  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}).

Astrophysics;High Energy Physics - Phenomenology