arXiv subjects

D. Toussaint

Publications and source records attributed to D. Toussaint.

178 records · Page 10Linked to original sources

arXiv1994

Thermal Phase Transition in Mixed Action SU(3) Lattice Gauge Theory and Wilson Fermion Thermodynamics

We study the thermal phase diagram of pure SU(3) lattice gauge theory with fundamental and adjoint couplings. We improve previous estimates of the position of the bulk transition line and determine the thermal deconfinement transition lines for $N_t=2,4,6,$ and 8. The endpoint of the bulk transition line $(β_f, β_a)=(4.00(7), 2.06(8))$ improves upon earlier estimates obtained using smaller lattice sizes. For $N_t > 4$ the deconfinement transition line splits cleanly away from the bulk transition line. With increasing $N_t$ the thermal deconfinement transition lines shift to increasingly weaker coupling, joining onto the bulk transition line at increasingly larger $β_a$ in a pattern consistent with the usual universality picture of lattice gauge theories. We also discuss the possible consequences of an induced adjoint term from the fermionic determinant and determine this induced term numerically with a microcanonical demon method for two flavors of dynamical Wilson fermions.

hep-lat↗

arXiv1994

Preliminary heavy-light decay constants from the MILC collaboration

Preliminary results from the MILC collaboration for $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios are presented. We compute in the quenched approximation at $β=6.3$, 6.0 and 5.7 with Wilson light quarks and static and Wilson heavy quarks. We attempt to quantify systematic errors due to finite volume, finite lattice spacing, large $am$, and fitting and extrapolation uncertainties. The hopping parameter approach of Henty and Kenway is used to treat the heavy quarks; the sources are Coulomb gauge gaussians.

hep-lat↗

arXiv1994

SU(3) Lattice Gauge Theory With Adjoint Action At Nonzero Temperature

We study the thermal phase diagram of pure SU(3) gauge theory with fundamental and adjoint couplings. We improve previous estimates of the position of the bulk transition line and determine the thermal deconfinement transition lines for $N_t=2,4,6,$ and 8. For $N_t > 4$ the deconfinement transition line splits cleanly away from the bulk transition line. With increasing $N_t$ the thermal deconfinement transition lines shift to increasingly weaker coupling, joining onto the bulk transition line at increasingly larger $β_a$ in a pattern consistent with the usual universality picture of lattice gauge theories.

hep-lat↗

arXiv1994

The beta function and equation of state for QCD with two flavors of quarks

We measure the pressure and energy density of two flavor QCD in a wide range of quark masses and temperatures. The pressure is obtained from an integral over the average plaquette or psi-bar-psi. We measure the QCD beta function, including the anomalous dimension of the quark mass, in new Monte Carlo simulations and from results in the literature. We use it to find the interaction measure, E-3p, yielding non-perturbative values for both the energy density E and the pressure p. uuencoded compressed PostScript file Revised version should work on more PostScript printers.

hep-lat↗

arXiv1994

Metal-insulator and insulator-insulator transitions in the quarter-filled band organic conductors

The theory of the 2k_F and 4k_F instabilities in quarter-filled band organic conductors is revisited. The phase angles of the 2k_F bond and charge density waves are shown to change as electron correlation is turned on, and this switching of the phase angle is critical for understanding the bond distortion patterns in the real materials. Intersite Coulomb interactions in the real materials must be nonzero but less than a critical value. Both intersite and intrasite charge density waves are destabilized in the quasi-two-dimensional regime for realistic parameters, thus explaining the weakening of these phases in the superconducting materials.

cond-mat↗

arXiv1994

QCD thermodynamics with Wilson quarks at large kappa

We have extended our study of the high temperature transition with two flavors of Wilson quarks on 12^3 x 6 lattices to kappa=0.19. We have also performed spectrum calculations on 12^3 x 24 lattices at kappa=0.19 to find the physical lattice spacing and quark mass. At this value of kappa the transition is remarkable in that the plaquette and psi-bar-psi show a large discontinuity while the Polyakov loop changes very little. This and several other features of the transition are more suggestive of a bulk transition than a transition to a quark-gluon plasma. However, if the temperature is estimated using the rho mass as a standard, the result is about 150 MeV, in agreement with the value found for the thermal transition with Kogut-Susskind quarks. uuencoded compressed Postscript file

hep-lat↗

arXiv1993

Effects of spatial size, lattice doubling and source operator on the hadron spectrum with dynamical staggered quarks

