arXiv subjects

R. L. Sugar

Publications and source records attributed to R. L. Sugar.

64 records · Page 4Linked to original sources

arXiv1994

Competition Between Antiferromagnetic Order and Spin-Liquid Behavior in the Two-Dimensional Periodic Anderson Model at Half-Filling

We study the two-dimensional periodic Anderson model at half-filling using quantum Monte Carlo (QMC) techniques. The ground state undergoes a magnetic order-disorder transition as a function of the effective exchange coupling between the conduction and localized bands. Low-lying spin and charge excitations are determined using the maximum entropy method to analytically continue the QMC data. At finite temperature we find a competition between the Kondo effect and antiferromagnetic order which develops in the localized band through Ruderman-Kittel-Kasuya-Yosida interactions.

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

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

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↗