ABSTRACT
In the previous chapter, we discussed the gravitational instability scenario in a universe composed only of photons and baryons. We neglected on purpose an explicit discussion about the Cosmic Neutrino Background (CνB). The reason was that massless neutrinos redistribute themselves homogeneously at each time t over the horizon scale and then de facto do not participate in the gravitational instability process on small scales. Things change completely if we assume that neutrinos have non-zero rest masses. This possibility was taken seriously after the claim by Lyubimov et al. [133] in 1980 that the electron antineutrino rest mass was m ν ¯ e = ( 30 ± 15 ) e V https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315181394/3da2550c-66ec-43f3-abaf-ee4e79cf2377/content/eq1031.tif"/> . Although we know today that m ν ¯ e < 2.3 e V https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315181394/3da2550c-66ec-43f3-abaf-ee4e79cf2377/content/eq1032.tif"/> at the 95% confidence level [113], the importance of the Lyubimov et al. paper was to lend credibility to the theoretical predictions about the impact of massive neutrinos in cosmology and to open a new bridge to particle physics on the issue of the large-scale structure formation in the universe.
