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.

A possible signature of cosmic neutrino decoupling in the nHz region of the spectrum of primordial gravitational waves

M. Lattanzi
Primo
;
2010

Abstract

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
Lattanzi, M.; Benini, R.; Montani, G.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2279694
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