We have extended our previous study of the lattice QCD spectrum with 2 flavors of staggered dynamical quarks at $6/g^2=5.6$ and $am_q=0.025$ and 0.01 to larger lattices, with better statistics and with additional sources for the propagators. The additional sources allowed us to estimate the $Δ$ mass and to measure the masses of all mesons whose operators are local in time. These mesons show good evidence for flavor symmetry restoration, except for the masses of the Goldstone and non-Goldstone pions. PCAC is observed in that $m_π^2 \propto m_q$, and $f_π$ is estimated. Use of undoubled lattices removes problems with the pion propagator found in our earlier work. Previously we found a large change in the nucleon mass at a quark mass of $am_q=0.01$ when we increased the spatial size from 12 to 16. No such effect is observed at the larger quark mass, $am_q=0.025$. Two kinds of wall source were used, and we have found difficulties in getting consistent results for the nucleon mass between the two sources.

hep-lat↗

arXiv1993

The nature of the thermal phase transition with Wilson quarks

We describe a series of simulations of high temperature QCD with two flavors of Wilson quarks aimed at clarifying the nature of the high temperature phase found in current simulations. Most of our work is with four time slices, although we include some runs with six and eight time slices for comparison. In addition to the usual thermodynamic observables we study the quark mass defined by the divergence of the axial current and the quark propagator in the Landau gauge. We find that the sharpness of the $N_t=4$ thermal transition has a maximum around $κ=0.19$ and $6/g^2=4.8$.

hep-lat↗

arXiv1993

Finite-size and quark mass effects on the QCD spectrum with two flavors

We have carried out spectrum calculations with two flavors of dynamical Kogut-Susskind quarks on four lattice sizes from $8^3\times 24$ to $16^3\times24$ at couplings that correspond to chiral symmetry restoration for a lattice with 6 time slices. We estimate that the linear spatial sizes of the lattices range from 1.8 to 3.6 fm. We find significant finite size effects for all particles between the smallest and largest volume with the larger quark mass that we study, $am_q=0.025$, where $a$ is the lattice spacing. The nucleon experiences the largest effect of about 6 percent. We also study a lighter quark mass, $am_q=0.0125$, on the two largest lattices. Effects of the dynamical and valence quark masses on the hadron spectrum are studied both directly, by comparing the two simulations, and by extracting mass derivatives from the correlation functions. We do not find much improvement in the nucleon to rho mass ratio as we decrease the quark mass at this lattice spacing. Finally, we report on an unsuccessful attempt to see effects of the $ρ\rightarrow 2π$ decay on the $ρ$ mass, and on studies of Wilson and Kogut-Susskind hadron masses with large valence quark masses. (The paper is also available via anonymous ftp in a compressed PostScript file: fuji.physics.indiana.edu:/pub/milc/paper.ps.Z .)

hep-lat↗

arXiv1993

Simple Hadronic Matrix Elements with Wilson Valence Quarks and Dynamical Staggered Fermions at ${\bf 6/g^2=5.6}$

We have measured some simple matrix elements for pseudoscalar and vector mesons made of Wilson valence quarks and staggered sea quarks at $β=5.6$ at sea quark masses $am_q=0.01$ and 0.025. Our measurements include the decay constants of pseudoscalars (including $f_D$), the wave function at the origin (or decay constant) of vector mesons, and the calculation of quark masses from current algebra. The effects of sea quarks on the simulations are small. We make comparisons to quenched simulations at similar values of the lattice spacing ($1/a \simeq 2$ GeV).

hep-lat↗

arXiv1992

Baryon Density Correlations in the Quark Plasma, MIMD Lattice Calculation

As part of an ongoing effort to characterize the high temperature phase of QCD, we measure the quark baryon density in the vicinity of a fixed test quark and compare it with similar measurements at low temperature and at the crossover temperature. Such an observable has also been studied by the Vienna group. We find an extremely weak correlation at high temperature, suggesting that small color singlet clusters are unimportant in the thermal ensemble. We also find that at T = 0.75 T_c the induced quark number shows a surprisingly large component attributable to baryonic screening. A simulation of a simple flux tube model produces results that suggest a plausible scenario: As the crossover temperature is approached from below, baryonic states proliferate. Above the crossover temperature the mean size of color singlet clusters grows explosively, resulting in an effective electrostatic deconfinement.

