The cosmological constant as a thermodynamic black hole parameter

One may consider the cosmological constant Λ as a dynamical variable in general relativity. The simplest way of doing this is to couple the gravitational field to a three-index tensor. In a black hole solution Λ appears then as an integration constant (''hair'') in a similar footing with the total mass and charges of the hole. There is a quantum process of radiation of bubbles, analogous to particle emission, which spontaneously reduces Λ. The general laws of black hole thermodynamics still appear to hold. (orig.)