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Sep 21, 2013
09/13

by
C. E. DeTar; U. M. Heller

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We review the current methods and results of lattice simulations of quantum chromodynamics at nonzero temperatures and densities. The review is intended to introduce the subject to interested nonspecialists and beginners. It includes a brief overview of lattice gauge theory, a discussion of the determination of the crossover temperature, the QCD phase diagram at zero and nonzero densities, the equation of state, some in-medium properties of hadrons including charmonium, and some plasma...

Source: http://arxiv.org/abs/0905.2949v3

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Sep 18, 2013
09/13

by
R. G. Edwards; U. M. Heller

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We show how the standard domain wall action can be simply modified to allow arbitrarily exact chiral symmetry at finite fifth dimensional extent. We note that the method can be used for both quenched and dynamical calculations. We test the method using smooth and thermalized gauge field configurations. We also make comparisons of the performance (cost) of the domain wall operator for spectroscopy compared to other methods such as the overlap-Dirac operator and find both methods are comparable...

Source: http://arxiv.org/abs/hep-lat/0005002v1

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Sep 20, 2013
09/13

by
J. Fingberg; U. M. Heller; F. Karsch

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We determine the critical couplings for the deconfinement phase transition in $SU(2)$ gauge theory on $N_\tau \times N_\sigma^3$ lattices with $N_\tau = 8$ and 16 and $N_\sigma$ varying between 16 and 48. A comparison with string tension data shows scaling of the ratio $T_c / \sqrt{\sigma}$ in the entire coupling regime $\beta =2.30-2.75$, while the individual quantities still exhibit large scaling violations. We find $T_c / \sqrt{\sigma}=0.69(2)$. We also discuss in detail the extrapolation of...

Source: http://arxiv.org/abs/hep-lat/9208012v2

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Sep 22, 2013
09/13

by
U. M. Heller; F. Karsch; J. Rank

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We discuss the calculation of electric and magnetic screening masses in SU(2) gauge theory. The temperature dependence of these masses obtained from the long-distance behaviour of spatial correlation functions has been analyzed for temperatures up to 10000 T_c.

Source: http://arxiv.org/abs/hep-lat/9708009v1

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Sep 19, 2013
09/13

by
U. M. Heller; F. Karsch; J. Rank

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From the long-distance behaviour of gluon and Polyakov loop correlation functions we extract masses resp. energies in the electric and magnetic sectors. We discuss their dependence on the temperature and on the momentum as well as the relevance of an improvement of the lattice discretization of the action.

Source: http://arxiv.org/abs/hep-lat/9709065v1

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Sep 18, 2013
09/13

by
U. M. Heller; F. Karsch; J. Rank

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We study the gluon propagator and the singlet potential in Landau gauge in the deconfined phase of SU(2) lattice gauge theory, using both the standard Wilson action and a tree-level Symanzik improved action. From the long-distance behavior of correlation functions of temporal and spatial components of the gauge fields we extract electric (m_e) and magnetic (m_m) screening masses. For the magnetic mass we find m_m(T) = 0.456(6) g^2(T) T. The electric mass can be described by a next-to leading...

Source: http://arxiv.org/abs/hep-lat/9710033v1

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Sep 18, 2013
09/13

by
U. M. Heller; F. Karsch; B. Sturm

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We analyze the cut-off dependence of the fermion contribution to the finite temperature free energy density in ${\cal O}(g^2)$ lattice perturbation theory for several improved staggered fermion actions. Cut-off effects are drastically reduced for the Naik action and an action with improved rotational symmetry of the quark propagator. We show that improvement of rotational symmetry at ${\cal O}(g^2)$ further reduces cut-off effects in thermodynamic observables. We also show that the introduction...

Source: http://arxiv.org/abs/hep-lat/9901010v1

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Sep 18, 2013
09/13

by
U. M. Heller; H. Neuberger; P. Vranas

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Lattice work, exploring the Higgs mass triviality bound, seems to indicate that a strongly interacting scalar sector in the minimal standard model cannot exist while low energy QCD phenomenology seems to indicate that it could. We attack this puzzle using the 1/N expansion and discover a simple criterion for selecting a lattice action that is more likely to produce a heavy Higgs particle. Our large $N$ calculation suggests that the Higgs mass bound might be around $850 GeV$, which is about 30%...

