1207.6266 (Joanes Lizarraga et al.)

Correlations between cosmic strings and extra relativistic species    [PDF]

Joanes Lizarraga, Irene Sendra, Jon Urrestilla

The recent observation that the Cosmic Microwave Background (CMB) prefers a neutrino excess has triggered a number of works studying this possibility. The effect obtained by the non-interacting massless neutrino excess could be mimicked by some extra radiation component in the early universe, such as a cosmological gravitational wave background. Prompted by the fact that a possible candidate to source those gravitational waves would be cosmic strings, we perform a parameter fitting study with models which considers both cosmic strings and the effective number of neutrinos as free parameters, using CMB and non-CMB data. The implications are twofold: on the one hand cosmic strings may be the extra source of the gravity wave background needed to fit the data; and on the other, due to correlations between parameters, a lower extra radiation component may be needed. We find that there is in fact a correlation between cosmic strings and the number of extra relativistic species, and that strings account for at least a part of the extra radiation necessary, but it depends strongly on the cosmological data used. In fact, CMB data prefer strings at a 2sigma level, paying the price of a higher extra radiation component. CMB data also give a moderate preference for a model with ns=1. The inclusion of non-CMB data lowers both the preference for strings and for the extra relativistic species.

View original: http://arxiv.org/abs/1207.6266