Scaling and Goldstone effects in a QCD with two flavours of adjoint quarks

Abstract

We study QCD with two Dirac fermions in the adjoint representation at finite temperature by Monte Carlo simulations.In such a theory the deconfinement and chiral phase transitions occur at different temperatures. We locate the second order chiral transition point at beta_c=5.624(2) and show that the scaling behaviour of the chiral condensate in the vicinity of beta_c is in full agreeement with that of the 3d O(2) universality class, and to a smaller extent comparable to the 3d O(6) class. From the previously determined first order deconfinement transition point beta_d=5.236(3) and the two-loop beta function we find the ratio T_c/T_d = 7.8(2). In the region between the two phase transitions we explicitly confirm the quark mass dependence of the chiral condensate which is expected due to the existence of Goldstone modes like in 3d O(N) spin models. At the deconfinement transition the condensate shows a gap, and below beta_d, it is nearly mass-independent for fixed beta.