Coarse-graining in time, emergent temperature in 2d CFT at large central charge

Abstract

Using the monodromy method, a compact expression is obtained for the identity block contribution to the expectation value of two low-energy probe operators on a broad class of time-dependent heavy pure states in large-$c$ 2d CFTs. It will be shown that the size of the compact spatial dimension sets a coarse-graining time-scale above which the thermal two-point function naturally emerges. A phenomena will be highlighted where the information of the pure state appears to get projected down to a single conformal representation. We will see that this projection is corroborated by known conformal bootstrap results.