2 research outputs found
Unconventional Cosmology
I review two cosmological paradigms which are alternative to the current
inflationary scenario. The first alternative is the "matter bounce", a
non-singular bouncing cosmology with a matter-dominated phase of contraction.
The second is an "emergent" scenario, which can be implemented in the context
of "string gas cosmology". I will compare these scenarios with the inflationary
one and demonstrate that all three lead to an approximately scale-invariant
spectrum of cosmological perturbations.Comment: 45 pages, 10 figures; invited lectures at the 6th Aegean Summer
School "Quantum Gravity and Quantum Cosmology", Chora, Naxos, Greece, Sept.
12 - 17 2012, to be publ. in the proceedings; these lecture notes form an
updated version of arXiv:1003.1745 and arXiv:1103.227
Cosmic Bounces and Cyclic Universes
Cosmological models involving a bounce from a contracting to an expanding
universe can address the standard cosmological puzzles and generate
"primordial" density perturbations without the need for inflation. Some such
models, in particular the ekpyrotic and cyclic models that we focus on, fit
rather naturally into string theory. We discuss a number of topics related to
these models: the reasoning that leads to the ekpyrotic phase, the predictions
for upcoming observations, the differences between singular and non-singular
models of the bounce as well as the predictive and explanatory power offered by
these models.Comment: 28 pages. Contribution to the CQG focus issue on String Cosmolog