Source: http://arxiv.org/abs/hep-lat/9107001v1

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Jul 20, 2013
07/13

by
J. Fingberg; U. M. Heller; V. Mitrjushkin

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We investigate universality, scaling, the beta-function and the topological charge in the positive plaquette model for SU(2) lattice gauge theory. Comparing physical quantities, like the critical temperature, the string tension, glueball masses, and their ratios, we explore the effect of a complete suppression of a certain lattice artifact, namely the negative plaquettes, for SU(2) lattice gauge theory. Our result is that this modification does not change the continuum limit, i.e., the...

Source: http://arxiv.org/abs/hep-lat/9407011v1

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Sep 23, 2013
09/13

by
R. Höllwieser; M. Faber; U. M. Heller

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We analyze topological charge contributions from classical SU(2) center vortices with shapes of planes and spheres using different topological charge definitions, namely the center vortex picture of topological charge, a discrete version of F\~{F} in the plaquette and hypercube definitions and the lattice index theorem. For the latter the zeromodes of the Dirac operator in the fundamental and adjoint representations using both the overlap and asqtad staggered fermion formulations are...

Source: http://arxiv.org/abs/1202.0929v3

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Sep 22, 2013
09/13

by
R. G. Edwards; U. M. Heller; R. Narayanan

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We review the spectral flow techniques for computing the index of the overlap Dirac operator including results relevant for SUSY Yang-Mills theories. We describe properties of the overlap Dirac operator, and methods to implement it numerically. We use the results from the spectral flow to illuminate the difficulties in numerical calculations involving domain wall and overlap fermions.

Source: http://arxiv.org/abs/hep-lat/0001013v1

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Sep 23, 2013
09/13

by
P. H. Damgaard; U. M. Heller; K. Splittorff

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The microscopic spectral density of the Hermitian Wilson-Dirac operator is computed numerically in quenched lattice QCD. We demonstrate that the results given for fixed index of the Wilson-Dirac operator can be matched by the predictions from Wilson chiral perturbation theory. We test successfully the finite volume and the mass scaling predicted by Wilson chiral perturbation theory at fixed lattice spacing.

Source: http://arxiv.org/abs/1110.2851v2

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Sep 20, 2013
09/13

by
P. H. Damgaard; U. M. Heller; A. Krasnitz

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Measurements of the lowest-lying eigenvalues of the staggered fermion Dirac operator are made on ensembles of equilibrium gauge field configurations in quenched SU(3) lattice gauge theory. The results are compared with exact analytical predictions in the microscopic finite-volume scaling regime.

Source: http://arxiv.org/abs/hep-lat/9810060v1

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Sep 21, 2013
09/13

by
P. O. Bowman; U. M. Heller; A. G. Williams

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We report on the lattice quark propagator using standard and improved Staggered quark actions, with the standard, Wilson gauge action. The standard Kogut-Susskind action has errors of \oa{2} while the ``Asqtad'' action has \oa{4}, \oag{2}{2} errors. The quark propagator is interesting for studying the phenomenon of dynamical chiral symmetry breaking and as a test-bed for improvement. Gauge dependent quantities from lattice simulations may be affected by Gribov copies. We explore this by...

Source: http://arxiv.org/abs/hep-lat/0203001v1

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Sep 19, 2013
09/13

by
U M. Heller; M. Klomfass; H. Neuberger; P. Vranas

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Previous large $N$ calculations are combined with numerical work at $N=4$ to show that the Minimal Standard Model will describe physics to an accuracy of a few percent up to energies of the order 2 to 4 times the Higgs mass, $M_H$, only if $M_H \le 710\pm60 ~ GeV$. This bound is the result of a systematic search in the space of dimension six operators and is expected to hold in the {\it continuum}. Given that studying the scalar sector in isolation is already an approximation, we believe that...

Source: http://arxiv.org/abs/hep-ph/9303215v1

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Sep 21, 2013
09/13

by
R. G. Edwards; U. M. Heller; T. R. Klassen

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The ALPHA collaboration has determined the O(a) improved Wilson quark action for lattice spacings $a\leq 0.1$ fm, in the quenched approximation. We extend this result to coarser lattices, $a\leq 0.17$ fm, and calculate the hadron spectrum on them. The large range of lattice spacings obtained by combining our results with earlier ones on finer lattices, allow us to present a convincing demonstration of the efficiency of non-perturbative O(a) improvement. We find that scaling violations of the...

