Constraints on brane inflation and cosmic strings

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 cosmic microwave background (CMB) anisotropies by WMAP (Wilkinson Microwave Anisotropy Probe) 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 the warped throat region (modulo factors dependent on the warp factor) and the value of the inflaton field to be < 0.66M(P) at horizon exit. We also investigate models with a mass term. These observational considerations suggest that such models have r < 2 x 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 any 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 x 10(-8) using just the TT, TE and EE power spectra.