Calculation of the local density of relic neutrinos

Abstract

Abstract. Nonzero neutrino masses are required by the existence of flavour oscillations, with values of the order of at least 50 meV. We consider the gravitational clustering of relic neutrinos within the Milky Way, and used the N -one-body simulation technique to compute their density enhancement factor in the neighbourhood of the Earth with respect to the average cosmic density. Compared to previous similar studies, we pushed the simulation down to smaller neutrino masses, and included an improved treatment of the baryonic and dark matter distributions in the Milky Way. Our results are important for future experiments aiming at detecting the cosmic neutrino background, such as the Princeton Tritium Observatory for Light, Early-universe, Massive-neutrino Yield (PTOLEMY) proposal. We calculate the impact of neutrino clustering in the Milky Way on the expected event rate for a PTOLEMY-like experiment. We find that the effect of clustering remains negligible for the minimal normal hierarchy scenario, while it enhances the event rate by 10 to 20% (resp. a factor 1.7 to 2.5) for the minimal inverted hierarchy scenario (resp. a degenerate scenario with 150 meV masses). Finally we compute the impact on the event rate of a possible fourth sterile neutrino with a mass of 1.3 eV.

Neutrino clustering in the Milky Way and beyond

“…The larger clustering is likely due to our updated dark matter profile parameters. Our results are even closer to those of [18,19], although slightly smaller in the NFW case (due to different assumptions on the NFW parameters), both for the dark matter only case and for the case with baryonic contributions.…”

“…we only consider dark matter with an NFW profile. We also compare our results with those of previous studies [17][18][19].…”

“…The latter case consists in computing the trajectories of several (N ) independent test particles (one-body) in the evolving gravitational potential of the Galaxy, starting from some high redshift until today, and then reconstructing the profile of the neutrino halo according to the final positions of all the test particles. The same method has been adopted later in [18,19], where an updated treatment of the dark matter (DM) and baryonic content of the Milky Way was considered.…”

“…In this paper, we improve the calculation presented in [18]. For the first time, we take into account not only the contribution of the Milky Way, but also the contribution of relevant, nearby astrophysical objects, such as the Andromeda galaxy and the Virgo cluster.…”

“…Einasto M vir [M ] 2.03 × 10 12 1.17 × 10 12 ρ 0 [M /kpc 3 ] 1.06 × 10 72.70 × 10 8 R Dark matter density parameters for the Milky Way at z = 0, obtained by fitting the data from[31], following the same procedure as in[18].…”