Yi-Fu Cai, Evan McDonough, Francis Duplessis, Robert Brandenberger
We reconsider the non-singular Matter Bounce scenario first developed in [arXiv:1206.2382] which starts with a matter-dominated period of contraction and transitions into an Ekpyrotic phase of contraction. We consider consistently both matter fields, the first of which plays the role of regular matter, and the second of which is responsible (via the choice of its potential) for a period of Ekpyrotic contraction, and (via Galileon type kinetic operators) for the nonsingular bounce. Since the dominant matter field is massive, the induced curvature fluctuations are initially not scale-invariant, whereas the fluctuations of the second scalar field (which are initially entropy fluctuations) are scale-invariant. We study the transfer of the initial entropy perturbations into curvature fluctuations in the matter-dominated phase of contraction and show that the latter become nearly scale invariant on large scales but are blue tilted on small scales, which may provide a distinct signature for forthcoming observations. The existence of a second field leads to the generation of entropy perturbations. We study the evolution of both curvature and entropy fluctuations through the bounce. We show that both have a scale-invariant spectrum which is blue-tilted on small scales, but that the entropy fluctuations end up with an amplitude which in general is much smaller than that of the curvature perturbations since curvature perturbations undergo a gravitational amplification during the bounce phase. Therefore, our model predicts that the universe is highly adiabatic and isotropic after the bounce even after the addition of regular matter and hence provides a paradigm competitive to inflation for explaining the origin of structure in the universe.
View original:
http://arxiv.org/abs/1305.5259
No comments:
Post a Comment