Constraints on brane inflation and cosmic strings

Abstract

By considering simple, but representative, models of brane inflation from a singlebrane–antibrane pair in the slow roll regime, we provide constraints on the parametersof the theory imposed by measurements of the cosmic microwave background(CMB) anisotropies by WMAP (Wilkinson Microwave Anisotropy Probe) includinga cosmic string component. We find that inclusion of the string component iscritical in constraining parameters. In the most general model studied, whichincludes an inflaton mass term, as well as the brane–antibrane attraction, valuesns<1.02 are compatiblewith 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<0.66MP at horizon exit. We also investigate models with a mass term.These observational considerations suggest that such models haver<2 × 10−5, whichcan only be circumvented in the fast roll regime, or by increasing the number of antibranes. Such a valueof r would not be detectable in any CMB polarization experiment likely in the near future, but theB-mode signal from the cosmic strings could be detectable. We present forecasts of what a similaranalysis using PLANCK data would yield and find that it should be possible to rule outGμ>6.5 × 10−8 usingjust the TT, TE and EE power spectra.