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arXiv · 1902.05760

Spontaneous scalarization of charged black holes at the approach to extremality

Yves Brihaye·Betti Hartmann
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Abstract

We study static, spherically symmetric and electrically charged black hole solutions in a quadratic Einstein-scalar-Gauss-Bonnet gravity model. Very similar to the uncharged case, black holes undergo spontaneous scalarization for sufficiently large scalar-tensor coupling $\gamma$ - a phenomenon attributed to a tachyonic instability of the scalar field system. While in the uncharged case, this effect is only possible for positive values of $\gamma$, we show that for sufficiently large values of the electric charge $Q$ two independent domains of existence in the $\gamma$-$Q$-plane appear: one for positive $\gamma$ and one for negative $\gamma$. We demonstrate that this new domain for negative $\gamma$ exists because of the fact that the near-horizon geometry of a nearly extremally charged black hole is $AdS_2\times S^2$.This new domain appears for electric charges larger than approximately 74$\%$ of the extremal charge. For positive $\gamma$ we observe that a singularity with diverging curvature invariants forms outside the horizon when approaching extremality.

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Yves Brihaye, Betti Hartmann. 2019-02-15. Spontaneous scalarization of charged black holes at the approach to extremality. https://doi.org/10.1016/j.physletb.2019.03.043

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