Free partition functions and an averaged holographic duality

We study the torus partition functions of free bosonic CFTs in two dimensions. Integrating over Narain moduli defines an ensemble-averaged free CFT. We calculate the averaged partition function and show that it can be reinterpreted as a sum over topologies in three dimensions. This result leads us to conjecture that an averaged free CFT in two dimensions is holographically dual to an exotic theory of three-dimensional gravity with U(1)(c)xU(1)(c) symmetry and a composite boundary graviton. Additionally, for small central charge c, we obtain general constraints on the spectral gap of free CFTs using the spinning modular bootstrap, construct examples of Narain compactifications with a large gap, and find an analytic bootstrap functional corresponding to a single self-dual boson.

Automated summary

The study focuses on the torus partition functions of free bosonic CFTs in two dimensions, showing that integrating over Narain moduli defines an ensemble-averaged free CFT and the averaged partition function can be reinterpreted as a sum over topologies in three dimensions. This leads to the conjecture that an averaged free CFT in two dimensions is holographically dual to an exotic theory of three-dimensional gravity with U(1)(c)xU(1)(c) symmetry and a composite boundary graviton. Additionally, general constraints on the spectral gap of free CFTs are obtained for small central charge c, Narain compactifications with a large gap are constructed, and an analytic bootstrap functional corresponding to a single self-dual boson is found using the spinning modular bootstrap.