http://arxiv.org/abs/2205.10516
We investigate polarized gravitational waves generated by chiral fermions in the early Universe. In particular, we focus on the contribution from left-handed neutrinos in thermal equilibrium with finite temperature and chemical potential in the radiation dominated era. We compute the correlation functions of gravitational fields pertinent to the Stokes parameter $V$ characterizing the circular polarization of gravitational waves in the Minkowski and expanding spacetime backgrounds. In the expanding universe, we find that the thermalized neutrinos induce a non-vanishing $V$ linear to the neutrino degeneracy parameter and wavenumber of gravitational waves in the long wavelength region. Possible future observations of such chiral gravitational waves could provide the information of the neutrino degeneracy parameter in the early Universe.
P. Gubler, N. Yamamoto and D. Yang
Tue, 24 May 22
54/92
Comments: 37 pages, 1 figure
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