Kodama-like Vector Fields in Axisymmetric Spacetimes

Abstract

We extend the concept of the Kodama symmetry, a quasi-local time translation symmetry for dynamical spherically symmetric spacetimes, to a specific class of dynamical axisymmetric spacetimes, namely the families of Kerr-Vaidya and Kerr-Vaidya-de Sitter spacetimes. We study some geometrical properties of the asymptotically flat Kerr-Vaidya metric, such as the Brown-York mass and the Einstein tensor. Furthermore, we propose a generalization of the Kerr-Vaidya metric to an asymptotic de Sitter background. We show that for these classes of dynamical axisymmetric black hole spacetimes, there exists a timelike vector field that exhibits similar properties to the Kodama vector field in spherical symmetry. This includes the construction of a covariantly conserved current and a corresponding locally conserved charge, which in the Kerr-Vaidya case converges to the Brown-York mass in the asymptotically flat region.