Extremal Love: tidal/electromagnetic deformability, logarithmic running and the weak gravity conjecture

In General Relativity, the tidal Love numbers of black holes vanish, implying they are resistant to tidal deformation. This “rigidity” is easily broken in the presence of higher-derivative corrections. Focusing on extremal charged black holes in Einstein-Maxwell EFT, we compute the static linear response for both the vector ($\ell=1$) and parity-odd tensor ($\ell \ge 2$) sectors. We find that the resulting tidal Love numbers are non-zero and exhibit logarithmic running, a hallmark of quantum corrections. Crucially, we show that the sign of these deformations is not arbitrary; the induced electric and magnetic susceptibilities and their log runnings in the $\ell=1$ sector are constrained by unitarity and the Weak Gravity Conjecture. Furthermore, due to gravito-electromagnetic mixing, we find the cross log runnings and show that they are the same, which we explain through the worldline effective field theory.

💡 Research Summary

The paper investigates how higher‑derivative corrections in an Einstein‑Maxwell effective field theory (EFT) modify the tidal response of extremal charged black holes. In pure General Relativity the static tidal Love numbers (TLNs) of four‑dimensional black holes vanish, reflecting a “rigidity” that mirrors no‑hair theorems. The authors augment the Einstein‑Maxwell action with the leading four‑derivative operators
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