Source: http://arxiv.org/abs/hep-lat/9711052v2

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Sep 23, 2013
09/13

by
H. Ohno; U. M. Heller; F. Karsch; S. Mukherjee

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We report on the behavior of the eigenvalue distribution of the Dirac operator in (2+1)-flavor QCD at finite temperature, using the HISQ action. We calculate the eigenvalue density at several values of the temperature close to the pseudocritical temperature. For this study we use gauge field configurations generated on lattices of size $32^3 \times 8$ with two light quark masses corresponding to pion masses of about 160 and 115 MeV. We find that the eigenvalue density below $T_c$ receives large...

Source: http://arxiv.org/abs/1111.1939v1

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Sep 18, 2013
09/13

by
P. O. Bowman; U. M. Heller; A. G. Williams

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We present results for the lattice quark propagator in both Landau and Laplacian gauges using standard and improved staggered quark actions. The standard Kogut-Susskind action has errors of \oa{2} while the improved ``Asqtad'' action has \oa{4}, \oag{2}{2} errors. This improvement is seen in the quark propagator. We demonstrate the application of tree-level corrections to these actions and see that Landau and Laplacian gauges produce very similar results.

Source: http://arxiv.org/abs/hep-lat/0110081v1

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Sep 21, 2013
09/13

by
R. G. Edwards; U. M. Heller; T. R. Klassen

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Accurate determinations of the physical scale of a lattice action are required to check scaling and take the continuum limit. We present a high statistics study of the static potential for the SU(3) Wilson gauge action on coarse lattices ($5.54 \leq \beta \leq 6.0$). Using an improved analysis procedure we determine the string tension and the Sommer scale $r_0$ (and related quantities) to 1% accuracy, including all systematic errors. Combining our results with earlier ones on finer lattices, we...

Source: http://arxiv.org/abs/hep-lat/9711003v2

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Sep 20, 2013
09/13

by
H. Neuberger; U. M. Heller; M. Klomfass; P. Vranas

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Older lattice work exploring the Higgs mass triviality bound is briefly reviewed. It indicates that a strongly interacting scalar sector in the minimal standard model cannot exist; on the other hand low energy QCD phenomenology might be interpreted as an indication that it could. We attack this puzzle using the $1/N$ expansion and discover a simple criterion for selecting a lattice action that is more likely to produce a heavy Higgs particle. Depending on the precise form of the limitation put...

Source: http://arxiv.org/abs/hep-lat/9208017v1

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Sep 19, 2013
09/13

by
B. Grossman; Sourendu Gupta; U. M. Heller; F. Karsch

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We investigate the finite-temperature excitation spectrum in the gluon sector of $SU(3)$ pure gauge theory through measurements of screening masses in correlations of loop operators. We develop the classification of such operators under the symmetry group of the `$z$-slice'. In the confined phase of the theory, we find that the spectrum dynamically realises the zero temperature symmetries. We observe a large thermal shift of the $0^{++}$ glueball mass. In the deconfined phase, the spectrum...

Source: http://arxiv.org/abs/hep-lat/9309007v1

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Sep 19, 2013
09/13

by
M. Wingate; T. DeGrand; S. Collins; U. M. Heller

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In this work we present lattice calculations of the masses of P-wave mesons using Monte Carlo simulations. Our valence fermions are defined by the Wilson action. Our gauge fields are generated with both dynamical staggered fermions at a lattice coupling $\beta\equiv 6/g^2=5.6$ for sea quark masses of $am_q=0.010$ and 0.025, and in the quenched approximation at $\beta=6.0$. We present results for charm and charmonium spectroscopy and use them to compute the strong coupling constant $\alpha_s$....

Source: http://arxiv.org/abs/hep-lat/9501034v1

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Sep 18, 2013
09/13

by
R. G. Edwards; U. M. Heller; T. R. Klassen

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After describing the Schr\"odinger functional for standard and improved gluon and quark actions we present results for the non-perturbative clover coefficients of the SW quark action coupled to the Wilson plaquette action for $\beta \geq 5.7$, as well as the L\"uscher-Weisz one-loop tadpole improved gauge action, both in the quenched approximation.

