Hawking Radiation, Covariant Boundary Conditions and Vacuum States

The basic characteristics of the covariant chiral current $<J_{mu}>$ and the covariant chiral energy-momentum tensor $<T_{mu u}>$ are obtained from a chiral effective action. These results are used to justify the covariant boundary condition used in recent approaches cite{Isowilczek,Isoumtwilczek,shailesh,shailesh2,Banerjee} of computing the Hawking flux from chiral gauge and gravitational anomalies. We also discuss a connection of our results with the conventional calculation of nonchiral currents and stress tensors in different (Unruh, Hartle-Hawking and Boulware) states.