Massive string modes and non-singular pre-big-bang cosmology

Abstract

Perturbative ${\alpha }^{\prime }$ corrections to the low energy string effective action have been recently found to have a potentially regularizing effect on the singularity of the lowest order pre-big-bang solutions. Whether they actually regularize it, however, cannot be determined working at any finite order in a perturbative expansion in powers of the string constant ${\alpha }^{\prime }$, because of scheme dependence ambiguities. Physically, these corrections are dominated by the integration over the first few massive string states. Very massive string modes, instead, can have a regularizing effect which is non-perturbative in ${\alpha }^{\prime }$ and which basically comes from the fact that in a gravitational field with Hubble constant $H$ they are produced with an effective Hawking temperature $T=H/(2\pi )$, and an infinite production rate would occur if this temperature exceeded the Hagedorn temperature. We discuss technical and conceptual difficulties of this non-perturbative regularization mechanism.

25 pages, Latex, 3 figures. Conceptual revisions. To be published in Nucl. Phys. B

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• Duality and Dilaton
• A Model of Graceful Exit in String Cosmology
• Duality Beyond the First Loop
• Graceful Exit and Energy Conditions in String Cosmology
• Expanding and contracting universes in third quantized string cosmology

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