Limits on Defects Formation and Hybrid Inflationary Models with Three-Year WMAP Observations

We confront the predicted effects of hybrid inflationary models on the Cosmic Microwave Background (CMB) with three years of Wilkinson Microwave Anisotropy Probe (WMAP) observations. Using model selection, we compare the ability of a simple flat power-law LCDM model to describe the data to that of hybrid inflationary models involving global or local cosmic strings, or global textures. We find that it is statistically impossible to distinguish between these models: they all give a similar description of the data, the maximum ratio of the various Bayesian evidences involved being never higher than e^{0.1 \pm 0.5}. We then derive the maximum contribution that topological defects can make to the CMB, and place an upper bound on the possible value of cosmic strings' tension of G\mu \leq 2.1 \times 10^{-7} (68% confidence limit). Finally, we give the corresponding constraints on the D-term strings' mass scale, as well as limits on the F- and D-term coupling constants (\kappa and \lambda) and inflationary scales (M and \sqrt{\xi}).