Tensor modes from a primordial Hagedorn phase of string cosmology.
It has recently been shown that a Hagedorn phase of string gas cosmology can provide a causal mechanism for generating a nearly scale-invariant spectrum of scalar metric fluctuations, without the need for an intervening period of de Sitter expansion. In this Letter, we compute the spectrum of tensor metric fluctuations (gravitational waves) in this scenario and show that it is also nearly scale invariant. However, whereas the spectrum of scalar modes has a small red tilt, the spectrum of tensor modes has a small blue tilt, unlike what occurs in slow-roll inflation. This provides a possible observational way to distinguish between our cosmological scenario and conventional slow-roll inflation.
Brandenberger
Robert H
RH
Department of Physics, McGill University, Montréal QC, H3A 2T8, Canada. rhb@hep.physics.mcgill.ca
Nayeri
Ali
A
Patil
Subodh P
SP
Vafa
Cumrun
C