Investigation of the Cosmic evolution in the presence of non-relativistic neutrinos

Abstract

Abstract The neutrinos of the early universe evolved from a relativistic phase at very early times to a massive particle behavior at later times. First, the kinetic energy of neutrinos is relativistic, and as a result, neutrinos can be described as massless particles. As the Universe expands, the temperature drops and the kinetic energy decreases, and the neutrinos turn into a non-relativistic phase with a non-negligible mass. In this paper, we first put constraints on the total mass of neutrinos. Then we investigate the effect of neutrinos on the CMB power spectrum, P(k), in the case of massless and massive neutrinos using the publicly available Boltzmann code CAMB and we prove that when neutrino coupled to scalar field the CMB power spectrum has a little shift, which means that the power spectrum of CMB is greatly affected by the background energy density and the accelerated expansion of the Universe. Furthermore, we investigate the effect of perturbed quintessence on this spectrum and find that the highest peaks of this spectrum are shifted to smaller scales. Also, we estimate the Deceleration–Acceleration(DA) redshift transition (z da) using the coupling canonical scalar field with neutrinos. For Pantheon data we obtain z da = 0.7 ± 0.05 and for CC data z da = 0.68 ± 0.03. In the presence of neutrinos the DA redshift transition is z da = 0.42 ± 0.03 for Pantheon data and z da = 0.49 ± 0.05 for CC data. These results indicate that neutrinos can affect this phase transition. The results obtained in this article show that when the mass of neutrinos increases, the value of the background energy density increases, resulting in a higher power spectrum peak. Also, by examining the effect of coupling neutrinos to dark energy, we find that the transition occurs at lower redshift.