Source: http://arxiv.org/abs/hep-lat/9710054v1

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Sep 18, 2013
09/13

by
H. Ohno; U. M. Heller; F. Karsch; S. Mukherjee

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We investigate $U_A(1)$ breaking above $T_c$ in terms of the Dirac spectrum on configurations with (2+1)-flavors, using the HISQ action. The strange quark mass is at its physical value. We use several light quark masses corresponding to the Goldstone pion masses in the range of about 115 -- 230 MeV on lattices of size 32$^3 \times$8 and 48$^3 \times$8. We calculate the 100 lowest-lying Dirac eigenvalues at temperatures below and above $T_c$. We investigate the volume dependence of the Dirac...

Source: http://arxiv.org/abs/1211.2591v1

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Sep 20, 2013
09/13

by
Sara Collins; R. G. Edwards; U. M. Heller; John Sloan

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The improved Wilson quark action - the clover action - is constructed to have smaller discretization errors than the normal Wilson quark action. We test this in a quenched spectroscopy computation on 6 lattice ensembles with spacings from 0.15 to 0.43 fm. To ensure that the dominant scaling violations come from the fermions we use an $O(a^2)$ improved 6-link $SU(3)$ pure gauge action. We find evidence that fermionic scaling violations are consistent with $O(a^2)$ for clover fermions and $O(a)$...

Source: http://arxiv.org/abs/hep-lat/9611022v1

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Sep 21, 2013
09/13

by
P. H. Damgaard; U. M. Heller; R. Niclasen; K. Rummukainen

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Based on a large number of smearing steps, we classify SU(3) gauge field configurations in different topological sectors. For each sector we compare the exact analytical predictions for the microscopic Dirac operator spectrum of quenched staggered fermions. In all sectors we find perfect agreement with the predictions for the sector of topological charge zero, showing explicitly that the smallest Dirac operator eigenvalues of staggered fermions at presently realistic lattice couplings are...

Source: http://arxiv.org/abs/hep-lat/9907019v1

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Sep 22, 2013
09/13

by
G. Cella; U. M. Heller; V. K. Mitrjushkin; A. Vicere

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We study the heavy charge potential in the Coulomb phase of pure gauge compact U(1) theory on the lattice. We calculate the static potential $V_W(T,{\vec R})$ from Wilson loops on a $16^3 \times 32$ lattice and compare with the predictions of lattice perturbation theory. We investigate finite size effects and, in particular, the importance of non-Coulomb contributions to the potential. We also comment on the existence of a maximal coupling in the Coulomb phase of pure gauge U(1) theory.

Source: http://arxiv.org/abs/hep-lat/9704012v1

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Sep 17, 2013
09/13

by
P. H. Damgaard; U. M. Heller; R. Niclasen; K. Rummukainen

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We compute by Monte Carlo methods the individual distributions of the $k$th smallest Dirac operator eigenvalues in QCD, and compare them with recent analytical predictions. We do this for both massless and massive quarks in an SU(3) gauge theory with staggered fermions. Very precise agreement is found in all cases. As a simple by-product we also extract the microscopic spectral density of the Dirac operator in SU(3) gauge theory with dynamical massive fermions for $N_f=1$ and 2, and obtain...

Source: http://arxiv.org/abs/hep-lat/0007041v2

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Sep 18, 2013
09/13

by
P. H. Damgaard; U. M. Heller; A. Krasnitz; T. Madsen

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Three-dimensional lattice QCD is studied by Monte Carlo simulations within the quenched approximation. At zero temperature a quark-antiquark condensate is observed in the limit of vanishing quark masses. The condensate vanishes continuously at the finite-temperature deconfinement phase transition of the theory. A natural interpretation of this phenomenon in the full theory with dynamical quarks is in terms of the spontaneous flavor symmetry breaking $U(N_f) \to U(N_f/2)\times U(N_f/2)$. In...

Source: http://arxiv.org/abs/hep-lat/9803012v3

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Sep 23, 2013
09/13

by
P. H. Damgaard; U. M. Heller; R. Niclasen; K. Rummukainen

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We classify SU(3) gauge field configurations in different topological sectors by the smearing technique. In each sector we compute the distribution of low lying eigenvalues of the staggered Dirac operator. In all sectors we find perfect agreement with the predictions for the sector of topological charge zero. The smallest Dirac operator eigenvalues of staggered fermions at presently realistic lattice couplings are thus insensitive to gauge field topology. On the smeared configurations, $4\nu$...

