caa a22 4500 445387068 CHVBK 20180317143035.0 cr unu---uuuuu 170323e20110401xx s 000 0 eng 10.1007/s10714-010-0994-4 doi (NATIONALLICENCE)springer-10.1007/s10714-010-0994-4 Signatures of the neutrino thermal history in the spectrum of primordial gravitational waves [Elektronische Daten] [Riccardo Benini, Massimiliano Lattanzi, Giovanni Montani] In this paper we study the effect of the anisotropic stress generated by neutrinos on the propagation of primordial cosmological gravitational waves. The presence of anisotropic stress, like the one generated by free-streaming neutrinos, partially absorbs the gravitational waves (GWs) propagating across the Universe. We find that in the standard case of three neutrino families, 22% of the intensity of the wave is absorbed, in fair agreement with previous studies. We have also calculated the maximum possible amount of damping, corresponding to the case of a flat Universe completely dominated by ultrarelativistic collisionless particles. In this case 43% of the intensity of the wave is absorbed. Finally, we have taken into account the effect of collisions, using a simple form for the collision term parameterized by the mean time between interactions, that allows to go smoothly from the case of a tightly coupled fluid to that of a collisionless gas. The dependence of the absorption on the neutrino energy density and on the effectiveness of the interactions opens the interesting possibility of observing spectral features related to particular events in the thermal history of the Universe, like neutrino decoupling and electron-positron annihilation, both occurring at T ~ 1 MeV. GWS entering the horizon at that time will have today a frequency ν ~ 10−9Hz, a region that is going to be probed by Pulsar Timing Arrays. Springer Science+Business Media, LLC, 2010 Gravitational waves nationallicence Neutrinos nationallicence Benini Riccardo ICRA and Physics Department, University of Rome, La Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy aut Lattanzi Massimiliano ICRA and Physics Department, University of Rome, La Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy aut Montani Giovanni ICRA and Physics Department, University of Rome, La Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy aut General Relativity and Gravitation Springer US; http://www.springer-ny.com 43/4(2011-04-01), 945-958 0001-7701 43:4<945 2011 43 10714 https://doi.org/10.1007/s10714-010-0994-4 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10714-010-0994-4 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Benini Riccardo ICRA and Physics Department, University of Rome, La Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy aut NATIONALLICENCE 700 1- Lattanzi Massimiliano ICRA and Physics Department, University of Rome, La Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy aut NATIONALLICENCE 700 1- Montani Giovanni ICRA and Physics Department, University of Rome, La Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy aut NATIONALLICENCE 773 0- General Relativity and Gravitation Springer US; http://www.springer-ny.com 43/4(2011-04-01), 945-958 0001-7701 43:4<945 2011 43 10714 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer