage🇩🇪 · G. Münster🇩🇪 · O. Philipsen🇩🇪

    Euclidean strong coupling expansion of the partition function is applied to lattice Yang-Mills theory at finite temperature, i.e. for lattices with a compactified temporal direction. The expansions have a finite radius of convergence and thus are valid only for $\beta <{\beta }_c$, where ${\beta }_c$ denotes the nearest singularity of the free energy on the real axis. The accessible temperature range is thus the confined regime up to the deconfinement transition. We have calculated the first few orders of these expansions of the free energy density as well as the screening masses for the gauge groups SU(2) and SU(3). The resulting free energy series can be summed up and corresponds to a glueball gas of the lowest mass glueballs up to the calculated order. Our result can be used to fix the lower integration constant for Monte Carlo calculations of the thermodynamic pressure via the integral method, and shows from first principles that in the confined phase this constant is indeed exponentially small. Similarly, our results also explain the weak temperature dependence of glueball screening masses below $T_c$, as observed in Monte Carlo simulations. Possibilities and difficulties in extracting ${\beta }_c$ from the series are discussed.

    hep-latPoS(2007)·3 citations
20. 20*

    Chiral Limit and Light Quark Masses in 2+1 Flavor Domain Wall QCD

    RBC-UKQCD Collaboration: M. F. Lin🇺🇸 · E. E. Scholz🇺🇸

    We present results for meson masses and decay constants measured on 24^3x64 lattices using the domain wall fermion formulation with an extension of the fifth dimension of L_s=16 for N_f=2+1 dynamical quark flavors. The lightest dynamical meson mass in our set-up is around 331 MeV, while partially quenched mesons reach masses as low as 250 MeV. The applicability of SU(3)xSU(3) and SU(2)xSU(2) (partially quenched) chiral perturbation theory will be compared and we quote values for the low-energy constants from both approaches. We will extract the average light quark and strange quark masses and use a non-perturbative renormalization technique (RI/MOM) to quote their physical values. The pion and kaon decay constants are determined at those values from our chiral fits and their ratio is used to obtain the CKM-matrix element |V_us|. The results presented here include statistical errors only.

    hep-latPoS(2007)·18 citations
21. 21*

    Chiral Analysis of the Generalized Form Factors of the Nucleon

    Marina Dorati🇮🇹 · Tobias A. Gail🇩🇪 · Thomas R. Hemmert🇩🇪

    We apply the methods of Chiral Perturbation Theory to the analysis of the first moments of the Generalized Parton Distributions in a Nucleon, usually known as generalized form factors. These quantities are currently also under investigation in Lattice QCD analyses of baryon structure, providing simulation results at large quark masses to be extrapolated to the "real world" via Chiral Effective Field Theory. We have performed a leading-one-loop calculation in the covariant framework of Baryon Chiral Perturbation Theory (BChPT), predicting both the momentum and the quark-mass dependence for all the vector and axial (generalized) form factors. In particular we discuss the results for the limit of vanishing four-momentum transfer where the GPD-moments reduce to the well known moments of Parton Distribution Functions (PDFs). We fit our results to available lattice QCD data, extrapolating down to the physical point. We conclude by presenting outstanding results from a combined fit to different GPDs-moments.

    hep-lathep-phnucl-thPoS(2007)·7 citations
22. 22*

    Coulomb gauge Green functions and Gribov copies in SU(2) lattice gauge theory

    M. Quandt🇩🇪 · G. Burgio🇩🇪 · S. Chimchinda🇩🇪 · H. Reinhardt🇩🇪

    We reconsider the lattice measurement of Green functions in Coulomb gauge, both in 2+1 and 3+1 dimensions, using an improved gauge fixing scheme. The influence of Gribov copies is examined and we find clear indications that Green functions are more strongly affected than previously assumed, in particular for low momenta. Qualitatively, our improved lattice results in the infra-red compare more favourably with recent continuum calculations in the Hamiltonian approach.

    hep-latPoS(2007)·20 citations
23. 23*

    2+1 flavor QCD with the fixed point action in the $ϵ$-regime

    Peter Hasenfratz🇨🇭 · Dieter Hierl🇩🇪 · Vidushi Maillart🇨🇭 · Ferenc Niedermayer🇨🇭 · Andreas Schafer🇩🇪 · Christof Weiermann🇨🇭 · Manuel Weingart🇨🇭

    We generated configurations with the approximate fixed-point Dirac operator $D_{\mathrm{FP}}$ on a $12^4$ lattice with $a\approx 0.13$fm where the scale was set by $r_0$. The distributions of the low lying eigenvalues in different topological sectors were compared with those of the Random Matrix Theory which leads to a prediction of the chiral condensate.

    hep-latPoS(2007)·9 citations
24. 24*

    High loop renormalization constants by NSPT: a status report

    Francesco Di Renzo🇮🇹 · Luigi Scorzato🇮🇹 · Christian Torrero🇩🇪

    We present an update on Numerical Stochastic Perturbation Theory projects for Lattice QCD, which are by now run on apeNEXT. As a first issue, we discuss a strategy to tackle finite size effects which can be quite sizeable in the computation of logarithmically divergent renormalization constants. Our first high loop determination of quark bilinears for Wilson fermions was limited to finite constants and finite ratios. A precise determination of Z_P and Z_S (and hence of Z_m) now becomes possible. We also give an account of computations for actions different from the standard regularization we have taken into account so far (Wilson gauge action and Wilson fermions). In particular, we present the status of computations for the Lattice QCD regularization defined by tree level Symanzik improved gauge action and Wilson fermions, which became quite popular in recent times. We also take the chance to discuss the related topic of the computation of the gluon and ghost propagators (which we undertook in collaboration with another group). This is relevant in order to better understand non-perturbative computations of propagators aiming at qualitative/quantitative understanding of confinement.

