Collision of light-like shells and mass inflation in rotating black holes

The authors extend to the case where no symmetries are present the Dray-'t Hooft-Redmount relation, expressing conservation of energy in the collision of two light-like thin shells. This relation is applied to a schematic model for the internal physics of a rotating black hole. They show that Hawking's quasi-local mass increases without limit near the Cauchy horizon. Previous arguments for mass inflation in spherical black holes are thus extended to the generic case.