CHIRAL-SYMMETRY RESTORATION AND PARITY MIXING

We derive the expressions of the (isovector) vector and axial current from a chiral Lagrangian restricted to nucleons and pions. We show tha t in the heat bath certain terms call induce a mixing of the axial cur rent into the vector one and vice versa. We generalize this concept to the case of a dense baryonic medium. We study the subsequent modifica tions of the axial nucleonic coupling constant and the pion decay one. They arise from a two pion exchange current of a new type. We discuss the link to the condensate evolution. The quenching of the axial coup ling constant helps explaining the observed one of the Gamow-Teller su m rule.