Entanglement entropy in closed string theory

Author: Usman Naseer

Preprint number: UUITP-04/20

In local quantum field theory on a background spacetime, the entanglement entropy of a region is divergent due to the arbitrary short-wavelength correlations near the boundary of the region. Quantum gravitational fluctuations are expected to cut off the entropy of the ultraviolet modes. We study the entanglement entropy in closed string theory using the framework of string field theory. In particular, we compute the one-loop Renyi partition functions by considering the theory on a simple branched cover of the configuration space of closed strings. The short-wavelength modes are cut off at the string scale and the one-loop entanglement entropy is ultraviolet-finite. A non-canonical kinetic term in string field theory, required to produce the correct one-loop vacuum amplitude, plays a key role.