In this paper we study the effect of cosmic neutrino decoupling on the spectrum of cosmological gravitational waves (GWs). Before decoupling, namely at temperatures T ≫1 MeV, neutrinos constitute a perfect fluid and do not hinder GW propagation, while well after decoupling, for T ≪1 MeV, they free-stream generating an effective viscosity that damps cosmological GWs by a constant amount. In the intermediate regime, corresponding to the time of neutrino decoupling, the damping is frequency-dependent. GWs entering the horizon during neutrino decoupling have a frequency f ∼ 1 nHz; in particular, we show how neutrino decoupling induces a step in the spectrum of cosmological GWs just below 1 nHz, a frequency region that will be probed by Pulsar Timing Arrays (PTAs). We briefly discuss the conditions for a detection of this feature and conclude that it is unlikely to be observed by PTAs. © 2010 IOP Publishing Ltd.
|Publication status||Published - 2010|
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)