Scaling study of the two-flavor chiral phase transition with the Kogut-Susskind quark action in lattice QCD

We report on a study of the two-flavor finite-temperature chiral phase transition employing the Kogut-Susskind quark action and the plaquette gluon action in lattice QCD for a lattice with N-t=4 temporal size. Hybrid R simulations of 10(4) trajectories are made at quark masses of m(q) = 0.075,0.0375,0.02,0.01 in lattice units for the spatial sizes 8(3), 12(3), and 16(3). The spatial size dependence of various susceptibilities confirm the previous conclusion of the absence of a phase transition down to m(q)=0.02. At m(q)=0.01 an increase of susceptibilities is observed up to the largest volume 16(3) explored in the present work. We argue, however, that this increase is likely to be due to an artifact of too small a lattice size and it cannot be taken to be the evidence for a first-order transition. Analysis of critical exponents estimated from the quark mass dependence of susceptibilities shows that they satisfy hyperscaling consistent with a second-order transition located at m(q)=0. The exponents obtained from larger lattice, however, deviate significantly from both those of O(2), which is the exact symmetry group of the Kogut-Susskind action at finite lattice spacing, and those of O(4) expected from an effective sigma model analysis in the continuum limit. [S0556-2821(98)04107-1].