Source: http://arxiv.org/abs/hep-lat/9909017v1

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Sep 18, 2013
09/13

by
P. H. Damgaard; U. M. Heller; R. Niclasen; B. Svetitsky

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It has been conjectured that spontaneous chiral symmetry breaking in strongly coupled vectorlike gauge theories falls into only three different classes, depending on the gauge group and the representations carried by the fermions. We test this proposal by studying SU(2), SU(3) and SU(4) lattice gauge theories with staggered fermions in different irreducible representations. Staggered fermions away from the continuum limit should, for all complex representations, still belong to the continuum...

Source: http://arxiv.org/abs/hep-lat/0110028v2

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Sep 22, 2013
09/13

by
P. H. Damgaard; U. M. Heller; R. Niclasen; K. Rummukainen

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We compute the low-lying spectrum of the staggered Dirac operator above and below the finite temperature phase transition in both quenched QCD and in dynamical four flavor QCD. In both cases we find, in the high temperature phase, a density with close to square root behavior, $\rho(\lambda) \sim (\lambda-\lambda_0)^{1/2}$. In the quenched simulations we find, in addition, a volume independent tail of small eigenvalues extending down to zero. In the dynamical simulations we also find a tail,...

Source: http://arxiv.org/abs/hep-lat/0003021v3

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Sep 18, 2013
09/13

by
LHP Collaboration; R. G. Edwards; U. M. Heller; D. G. Richards

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The calculation of the light-hadron spectrum in the quenched approximation to QCD using an anisotropic clover fermion action is presented. The tuning of the parameters of the action is discussed, using the pion and rho dispersion relation. The adoption of an anisotropic lattice provides clear advantages in the determination of the baryonic resonances, and in particular that of the so-called Roper resonance, the lightest radial excitation of the nucleon.

Source: http://arxiv.org/abs/hep-lat/0303004v1

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Sep 21, 2013
09/13

by
P. H. Damgaard; R. G. Edwards; U. M. Heller; R. Narayanan

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We confront exact analytical predictions for the finite-volume scaling of the chiral condensate with data from quenched lattice gauge theory simulations. Using staggered fermions in both the fundamental and adjoint representations, and gauge groups SU(2) and SU(3), we are able to test simultaneously all of the three chiral universality classes. With overlap fermions we also test the predictions for gauge field sectors of non-zero topological charge. Excellent agreement is found in most cases,...

Source: http://arxiv.org/abs/hep-lat/9907016v2

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Sep 18, 2013
09/13

by
Balasubramanian Krishnan; U. M. Heller; V. K. Mitrjushkin; M. Mueller-Preussker

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We investigate a model of a U(1)-Higgs theory on the lattice with compact gauge fields but completely suppressed (elementary) monopoles. We study the model at two values of the quartic Higgs self-coupling, a strong coupling, $\lambda = 3.0$, and a weak coupling, $\lambda=0.01$. We map out the phase diagrams and find that the monopole suppression eliminated the confined phase of the standard lattice model at strong gauge coupling. We perform a detailed analysis of the static potential and study...

Source: http://arxiv.org/abs/hep-lat/9605043v1

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Sep 23, 2013
09/13

by
P. H. Damgaard; R. G. Edwards; U. M. Heller; R. Narayanan

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In the large-volume limit $V\to\infty$ with $V < < 1/m_{\pi}^4$ the mass-dependent chiral condensate is predicted to satisfy exact finite-volume scaling laws that fall into three major universality classes. We test these analytical predictions with staggered fermions and overlap fermions in gauge field sectors of fixed topological charge $\nu$.

Source: http://arxiv.org/abs/hep-lat/9909009v1

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Sep 23, 2013
09/13

by
R. V. Gavai; U. M. Heller; F. Karsch; B. Plache; T. Neuhaus

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Results of investigations of the O(4) spin model at finite temperature using anisotropic lattices are presented. In both the large $N$ approximation and the numerical simulations using the Wolff cluster algorithm we find that the ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass $m_{\rm H}$ is independent of the anisotropy. We obtain a lower bound of $0.59 \pm 0.04$ for the ratio, $T_{\rm SR}/m_{\rm H}$, at $m_{\rm H}a \simeq 0.5$, which is lowered further by about...

