Signatures of Bulk Black Hole Merger from Semi-classical 2d CFT

We study the real-time bulk AdS$_3$ two-into-two scattering amplitude of conical defects. This is done through means of a previously developed method of systematic approximation of the monodromy problem for the Virasoro blocks of the four-point HHHH correlator in 2d CFT in the large central charge regime. We find that dialing the external scaling dimension triggers a transition from a scattering phase to an intermediate black hole phase. This transition occurs before the individual heavy operators exceed the BTZ mass gap.