Thermodynamics with Improved Staggered Quarks

	Figure 3   The energy density (top) and pressure (bottom) of free massless fermions as function of temporal lattice size Nt. For free fermions the “Asqtad” action reduces to the Naik action.

With the Relativistic Heavy Ion Collider now producing data, it has become even more important to understand the phase diagram of QCD at finite temperature, and to determine properties of the high temperature quark-gluon plasma phase with confidence, i.e., with controlled lattice spacing errors.

The MILC Collaboration has published preliminary results from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. The simulations used an improved staggered fermion action, the “Asqtad” action, which reduces flavor symmetry breaking so that all pions are lighter than the kaon already at larger lattice spacing. This action also improves rotational symmetry and the dispersion relation, leading to diminished lattice artifacts in energy density and pressure (Figure 3).

INVESTIGATORS
D. Toussaint and T. Burch, University of Arizona; C. Bernard, Washington University; S. Datta and S. Gottlieb, Indiana University; T. A. DeGrand, University of Colorado; C. E. DeTar, University of Utah; U. M. Heller, Florida State University; K. Orginos, Brookhaven National Laboratory; R. L. Sugar, University of California, Santa Barbara.

PUBLICATION
C. Bernard, T. Burch, S. Datta, T. A. DeGrand, C. E. DeTar, S. Gottlieb, U. M. Heller, K. Orginos, R. L. Sugar, and D. Toussaint, “Thermodynamics with 2+1 and 3 flavors of improved staggered quarks,” Nucl. Phys. A 702, 140 (2002).

URL
http://www.physics.ucsb.edu/~sugar/poster.ps