    hep-latPoS(2007)·7 citations
25. 25*

    The lattice gluon propagator in stochastic perturbation theory

    E.-M.Ilgenfritz🇩🇪 · H. Perlt🇩🇪 · A. Schiller🇩🇪

    We calculate loop contributions up to four loops to the Landau gauge gluon propagator in numerical stochastic perturbation theory. For different lattice volumes we carefully extrapolate the Euler time step to zero for the Langevin dynamics derived from the Wilson action. The one-loop result for the gluon propagator is compared to the infinite volume limit of standard lattice perturbation theory.

    hep-latPoS(2007)·7 citations
26. 26*

    Twisted mass QCD at finite temperature

    E.-M. Ilgenfritz🇩🇪 · M. Müller-Preußker🇩🇪 · M. Petschlies (HU Berlin)🇩🇪 · K. Jansen (DESY Zeuthen)🇩🇪 · M.P. Lombardo (INFN Frascati)🇮🇹 · O. Philipsen🇩🇪 · L. Zeidlewicz (U Münster)🇩🇪 · A. Sternbeck (U Adelaide)🇦🇺

    We discuss the use of Wilson fermions with twisted mass for simulations of QCD thermodynamics. As a prerequisite for a future analysis of the finite-temperature transition making use of automatic O(a) improvement, we investigate the phase structure in the space spanned by the hopping parameter kappa, the coupling beta, and the twisted mass parameter mu. We present results for N_f=2 degenerate quarks on a 16^3x8 lattice, for which we investigate the possibility of an Aoki phase existing at strong coupling and vanishing mu, as well as of a thermal phase transition at moderate gauge couplings and non-vanishing mu.

    hep-latPoS(2007)·5 citations
27. 27*

    The B-meson mass splitting from non-perturbative quenched lattice QCD

    A.G. Grozin🇷🇺 · D. Guazzini🇩🇪 · P. Marquard🇩🇪 · H.B. Meyer🇺🇸 · J.H. Piclum🇨🇦 · R. Sommer🇩🇪 · M. Steinhauser🇩🇪

    We perform the non-perturbative (quenched) renormalization of the chromo-magnetic operator in Heavy Quark Effective Theory and its three-loop matching to QCD. At order 1/m of the expansion, the operator is responsible for the mass splitting between the pseudoscalar and vector B-mesons. These new computed factors are affected by an uncertainty negligible in comparison to the known bare matrix element of the operator between B-states. Furthermore, they push the quenched determination of the spin splitting for the Bs-meson much closer to its experimental value than the previous perturbatively renormalized computations. The renormalization factor for three commonly used heavy quark actions and the Wilson gauge action and useful parametrizations of the matching coefficient are provided.

    hep-lathep-phPoS(2007)·2 citations
28. 28*

    Primordial magnetic fields at preheating

    A. Diaz-Gil🇪🇸 · J. Garcia-Bellido🇪🇸 · M. Garcia Perez🇪🇸 · A. Gonzalez-Arroyo🇪🇸

    Using lattice techniques we investigate the generation of long range cosmological magnetic fields during a cold electroweak transition. We will show how magnetic fields arise, during bubble collisions, in the form of magnetic strings. We conjecture that these magnetic strings originate from the alignment of magnetic dipoles associated with EW sphaleron-like configurations. We also discuss the early thermalisation of photons and the turbulent behaviour of the scalar fields after tachyonic preheating.

    hep-latastro-phhep-phPoS(2007)·14 citations
29. 29*

    Taste violations in the scalar correlator in mixed action simulations

    C. Aubin🇺🇸 · Jack Laiho🇺🇸 · Ruth S. Van de Water🇺🇸

    We study the behavior of the isovector scalar correlator, which is particularly sensitive to lattice artifacts, using domain-wall valence quarks on a staggered sea (generated by the MILC collaboration). We analyze this according to the prediction from chiral perturbation theory determined by Prelovsek, which indicates that the leading unitarity violations come from taste breaking effects. We show that our data behaves in the way predicted by Prelovsek, thus verifying that the largest contribution to the violations of unitarity which arise at finite lattice spacing can be described by the mixed-action chiral perturbation theory.

    hep-latPoS(2007)·5 citations
30. 30*

    Equivalence of QCD in the epsilon-regime and chiral Random Matrix Theory with or without chemical potential

    Francesco Basile🇬🇧 · Gernot Akemann🇬🇧

    We prove that QCD in the epsilon-regime of chiral Perturbation Theory is equivalent to chiral Random Matrix Theory for zero and both non-zero real and imaginary chemical potential mu. To this aim we prove a theorem that relates integrals over fermionic and bosonic variables to super-Hermitian or super-Unitary groups also called superbosonization. Our findings extend previous results for the equivalence of the partition functions, spectral densities and the quenched two-point densities. We can show that all k-point density correlation functions agree in both theories for an arbitrary number of quark flavors, for either mu=0 or mu=/=0 taking real or imaginary values. This implies the equivalence for all individual k-th eigenvalue distributions which are particularly useful to determine low energy constants from Lattice QCD with chiral fermions.

    ↳ hep-thhep-latmath-phmath.MPJHEP(2007)·55 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.