Extremal Limits of Rotating Black Holes

TL;DR

This paper develops an algebraic method to connect non-extremal rotating black holes with extremal solutions in supergravity, revealing a continuous interpolation and generalizing previous limits, with detailed examples in specific models.

Contribution

It introduces a general algebraic procedure for deriving extremal limits of rotating black holes from non-extremal solutions in supergravity models, extending known methods.

Findings

The algebraic procedure generalizes the Rasheed-Larsen limit.

Non-extremal solutions can be viewed as interpolating among extremal limits.

Explicit example provided in the T^3-model with detailed solution analysis.

Abstract

We consider non-extremal, stationary, axion-dilaton solutions to ungauged symmetric supergravity models, obtained by Harrison transformations of the non-extremal Kerr solution. We define a general algebraic procedure, which can be viewed as an Inonu-Wigner contraction of the Noether charge matrix associated with the effective D=3 sigma-model description of the solution, yielding, through different singular limits, the known BPS and non-BPS extremal black holes (which include the under-rotating non-BPS one). The non-extremal black hole can thus be thought of as "interpolating" among these limit-solutions. The algebraic procedure that we define generalizes the known Rasheed-Larsen limit which yielded, in the Kaluza-Klein theory, the first instance of under-rotating extremal solution. As an example of our general result, we discuss in detail the non-extremal solution in the T^3-model, with either (q_0, p^1) or (p^0, q_1) charges switched on, and its singular limits. Such solutions, computed in D=3 through the solution-generating technique, is completely described in terms of D=4 fields, which include the fully integrated vector fields.