Extremal Love: tidal/electromagnetic deformability, logarithmic running and the weak gravity conjecture
arXiv:2601.20962 · doi:10.1007/JHEP08(2026)033
Abstract
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 () and parity-odd tensor () 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 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.
35 pages, published version
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