Constraints on Topological Defects Energy Density from First-Year WMAP Results

We compare the predictions of hybrid inflationary models that produce both adiabatic fluctuations and topological defects to first year WMAP results. We use a Markov Chain Monte Carlo method to constrain the contribution of cosmic strings and textures to the CMB angular power spectrum. Marginalizing this contribution over the cosmological parameters of a power law flat LCDM model, we place a 95% upper limit of 23% on the topological defects contribution to density fluctuations, the maximum likelihood being of order 4%. This corresponds to an upper limit on the string scale of G\mu \leq 3.2 \times 10^{-7}. We also explore the degeneracies between the defects contribution and other cosmological parameters.