Phases of planar AdS black holes with axionic charge

TL;DR

This paper introduces a new family of exact asymptotically AdS4 black branes with scalar hair, magnetic and axion charges, analyzing their thermodynamics, stability, and holographic properties, with implications for momentum relaxation and conductivity.

Contribution

It presents novel exact solutions of AdS black branes with scalar hair and axionic charge, and explores their thermodynamics and stability under mixed boundary conditions.

Findings

New exact asymptotically AdS4 black brane solutions with scalar hair.

Proper scalar boundary conditions ensure well-defined thermodynamics.

Dynamical stability linked to positivity of energy density.

Abstract

Planar AdS black holes with axionic charge have finite DC conductivity due to momentum relaxation. We obtain a new family of exact asymptotically AdS$_4$ black branes with scalar hair, carrying magnetic and axion charge, and we study the thermodynamics and dynamic stability of these, as well as of a number of previously known electric and dyonic solutions with axion charge and scalar hair. The scalar hair for all solutions satisfy mixed boundary conditions, which lead to modified holographic Ward identities, conserved charges and free energy, relative to those following from the more standard Dirichlet boundary conditions. We show that properly accounting for the scalar boundary conditions leads to well defined first law and other thermodynamic relations. Finally, we compute the holographic quantum effective potential for the dual scalar operator and show that dynamical stability of the hairy black branes is equivalent to positivity of the energy density.