Brane inflation and the WMAP data: A Bayesian analysis
Sep, 2007
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Abstract: (arXiv)
The Wilkinson Microwave Anisotropy Probe (WMAP) constraints on string inspired ``brane inflation'' are investigated. Here, the inflaton field is interpreted as the distance between two branes placed in a flux-enriched background geometry and has a Dirac-Born-Infeld (DBI) kinetic term. Our method relies on an exact numerical integration of the inflationary power spectra coupled to a Markov-Chain Monte-Carlo exploration of the parameter space. This analysis is valid for any perturbative value of the string coupling constant and of the string length, and includes a phenomenological modelling of the reheating era to describe the post-inflationary evolution. It is found that the data favour a scenario where inflation stops by violation of the slow-roll conditions well before brane annihilation, rather than by tachyonic instability. Concerning the background geometry, it is established that log(v) > -10 at 95% confidence level (CL), where 'v' is the dimensionless ratio of the five-dimensional sub-manifold at the base of the six-dimensional warped conifold geometry to the volume of the unit five-sphere. The reheating energy scale remains poorly constrained, Treh > 20 GeV at 95% CL, for an extreme equation of state (wreh ~ -1/3) only. Assuming the string length is known, the favoured values of the string coupling and of the Ramond-Ramond total background charge appear to be correlated. Finally, the stochastic regime (without and with volume effects) is studied using a perturbative treatment of the Langevin equation. The validity of such an approximate scheme is discussed and shown to be too limited for a full characterisation of the quantum effects.Note:
- 70 pages, 19 figures, uses iopart
- 98.70.Vc
- 98.80.Cq
- inflation: stochastic
- membrane model: D-brane
- string model
- geometry: background
- Born-Infeld model
- cosmic background radiation
- power spectrum
- slow-roll approximation
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