Lightcone Modular Bootstrap and Tauberian Theory: A Cardy-Like Formula for Near-Extremal Black Holes

Abstract

AbstractWe show that for a unitary modular invariant 2D CFT with central charge $$c>1$$ c > 1 and having a nonzero twist gap in the spectrum of Virasoro primaries, for sufficiently large spin J, there always exist spin-J operators with twist falling in the interval $$(\frac{c-1}{12}-\varepsilon ,\frac{c-1}{12}+\varepsilon )$$ ( c - 1 12 - ε , c - 1 12 + ε ) with $$\varepsilon =O(J^{-1/2}\log J)$$ ε = O ( J - 1 / 2 log J ) . We establish that the number of Virasoro primary operators in such a window has a Cardy-like, i.e., $$\exp \left( 2\pi \sqrt{\frac{(c-1)J}{6}}\right) $$ exp 2 π ( c - 1 ) J 6 growth. A similar result is proven for a family of holographic CFTs with the twist gap growing linearly in c and a uniform boundedness condition, in the regime $$J\gg c^3\gg 1$$ J ≫ c 3 ≫ 1 . From the perspective of near-extremal rotating BTZ black holes (without electric charge), our result is valid when the Hawking temperature is much lower than the “gap temperature.”