Glimpses of black hole formation/evaporation in highly inelastic, ultra-planckian string collisions

Abstract

We revisit possible glimpses of black-hole formation by looking at ultra-planckian string-string collisions at very high final-state multiplicity. We compare, in particular, previous results using the optical theorem, the resummation of ladder diagrams at arbitrary loop order, and the AGK cutting rules, with the more recent study of $2 \rightarrow N$ scattering at $N \sim s M_P^{-2} \gg 1$. We argue that some apparent tension between the two approaches disappears once a reinterpretation of the latter's results in terms of suitably defined infrared-safe cross sections is adopted. Under that assumption, the typical final state produced in an ultra-planckian collision does indeed appear to share some properties with those expected from the evaporation of a black hole of mass $\sqrt{s}$, although no sign of thermalization is seen to emerge at this level of approximation.