Abstract
In recent work, two of us proposed a nonsingular Ekpyrotic cosmology making use of an S-brane which forms at the end of the phase of Ekpyrotic contraction. This S-Brane mediates a transition between contraction and expansion. Graviitational waves passing through the S-Brane acquire a roughly scale-invariant spectrum, and if the S-Brane has zero shear, then a roughly scale-invariant spectrum of cosmological perturbatiions results. Here, we study the production of gauge field fluctuations driven by the decay of the S-Brane, and we show that the reheating process via gauge field production will be efficient, leading to a radiation-dominated expanding phase.
Highlights
The inflationary scenario [1] has become the standard paradigm of early universe cosmology, it has recently been challenged from considerations based on fundamental physics
The effective field theory description of inflation is subject to the trans-Planckian censorship constraint (TCC) [4] which forces the energy scale of inflation to be many orders of magnitude smaller than the scale of particle physics grand unification, leading to a negligible amplitude of primordial gravitational waves [5]
We have studied the embedding of the S-brane bounce scenario proposed in [17] into string theory
Summary
The inflationary scenario [1] has become the standard paradigm of early universe cosmology, it has recently been challenged from considerations based on fundamental physics. The ekpyrotic scenario is based on the hypothesis that the contracting phase was one of very slow contraction Such a phase can be realized in the context of Einstein gravity by assuming that matter is dominated by a scalar field φ with a negative exponential potential (but positive total energy density) such that the equation of state is w ≫ 1, where w 1⁄4 P=ρ is the ratio between pressure P and energy density ρ. String theory, the S-brane represents string degrees of freedom which decouple at low energy densities but become comparable in energy to the energy scale of the background and have to be included in the low energy effective field theory as a space-filling object which is localized at a fixed time Such a brane has vanishing energy density, and negative pressure (positive tension). The reduced Planck mass is denoted by mpl and it is related to Newton’s gravitational constant G via m−pl2 1⁄4 8πG
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