How to recover unitarity in gravitational high-energy scattering of particles and strings on Dp-branes

by Paolo Di Vecchia (Nordita)

Monday 20 Jan 2014, 13:30 → 15:00 Europe/Stockholm

122:026

High-energy scattering in a gravitational theory is dominated by graviton exchanges. Since gravitons are coupled to energy, perturbative unitarity is violated. In this talk we will discuss how unitarity is recovered in the scattering of both a particle and a closed string on D-branes. In the case of a particle one must re-sum the perturbative series getting the eikonal c-number phase that is unitary. The case of string is more interesting because one gets the eikonal operator that is an operator in the Hilbert space of the string states. In this case, unlike the scattering of a particle, elastic unitarity is violated and, in order to recover the full unitarity, one must include inelastic processes. For a large number N of parallel D-branes, we can neglect multi closed-string production from the scattering of a closed string on N D-branes. In this talk the eikonal operator is obtained with a complete string calculation. This allows us to identify the microscopic closed-string states that must be included for satisfying the unitarity requirement for large impact parameter. At the end of the talk we will discuss the lack of unitarity occurring at smaller impact parameters due to the fact that the production of open strings has not been properly taken into account.