Comparing Brane Inflation to WMAP

TL;DR

This paper evaluates a brane inflation model against recent cosmological data, exploring its compatibility and potential stringy signatures like large tensor modes and non-Gaussianity.

Contribution

It compares the simplest brane inflation model with observational data, analyzing both slow-roll and relativistic scenarios within string theory constraints.

Findings

Constraints on model parameters from WMAP, SDSS, and SNLS data.

Potential for large tensor modes and non-Gaussianity as stringy signatures.

Deviations from standard slow-roll predictions in the tensor mode properties.

Abstract

We compare the simplest realistic brane inflationary model to recent cosmological data, including WMAP 3-year cosmic microwave background (CMB) results, Sloan Digital Sky Survey luminous red galaxies (SDSS LRG) power spectrum data and Supernovae Legacy Survey (SNLS) Type 1a supernovae distance measures. Here, the inflaton is simply the position of a $D3$-brane which is moving towards a $\bar{D}3$-brane sitting at the bottom of a throat (a warped, deformed conifold) in the flux compactified bulk in Type IIB string theory. The analysis includes both the usual slow-roll scenario and the Dirac-Born-Infeld scenario of slow but relativistic rolling. Requiring that the throat is inside the bulk greatly restricts the allowed parameter space. We discuss possible scenarios in which large tensor mode and/or non-Gaussianity may emerge. Here, the properties of a large tensor mode deviate from that in the usual slow-roll scenario, providing a possible stringy signature. Overall, within the brane inflationary scenario, the cosmological data is providing information about the properties of the compactification of the extra dimensions.