We investigate chiral-restoration patterns of QCD for N_{ c}=3 and N_{ f}=2 at finite temperature (T) and zero quark-chemical potential beyond the chiral limit, indicating the explicit chiral-symmetry breaking. To this end, we employ the instanton-vacuum configuration for the flavor SU(2) sector and the Harrington-Shepard caloron for modifying relevant instanton parameters as functions of T. The meson-loop corrections (MLC), which correspond to 1/N_{ c} corrections, are also taken into account to reproduce appropriate m_{ q} dependences of chiral order parameters. We compute chiral condensate as a function of T and/or m_{ q}. From the numerical calculations, we observe that MLC play an important role to have a correct universality-class behavior of chiral-restoration patterns in this framework, depending on m_{ q}: Second-order phase transition in the chiral limit, m_{ q}=0 and crossover for m_{ q}>0. Without MLC, all the restoration patterns are crossover, due to simple saddle-point approximations. It turns out that T^{ \chi}_{ c}=159 MeV in the chiral limit and T^{ \chi}_{ c}=(177,186,196) MeV for m_{ q}=(5,10,15) MeV, using the phenomenological choices for the instanton parameters at T=0.
Categories: hep-ph nucl-th