## Abstract

We consider a ℝ^{1,d}/ℤ_{2} orbifold, where ℤ_{2} acts by time and space reversal, also known as the embedding space of the elliptic de Sitter space. The background has two potentially dangerous problems: time-nonorientability and the existence of closed time-like curves. We first show that closed causal curves disappear after a proper definition of the time function. We then consider the one-loop vacuum expectation value of the stress tensor. A naive QFT analysis yields a divergent result. We then analyze the stress tensor in bosonic string theory, and find the same result as if the target space would be just the Minkowski space ℝ^{1,d}, suggesting a zero result for the superstring. This leads us to propose a proper reformulation of QFT, and recalculate the stress tensor. We find almost the same result as in Minkowski space, except for a potential divergence at the initial time slice of the orbifold, analogous to a spacelike Big Bang singularity. Finally, we argue that it is possible to define local S-matrices, even if the spacetime is globally time-nonorientable.

Original language | English (US) |
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Pages (from-to) | 1649-1679 |

Number of pages | 31 |

Journal | Journal of High Energy Physics |

Volume | 8 |

Issue number | 1 |

DOIs | |

State | Published - Jan 1 2004 |

## Keywords

- Bosonic Strings
- Discrete and Finite Symmetries
- Renormalization Regularization and Renormalons

## ASJC Scopus subject areas

- Nuclear and High Energy Physics