Abstract
The Standard Cosmological Model predicts the existence of relic neutrinos, which are indirectly probed through the effective number of relativistic species in the early Universe. In addition, from neutrino flavour oscillations we know that at least two of the neutrino mass states have a non-zero mass. Since the expansion of the Universe has diluted the energy of relic neutrinos, those that are massive are also non relativistic today. This means that they can be trapped in strong gravitational potentials, such as the one of the Milky Way. We review the calculation of the local overdensity of relic neutrinos produced from the gravitational attraction of our Galaxy, Andromeda and the Virgo cluster, commenting on the implications for an experiment aiming at relic neutrino detection, such as the PTOLEMY project.
Highlights
Current precision of most neutrino oscillation parameters is at the few per cent level
The standard model of cosmology, the so-called ΛCDM model, predicts that the current kinetic energy of relic neutrinos, which decoupled from the cosmic bath when the Universe was barely ∼ 1 s old, has diluted because of the cosmic expansion and average ∼ 0.17 meV, much smaller than the minimum required mass of the massive neutrino states
Relic neutrinos are by far the most common neutrinos in the Universe, not a single relic neutrino has been detected directly. We know of their existence in an indirect way from Neff, a cosmological parameter that accounts for all radiation at the early Universe that does not come from photons, and whose observed value [2] is compatible with the standard theoretical estimate Neff = 3.045 [3, 4, 5]
Summary
Current precision of most neutrino oscillation parameters is at the few per cent level. Since the relic neutrino capture event rate depends on the local number density of relic neutrinos, nν, , a key aspect in order to interpret adequately a future direct detection of these particles relies on knowing the exact overdensity that is due to gravitational attraction at our location in the Milky Way. 2.
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