When AdS$_3$ Grows Hair: Boson Stars, Black Holes, and Double-Trace Deformations

Fuente: arXiv
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Auteurs principaux: Dias, Oscar J. C., Gil, David Sola, Santos, Jorge E.
Format: Preprint
Publié: 2026
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author Dias, Oscar J. C.
Gil, David Sola
Santos, Jorge E.
author_facet Dias, Oscar J. C.
Gil, David Sola
Santos, Jorge E.
contents We analyse three-dimensional Einstein gravity coupled to a massive complex scalar field with double-trace boundary conditions. Using high-precision spectral methods, we construct regular AdS$_3$ boson stars together with axisymmetric and non-axisymmetric hairy black holes. For each azimuthal number $m$, the hairy black holes bifurcate from the BTZ family at the corresponding double-trace instability onset. When the double-trace parameter satisfies $κ< κ_{\rm AdS}$, global AdS$_3$ becomes unstable and we identify its nonlinear endpoint as a zero-frequency boson star with energy below that of AdS$_3$, thereby providing the true ground state of the theory. In the microcanonical ensemble, hairy black holes always carry greater entropy than BTZ at fixed mass and angular momentum, and thus dominate whenever they exist. With notable exceptions, typically hairy black holes do not dominate the canonical nor the grand-canonical ensembles. We further show that, in the singular extremal limit, axisymmetric black holes saturate a generalised minimum-energy theorem under double-trace boundary conditions. These results yield the full nonlinear phase diagram of AdS$_3$ gravity with double-trace deformations.
format Preprint
id arxiv_https___arxiv_org_abs_2605_04145
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle When AdS$_3$ Grows Hair: Boson Stars, Black Holes, and Double-Trace Deformations
Dias, Oscar J. C.
Gil, David Sola
Santos, Jorge E.
High Energy Physics - Theory
General Relativity and Quantum Cosmology
We analyse three-dimensional Einstein gravity coupled to a massive complex scalar field with double-trace boundary conditions. Using high-precision spectral methods, we construct regular AdS$_3$ boson stars together with axisymmetric and non-axisymmetric hairy black holes. For each azimuthal number $m$, the hairy black holes bifurcate from the BTZ family at the corresponding double-trace instability onset. When the double-trace parameter satisfies $κ< κ_{\rm AdS}$, global AdS$_3$ becomes unstable and we identify its nonlinear endpoint as a zero-frequency boson star with energy below that of AdS$_3$, thereby providing the true ground state of the theory. In the microcanonical ensemble, hairy black holes always carry greater entropy than BTZ at fixed mass and angular momentum, and thus dominate whenever they exist. With notable exceptions, typically hairy black holes do not dominate the canonical nor the grand-canonical ensembles. We further show that, in the singular extremal limit, axisymmetric black holes saturate a generalised minimum-energy theorem under double-trace boundary conditions. These results yield the full nonlinear phase diagram of AdS$_3$ gravity with double-trace deformations.
title When AdS$_3$ Grows Hair: Boson Stars, Black Holes, and Double-Trace Deformations
topic High Energy Physics - Theory
General Relativity and Quantum Cosmology
url https://arxiv.org/abs/2605.04145