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arXiv · 2609.34945

Black holes with axion hair from cubic Riemann interactions

Roberto Casadio·Roldao da Rocha
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Abstract

An effective field theory (EFT) of gravity with a cubic Riemann invariant coupled to an axion-like field is investigated and shown to propagate no additional independent low-energy degrees of freedom. This interaction generates a curvature-induced scalar profile around black holes, characterised by a secondary axion charge fixed by regularity of the axion field at the horizon, while the requirement of a regular event horizon constrains the asymptotic axion background. We construct the corresponding black hole solutions and show that the backreaction of the axion field could affect the metric only at subleading order in the EFT expansion. The modified geometry impacts black hole thermodynamics and Hawking evaporation, thus providing a controlled realisation of black holes with higher-curvature contributions and secondary axion hair motivated by ultraviolet physics. The modified Hawking temperature allows for the existence of black hole remnants at the end of the evaporation within the regime of validity of the EFT.

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Roberto Casadio, Roldao da Rocha. 2026-09-28. Black holes with axion hair from cubic Riemann interactions. https://arxiv.org/abs/2609.34945

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