The chiral transition of N_f=2 QCD with fundamental and adjoint fermions

Abstract

We study QCD with two staggered Dirac fermions both in the fundamental (QCD) and the adjoint representation (aQCD) near the chiral transition. The aim is to find the universality class of the chiral transition and to verify Goldstone effects below the transition. We investigate aQCD, because in that theory the deconfinement and the chiral transitions occur at different temperatures T_d<T_c. Here, we show that the scaling behaviour of the chiral condensate in the vicinity of β_c is in full agreeement with that of the 3d O(2) universality class. In the region T_d<T<T_c we 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. For fundamental QCD we use the p4-action. Here, we find Goldstone effects below T_c like in aQCD and the 3d O(N) spin models, however no O(2)/O(4) scaling near the chiral transition point. The result for QCD may be a consequence of the coincidence of the deconfinement transition with the chiral transition.