hep-lat↗

arXiv1992

Finite Size Effects on the QCD Spectrum Revisited

We have continued our study of finite size effects in the QCD spectrum on lattices ranging in size from $8^3\times 24$ to $16^3\times24$. We have increased our statistics for quark mass $am_q=0.025$ for the smallest lattice size. In addition, we have studied quark mass 0.0125 for lattice sizes $12^3\times24$ and $16^3\times24$. These lattice sizes correspond to a box 1.8--3.6 fm on a side when the rho mass at zero quark mass is used to set the scale. We discuss the nucleon to rho mass ratio at a smaller value of $m_π/m_ρ$ than previously studied with two dynamical flavors.

hep-lat↗

arXiv1992

QCD thermodynamics with two flavors of Wilson quarks at N_t=6

We report on a study of hadron thermodynamics with two flavors of Wilson quarks on 12^3x6 lattices. We have studied the crossover between the high and low temperature regimes for three values of the hopping parameter, kappa=0.16, 0.17, and 0.18. At each of these values of kappa we have carried out spectrum calculations on 12^3x24 lattices for two values of the gauge coupling in the vicinity of the crossover in order to set an energy scale for our thermodynamics calculations and to determine the critical value of the gauge coupling for which the pion and quark masses vanish. For kappa=0.17 and 0.18 we find coexistence between the high and low temperature regimes over 1,000 simulation time units indicating either that the equilibration time is extremely long or that there is a possibility of a first order phase transition. The pion mass is large at the crossover values of the gauge coupling, but the crossover curve has moved closer to the critical curve along which the pion and quark masses vanish, than it was on lattices with four time slices. In addition, values of the dimensionless quantity T_c/m_rho are in closer agreement with those for staggered quarks than was the case at N_t=4. (A POSTSCRIPT VERSION OF THIS PAPER IS AVAILABLE BY ANONYMOUS FTP FROM sarek.physics.ucsb.edu (128.111.8.250) IN THE FILE pub/wilson_thermo.ps)

hep-lat↗

arXiv1992

Hadron Spectrum in QCD with Valence Wilson Fermions and Dynamical Staggered Fermions at $6/g^2=5.6

We present an analysis of hadronic spectroscopy for Wilson valence quarks with dynamical staggered fermions at lattice coupling $6/g^2 = β=5.6$ at sea quark mass $am_q=0.01$ and 0.025, and of Wilson valence quarks in quenched approximation at $β=5.85$ and 5.95, both on $16^3 \times 32$ lattices. We make comparisons with our previous results with dynamical staggered fermions at the same parameter values but on $16^4$ lattices doubled in the temporal direction.

hep-lat↗

arXiv1992

QCD Hadron Spectroscopy with Staggered Dynamical Quarks at $β= 5.6$

We present preliminary results from the 1991 HEMCGC simulations with staggered dynamical fermions on a $16^3 \times 32$ lattice at $β= 5.6$ with sea quark masses $am_q = 0.025$ and 0.01. The spectroscopy was done both for staggered valence quarks with mass equal to the sea quark masses and for Wilson valence quarks at six different values for $κ$, 0.1320, 0.1410, 0.1525, 0.1565, 0.1585, and 0.1600. In addition to the measurements performed in our earlier work, we also measured the $Δ$ and other `extended' hadrons for staggered valence quarks and pseudo-scalar decay constants and vector meson matrix elements, the wave function at the origin, for Wilson valence quarks.

hep-lat↗

arXiv1992

Thermodynamics of Lattice QCD with 2 Light Dynamical (Staggered) Quark Flavours on a $16^3\times 8$ Lattice

Lattice QCD with 2 light staggered quark flavours is being simulated on a $16^3\times8$ lattice to study the transition from hadronic matter to a quark gluon plasma. We have completed runs at $m_q=0.0125$ and are extending this to $m_q=0.00625$. We also examine the addition of a non-dynamical "strange" quark. Thermodynamic order parameters are being measured across the transition and further into the plasma phase, as are various screening lengths. No evidence for a first order transition is seen, and we estimate the transition temperature to be $TY_c=143(7) MeV$.

hep-lat↗