Black Holes with Primary Hair in gauged N=8 Supergravity

TL;DR

This paper presents the first exact example of a black hole with primary scalar hair in gauged N=8 supergravity, analyzing static solutions and their thermodynamic phase structure, including symmetry breaking and phase transitions.

Contribution

It introduces a new parametrization revealing three black hole configurations, notably the first exact primary hair solution with regular scalar fields outside the horizon.

Findings

Existence of three black hole solutions with different scalar hair patterns.

Identification of a triple point where all three solutions coexist.

Explicit thermodynamic free energies for uncharged and charged cases.

Abstract

In this paper, we analyze the static solutions for the $U(1)^{4}$ consistent truncation of the maximally supersymmetric gauged supergravity in four dimensions. Using a new parametrization of the known solutions it is shown that for fixed charges there exist three possible black hole configurations according to the pattern of symmetry breaking of the (scalars sector of the) Lagrangian. Namely a black hole without scalar fields, a black hole with a primary hair and a black hole with a secondary hair respectively. This is the first, exact, example of a black hole with a primary scalar hair, where both the black hole and the scalar fields are regular on and outside the horizon. The configurations with secondary and primary hair can be interpreted as a spontaneous symmetry breaking of discrete permutation and reflection symmetries of the action. It is shown that there exist a triple point in the thermodynamic phase space where the three solution coexist. The corresponding phase transitions are discussed and the free energies are written explicitly as function of the thermodynamic coordinates in the uncharged case. In the charged case the free energies of the primary hair and the hairless black hole are also given as functions of the thermodynamic coordinates.