Braaten-Pisarski Action, Disoriented Chiral Condensate, and Chiral Symmetry Non-Restoration

Abstract

The QCD effective action at high T shows a manifest global chiral symmetry. And calculations show that the order parameter \psibarpsi vanishes above T_c. It has been popular to refer to this T_c as chiral symmetry restoration temperature because it fits into our prejudice that chiral symmetry is like an `ordered' state, and at high T it must become disordered. In fact, NJL ground state is not an ordered spin state. The recent scenario of a generic class of disoriented chiral condensate offers an example where \psibarpsi in each little domain is nonzero, but the average over all space of \psibarpsi vanishes. Such a dcc ground state continues to break chiral invariance. But how do you reconcile this with the apparent chiral symmetry at high T? The Braaten-Pisarski action is a good laboratory to investigate the subtleties of high temperature chiral symmetry. By carrying out a canonical quantization of this highly nonlocal action, I demonstrate how the thermal vacuum at high T conserves the new β-chirality but breaks the old T=0 chirality. Lattice calculations show that the pion develops a screening mass at high T. Our continuum field theory calculations show that the QCD pion remains massless for all T. I conclude the talk by showing how the hot pion manages to accomodate the two results by propagating in the early universe with a halo.