Theoretical constraints on brane inflation and cosmic superstring radiation

Abstract

We analyze theoretical constraints on the radiation modes of cosmic superstrings. Given that cosmic superstrings are formed at the end of brane inflation, we first investigate the implications of recently elucidated supergravity constraints on brane inflation models. We show that both D3/D7 and ${{{{\text{D}}3}} \left/ {{\overline {{\text{D}}3} }} \right.}$ brane inflation are subject to non-trivial constraints. Both inflationary models can be shown to satisfy those constraints, but for the case of D3/D7 there seem to be important consequences for the dynamics of the inflationary mechanism. Bearing this in mind, we analyze the theoretical constraints on the nature of the allowed radiation by cosmic superstrings in the context of a warped background where brane-antibrane inflation takes place. Clearly such constraints do not apply to field theoretic cosmic strings, or to cosmic strings that arise in a background without warping. We argue that in a warped background where one might expect axionic radiation to be enhanced relative to gravitational radiation, neither F-strings nor D-strings can emit axionic radiation, and FD-strings cannot give rise to Neveu-Schwarz-Neveu-Schwarz particle emission, while their Ramond-Ramond particle emission is not well-defined.