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arXiv · 2605.14132

Cosmological properties of black-hole hair in the linearly coupled scalar-Gauss-Bonnet theory

Dražen Glavan·Darío Jaramillo-Garrido
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Abstract

We investigate the superhorizon behavior of scalar hair sourced by black holes in de Sitter spacetime in the linearly coupled shift-symmetric scalar-Gauss-Bonnet theory. Working in the test-field regime, we show that this hair exhibits both temporal and spatial growth on superhorizon scales. This growth is not a special consequence of the black hole, but instead follows from the dynamics of a minimally coupled massless scalar field in expanding de Sitter spacetime. Moreover, it is not even specific to black holes, but also arises for a point scalar charge in de Sitter, indicating that a scalarized black hole acts effectively as a localized subhorizon source of scalar perturbations. Backreaction, when important, first arises on subhorizon scales and does not by itself eliminate the superhorizon profile. The time-dependent scalar hair also carries a steady outward energy flux, which frames the test-field regime as a transient, and helps explain the difficulties encountered in attempts to construct self-consistent static solutions.

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Dražen Glavan, Darío Jaramillo-Garrido. 2026-05-13. Cosmological properties of black-hole hair in the linearly coupled scalar-Gauss-Bonnet theory. https://doi.org/10.1103/q3nv-ccwn

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