Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2002-02-26
Phys.Rev. D67 (2003) 026003
Physics
High Energy Physics
High Energy Physics - Theory
21 pages, 2 figures
Scientific paper
10.1103/PhysRevD.67.026003
We explore bosonic strings and Type II superstrings in the simplest time dependent backgrounds, namely orbifolds of Minkowski space by time reversal and some spatial reflections. We show that there are no negative norm physical excitations. However, the contributions of negative norm virtual states to quantum loops do not cancel, showing that a ghost-free gauge cannot be chosen. The spectrum includes a twisted sector, with strings confined to a ``conical'' singularity which is localized in time. Since these localized strings are not visible to asymptotic observers, interesting issues arise regarding unitarity of the S-matrix for scattering of propagating states. The partition function of our model is modular invariant, and for the superstring, the zero momentum dilaton tadpole vanishes. Many of the issues we study will be generic to time-dependent cosmological backgrounds with singularities localized in time, and we derive some general lessons about quantizing strings on such spaces.
Balasubramanian Vijay
Hassan S. F.
Keski-Vakkuri Esko
Naqvi A. A.
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