Year: 2004
Type: article
Abstract: We analyze the general conditions on the equation of state w required for quantum fluctuations of a scalar field to produce a scale-invariant spectrum of density perturbations, including the possibility of models which (in the four dimensional effective description) bounce from a contracting to an expanding phase. We show that there are only two stable cases: $w\ensuremath{\approx}\ensuremath{-}1$ and $w\ensuremath{\gg}1.$ The first is utilized in inflationary models and the second in the ekpyrotic/cyclic scenario, assuming the perturbations propagate through the bounce. All other cases, including the $w\ensuremath{\approx}0$ case considered by some authors, require extreme fine-tuning of initial conditions and/or the effective potential. For the ekpyrotic/cyclic $(w\ensuremath{\gg}1)$ case, we also analyze the small deviations from scale invariance.
Institutions: Princeton University, Columbia University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2141293859