Space-time orbifold: A toy model for a cosmological singularity
Space-time orbifold: A toy model for a cosmological singularity
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, …