Source: http://arxiv.org/abs/hep-lat/9201002v1

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Sep 20, 2013
09/13

by
G. S. Bali; J. Fingberg; U. M. Heller; F. Karsch; K. Schilling

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A detailed investigation of the temperature dependence of the spatial string tension $\sigma_s$ in $SU(2)$ gauge theory is presented. A sustained performance of 3~GFLOPS on a 64K Connection Machine CM-2 equivalent has been achieved. Scaling of $\sigma_s$ between $\beta=2.5115$ and $\beta=2.74$, on large lattices, is demonstrated. Below the critical temperature, $T_c$, $\sigma_s$ remains constant. For temperatures larger than $2T_c$ the temperature dependence can be parametrized by $\sigma_s(T)...

Source: http://arxiv.org/abs/hep-lat/9308003v2

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Sep 21, 2013
09/13

by
P. H. Damgaard; U. M. Heller; K. Splittorff; B. Svetitsky; D. Toublan

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We calculate the response of the microscopic Dirac spectrum to an imaginary isospin chemical potential for QCD with two dynamical flavors in the chiral limit. This extends our previous calculation from the quenched to the unquenched theory. The resulting spectral correlation function in the $\epsilon$-regime provides here, too, a new and efficient way to measure $F_\pi$ on the lattice. We test the method in a hybrid Monte Carlo simulation of the theory with two staggered quarks.

Source: http://arxiv.org/abs/hep-lat/0602030v1

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Sep 19, 2013
09/13

by
P. O. Bowman; U. M. Heller; D. B. Leinweber; A. G. Williams

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The Laplacian gauge is a nonperturbative gauge fixing that reduces to Landau gauge in the asymptotic limit. Like Landau gauge, it respects Lorentz invariance, but it is free of Gribov copies; the gauge fixing is unambiguous. In this paper we study the infrared behavior of the lattice gluon propagator in Laplacian gauge by using a variety of lattices with spacings from $a = 0.125$ to 0.35 fm, to explore finite volume and discretization effects. Three different implementations of the Laplacian...

Source: http://arxiv.org/abs/hep-lat/0206010v2

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Sep 19, 2013
09/13

by
P. O. Bowman; U. M. Heller; D. B. Leinweber; A. G. Williams

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The quark propagator is at the core of lattice hadron spectrum calculations as well as studies in other nonperturbative schemes. We investigate the quark propagator with an improved staggered action (Asqtad) and an improved gluon action, which provides good quality data down to small quark masses. This is used to construct ans\"{a}tze suitable for model hadron calculations as well as adding to our intuitive understanding of QCD.

Source: http://arxiv.org/abs/hep-lat/0209129v1

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Sep 22, 2013
09/13

by
K. M. Bitar; R. G. Edwards; U. M. Heller; A. D. Kennedy

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We test the asymptotic scaling behavior of state-of-the-art simulations of QCD with two flavors of light Wilson fermions. This is done by matching $\pi$ and $\rho$ masses on lattices of size $16^3\times32$ and $8^3\times16$. We find that at $\beta=6/g^2=5.3$ matching is not possible over a range extending down to $\beta=3.5$. The large lattice data at $\beta=5.5$ matches the small lattice values at $\beta=4.9(1)$ leading to a shift $\Delta\beta=0.6(1)$, considerably larger than the perturbative...

Source: http://arxiv.org/abs/hep-lat/9602010v2

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Sep 19, 2013
09/13

by
R. V. Gavai; U. M. Heller; F. Karsch; T. Neuhaus; B. Plache

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Results of an investigation of the $O(4)$ spin model at finite temperature using anisotropic lattices are presented. In both the large $N$ approximation and numerical simulations using the Wolff cluster algorithm we find that the ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass $m_{\rm H}$ is independent of the anisotropy $\xi$. From the numerical simulations we obtain a lower bound of $T_{\rm SR} / m_{\rm H} \simeq 0.58 \pm 0.02$ at a value for the Higgs mass...

