String Pair Production in a Time–Dependent Gravitational Field Andrew J. Tolley1, ∗ and Daniel H. Wesley1, † 1Joseph Henry Laboratories, Princeton University, Princeton NJ, 08544 (Dated: September 29, 2005) Abstract We study the pair creation of point–particles and strings in a time–dependent, weak gravitational field. We find that, for massive string states, there are surprising and significant differences between the string and point–particle results. Central to our approach is the fact that a weakly curved spacetime can be represented by a coherent state of gravitons, and therefore we employ standard techniques in string perturbation theory. String and point–particle pairs are created through tree– level interactions between the background gravitons. In particular, we focus on the production of excited string states and perform explicit calculations of the production of a set of string states of arbitrary excitation level. The differences between the string and point–particle results may contain important lessons for the pair production of strings in the strong gravitational fields of interest in cosmology and black hole physics. arXiv:hep-th/0509151v2 29 Sep 2005 ∗Electronic address:
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[email protected] 1 I. INTRODUCTION The aim of this paper is a calculation the pair production of strings in a time–dependent background. This phenomenon is of paramount importance in cosmology, particularly during (p)reheating after inflation, and near cosmological singularities. Usually one studies pair production using an effective field theory approach. Here we study a spacetime with weak gravitational fields and compute the pair production of excited string states using worldsheet methods.