Coherence Constraint on the Existence of Cosmic Defects

Abstract

We devise a measure n(r) to quantify a robust feature in the coherent cosmic perturbations, namely the narrowness of the first peak in the power spectrum of the Cosmic Microwave Background (CMB) anisotropy. A maximum-likelihood analysis using the WMAP data shows that the power fraction of any defect models at the first peak is persistently less than 4.5% at the 68% confidence. Our approach and results are insensitive to the uncertainties in the theoretical predictions for defect models, and thus the most robust to date. We show that to convert these results into realistic constraints on theories such as inflation, string cosmology, and SUSY GUTs, a more robust study for the cosmic-string-induced CMB around the degree scale is required.