Dark matter from neutrinos via enhanced cooling

It is widely accepted that all three species of neutrinos were in thermal equilibrium with the universe as it cooled to ~1 MeV/k, where k is Boltzmann’s constant. Further cooling of the decoupled neutrino sector occurred as the universe expanded. However, additional rapid cooling of the neutrino sector has no mechanism in the Standard Model. A modest extension of the Standard Model provides a means for rapid cooling of the neutrino sector to about m_ntc²/k where m_nt is the mass of the tau neutrino, via a family-specific form of SU(3). The interaction requires a density of neutrinos that is consistent with conditions in the early universe for significant cooling to occur. Properties of such an interaction lead to a dark matter content of the universe between 61% and 92%. The hypothesis yields neutrinos bound into states that are analogous to baryons with a mass of 0.4±0.2 eV/c². Pursuing the hypothesis results in a cool dissipationless state that is loosely bound near galaxies. A polytropic exponent near 2 gives a best fit to inferred galactic and cluster halo sizes and shapes, with best results utilizing a novel generalization of the equation of hydrostatic equilibrium. The Tremaine-Gunn bound is discussed.