Effective action and thermodynamics of radiating shells in general relativity

An effective action is obtained for the area and mass aspect of a thin shell of radiating self-gravitating matter. On following a mini-superspace approach, the geometry of the embedding space-time is not dynamical but fixed to be either Minkowski or Schwarzschild inside the shell and Vaidya in the external space filled with radiation. The Euler-Lagrange equations of motion are discussed and shown to entail the expected invariance of the effective Lagrangian under time reparametrization. They are equivalent to the usual junction equations and suggest a macroscopic quasi-static thermodynamic description. [S0556-2821(99)00324-0].