Source: http://arxiv.org/abs/hep-lat/9207033v1

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Jul 19, 2013
07/13

by
U. M. Heller; Khalil M. Bitar; R. G. Edwards; A. D. Kennedy

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We compute the heavy quark potential on configurations generated by the HEMCGC collaboration with dynamical staggered fermions at $6/g^2 = 5.6$ and with dynamical Wilson fermions at $6/g^2 = 5.3$. The computations are done on $16^3 \times 32$ lattices, corresponding to physical sizes of about 1.6 and 2.3 fm, respectively. Up to the distances probed no sign of string breaking is detectable. We also compute the recently proposed scale $r_0$ defined by $r_0^2 F(r_0) = 1.65$.

Source: http://arxiv.org/abs/hep-lat/9401025v1

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Jul 20, 2013
07/13

by
P. H. Damgaard; U. M. Heller; K. Splittorff; B. Svetitsky; D. Toublan

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We consider the chiral limit of QCD subjected to an imaginary isospin chemical potential. In the epsilon-regime of the theory we can perform precise analytical calculations based on the zero-momentum Goldstone modes in the low-energy effective theory. We present results for the spectral correlation functions of the associated Dirac operators.

Source: http://arxiv.org/abs/hep-th/0604054v2

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Sep 23, 2013
09/13

by
K. M. Bitar; R. G. Edwards; U. M. Heller; A. D. Kennedy

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We study QCD with two flavors of dynamical Wilson fermions at $\beta = 5.5$ and three values of $\kappa$. The corresponding pion masses are 0.375, 0.324 and 0.262 in lattice units, with pion to rho mass ratios of 0.76, 0.71 and 0.62, respectively. We use the configurations to compute the heavy quark potential, leading to lattice spacings of 0.110, 0.105 and 0.099 fm, and to compute spectroscopy for several different valence quark $\kappa$'s.

Source: http://arxiv.org/abs/hep-lat/9607043v1

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Sep 22, 2013
09/13

by
G. S. Bali; J. Fingberg; U. M. Heller; F. Karsch; K. Schilling

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We present results of a detailed investigation of the temperature dependence of the spatial string tension in SU(2) gauge theory. We show, for the first time, that the spatial string tension is scaling on the lattice and thus is non-vanishing in the continuum limit. It is temperature independent below Tc and rises rapidly above. For temperatures larger than 2Tc we find a scaling behaviour consistent with sigma_s(T) = 0.136(11) g^4(T) T^2, where g(T) is the 2-loop running coupling constant with...

Source: http://arxiv.org/abs/hep-lat/9306024v1

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Sep 22, 2013
09/13

by
S. Collins; U. M. Heller; J. Sloan; J. Shigemitsu; A. Ali Khan; C. Davies

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We present a lattice investigation, partially including the effects of dynamical quarks, of the heavy-light mesons using NRQCD for the heavy quark and the Wilson action for the light quark. We performed an extensive calculation of the spectrum employing a multi-state, multi-exponential fitting analysis which enabled us to extract the $2S{-}1S$ splitting as well as the $^1P_1{-}\bar{S}$ and hyperfine splittings. The Wilson action introduces a large systematic error into the calculation, and...

Source: http://arxiv.org/abs/hep-lat/9602028v1

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Sep 18, 2013
09/13

by
S. Collins; U. M. Heller; J. Sloan; J. Shigemitsu; A. Ali-Khan; C. Davies

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We present {\it preliminary} results for the decay constants of heavy-light mesons using NRQCD heavy and tadpole improved Clover light quarks. A comparison is made with data obtained using Wilson light quarks. We present an analysis of the 1/M corrections to the decay constants in the static limit and compare with the predictions of HQET.

Source: http://arxiv.org/abs/hep-lat/9509065v1

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Jul 20, 2013
07/13

by
K. M. Bitar; R. G. Edwards; U. M. Heller; A. D. Kennedy; P. Vranas

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We present data for the scaling behavior of lattice QCD with two flavors of light Wilson fermions. This is done by matching $\pi$ n and $\rho$ masses at the two lattice sizes of $16^3\times32 $ and $8^3\times16$. We find that at $\beta=6/g^2\equiv5.3$ the matching does not occur over a range extending down to $\beta=3.5$. For $\beta=5.5$ matching may be achieved at $\beta=4.8-4.9$, leading to a $\Delta \beta =0.6-0.7$ which is higher than the perturbative 2-loop value of 0.45. In both cases we...

Source: http://arxiv.org/abs/hep-lat/9411057v1