Dissipative field theory with the Caldeira-Leggett method and its application to disoriented chiral condensation

The effective field theory including the dissipative effect is developed based on the Caldeira-Leggett theory at the classical level. After the integration of the small field fluctuations considered as the field radiation, the integrodifferential field equation is given and shown to include dissipative effects. In that derivation, special care should be taken for the boundary condition of the integration. Application to the linear σ model is given, and the decay process of the chiral condensate is calculated with it, both analytically in the linear approximation and numerically. With these results, we discuss the stability of chiral condensates within the quenched approximation.