General Kerr-NUT-AdS Metrics in All Dimensions

TL;DR

This paper derives the most general Kerr-NUT-AdS metrics in all dimensions, introduces a new coordinate system simplifying the metric, and explores symmetries and special limits leading to Einstein-Sasaki spaces.

Contribution

It provides a unified, diagonal form of Kerr-NUT-AdS metrics in all dimensions and introduces new NUT parameters, revealing symmetries and special geometric limits.

Findings

Derived the most general Kerr-NUT-AdS metrics in all dimensions.

Introduced a coordinate reparameterisation making the metric diagonal.

Discovered discrete symmetries relating over-rotating and under-rotating metrics.

Abstract

The Kerr-AdS metric in dimension D has cohomogeneity [D/2]; the metric components depend on the radial coordinate r and [D/2] latitude variables \mu_i that are subject to the constraint \sum_i \mu_i^2=1. We find a coordinate reparameterisation in which the \mu_i variables are replaced by [D/2]-1 unconstrained coordinates y_\alpha, and having the remarkable property that the Kerr-AdS metric becomes diagonal in the coordinate differentials dy_\alpha. The coordinates r and y_\alpha now appear in a very symmetrical way in the metric, leading to an immediate generalisation in which we can introduce [D/2]-1 NUT parameters. We find that (D-5)/2 are non-trivial in odd dimensions, whilst (D-2)/2 are non-trivial in even dimensions. This gives the most general Kerr-NUT-AdS metric in $D$ dimensions. We find that in all dimensions D\ge4 there exist discrete symmetries that involve inverting a rotation parameter through the AdS radius. These symmetries imply that Kerr-NUT-AdS metrics with over-rotating parameters are equivalent to under-rotating metrics. We also consider the BPS limit of the Kerr-NUT-AdS metrics, and thereby obtain, in odd dimensions and after Euclideanisation, new families of Einstein-Sasaki metrics.