AdS$_3$ black holes with primary Proca hair from a regularized Gauss-Bonnet coupling
Gokhan Alkac, Murat Mesta, Gonul Unal
TL;DR
This work introduces a consistent three-dimensional Einstein-Gauss-Bonnet framework within the generalized Proca class by regularizing the Gauss-Bonnet term through Weyl geometry. It derives an asymptotically $AdS_3$ black-hole solution with primary Proca hair, and analyzes how adding a scalar-tensor Gauss-Bonnet term and electric charge modifies the geometry, including regular and stealth BTZ branches. The key contributions are the explicit 3d vector-tensor Lagrangian with a closed-form reduced action, the Noether-charge–driven solution for a hair-bearing black hole, and the exploration of charged and nontrivially coupled generalizations. The findings provide a testbed for AdS$_3$/CFT$_2$ holography with hair, and they suggest directions for thermodynamics, rotations, and holographic entropy in these lower-dimensional higher-curvature theories.
Abstract
We construct a consistent three-dimensional Einstein-Gauss-Bonnet theory as a vector-tensor theory within the generalized Proca class by employing a regularization procedure based on the Weyl geometry, which was introduced recently in \link{2504.13084}. We then obtain an asymptotically AdS$_3$, static, and circularly symmetric black hole solution with primary Proca hair. Afterward, we investigate the effect of the scalar-tensor Gauss-Bonnet coupling constructed previously by different regularization schemes. We further generalize these solutions by incorporating an electric charge. As special cases, we find a regular black hole solution in addition to charged and uncharged stealth BTZ black hole solutions.
