Relativistic D-brane Scattering is Extremely Inelastic

TL;DR

McAllister and Mitra demonstrate that ultrarelativistic Dp-brane collisions are dominated by copious production of highly excited open strings, with oscillator levels scaling as $\\propto \\eta^{2}$, which dramatically backreact on the brane trajectories and lead to rapid trapping in a symmetric configuration. They compute the interaction via the open-string annulus diagram, extract the imaginary part that governs open-string pair production, and show that the backreaction drives branes to stop within a stopping length of order $r_{*} \\\lesssim \\eta$ (in string units), with a substantial fraction of energy radiated as closed strings. The results reveal a purely stringy mechanism for extreme inelasticity that cannot be captured by low-energy EFT, with implications for cosmological models such as reheating in fast-brane scenarios and cyclic/ekpyrotic universes. Crucially, velocity-dependent corrections to open-string masses render highly excited string states light, enabling large-scale string production in fast brane collisions and driving the strong inelastic response observed.

Abstract

We study the effects of quantum production of open strings on the relativistic scattering of D-branes. We find strong corrections to the brane trajectory from copious production of highly-excited open strings, whose typical oscillator level is proportional to the square of the rapidity. In the corrected trajectory, the branes rapidly coincide and remain trapped in a configuration with enhanced symmetry. This is a purely stringy effect which makes relativistic brane collisions exceptionally inelastic. We trace this effect to velocity-dependent corrections to the open-string mass, which render open strings between relativistic D-branes surprisingly light. We observe that pair-creation of open strings could play an important role in cosmological scenarios in which branes approach each other at very high speeds.