Constraints on Brane Inflation and Cosmic Strings

TL;DR

This paper analyzes brane inflation models with cosmic strings, deriving constraints from WMAP data, and predicts that future Planck observations could further restrict string tension parameters, impacting inflationary theory.

Contribution

It provides the first detailed constraints on brane inflation parameters including cosmic strings using WMAP data, and forecasts the potential of Planck data to tighten these constraints.

Findings

Inclusion of cosmic strings is essential for constraining inflation models.

Models with a mass term predict very low tensor-to-scalar ratio r < 2*10^-5.

Planck data could rule out string tension Gμ > 6.5*10^-8.

Abstract

By considering simple, but representative, models of brane inflation from a single brane-antibrane pair in the slow roll regime, we provide constraints on the parameters of the theory imposed by measurements of the CMB anisotropies by WMAP including a cosmic string component. We find that inclusion of the string component is critical in constraining parameters. In the most general model studied, which includes an inflaton mass term, as well as the brane-antibrane attraction, values n_s < 1.02 are compatible with the data at 95 % confidence level. We are also able to constrain the volume of internal manifold (modulo factors dependent on the warp factor) and the value of the inflaton field to be less than 0.66M_P at horizon exit. We also investigate models with a mass term. These observational considerations suggest that such models have r < 2*10^-5, which can only be circumvented in the fast roll regime, or by increasing the number of antibranes. Such a value of r would not be detectable in CMB polarization experiment likely in the near future, but the B-mode signal from the cosmic strings could be detectable. We present forecasts of what a similar analysis using PLANCK data would yield and find that it should be possible to rule out G\mu > 6.5*10^-8 using just the TT, TE and EE power spectra.