How to recover unitarity in gravitational high-energy scattering of particles and strings on Dp-branes
OKC/Nordita High-Energy Physics Theory seminar
Monday 20 January 2014
to 15:00 at
Paolo Di Vecchia (Nordita)
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.