出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We study the nature of the finite-temperature chiral transition in QCD with Nf light quarks in
the fundamental and adjoint representation. Universality and renormalization-group (RG) arguments
show that the possibility of having a continuous transition is related to the existence of a
stable fixed point (FP) in the RG flow of a 3D Landau-Ginzburg-WilsonF4 theory with the same
chiral symmetry-breaking pattern. The RG flow of these theories is studied by field-theoretical
approaches, computing and analyzing high-order perturbative series, up to six loops. According
to this RG analysis, the transition in QCD can be continuous only for Nf 2. In this case it
belongs to the 3D O(4) universality class. We also find a stable FP corresponding to a 3D universality
class with symmetry breaking U(2)L U(2)R
U(2)V , which implies that the transition can
be continuous also if the axial-anomaly effects are suppressed at Tc. In the case of quarks in the
adjoint representation, we can have a continuous transition for Nf 1
2. For Nf 1 it belongs
to the O(3) universality class. For Nf 2 it belongs to a new 3D universality class characterized
by the symmetry breaking SU(4)
SO(4).
