In this paper we study the effect of cosmic neutrino decoupling on the spectrum of cosmological gravitational waves (GWs). At temperatures T ≫ 1MeV, neutrinos constitute a perfect fluid and do not hinder GW propagation, while for T ≪ 1MeV they free-stream and have an effective viscosity that damps cosmological GWs by a constant amount. In the intermediate regime, corresponding to neutrino decoupling, the damping is frequency dependent. GWs entering the horizon during neutrino decoupling have a frequency f ∼ 1 nHz, corresponding to a frequency region that will be probed by pulsar timing arrays (PTAs). In particular, we show how neutrino decoupling induces a spectral feature in the spectrum of cosmological GWs just below 1 nHz. We briefly discuss the conditions for detection of this feature and conclude that it is unlikely to be observed by PTAs. © 2010 IOP Publishing Ltd.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)
Lattanzi, M., Benini, R., & Montani, G. (2010). A possible signature of cosmic neutrino decoupling in the nHz region of the spectrum of primordial gravitational waves. Classical and Quantum Gravity, 27(19), -. . https://doi.org/10.1088/0264-9381/27/19/194008