Late-phase-transition-induced fluctuations in the cosmic neutrino distribution and the formation of structure in the Universe.

Abstract

We show that late-time (${T}_{c}\ensuremath{\le}1$ eV) cosmic vacuum phase transitions which induce separation of phases and which involve a discontinuity in neutrino properties (e.g., mass) across phase boundaries could give rise to spatial inhomogeneities in the distribution of neutrinos. The nucleation physics of the phase transition would determine the spatial scale of the fluctuations. These density perturbations would be born in the nonlinear regime and could have masses in the range of ${10}^{6}{M}_{\ensuremath{\bigodot}}\ensuremath{-}{10}^{13}{M}_{\ensuremath{\bigodot}}$. If the fluctuations are shells, as expected, and there is gravitational modification of the original phasetransition nucleation scale then the upper limit on their masses could be considerably larger ($\ensuremath{\approx}{10}^{18}{M}_{\ensuremath{\bigodot}}$), possibly encompassing the largest structures in the Universe. The motivation for this work stems, in part, from the possibility that future experiments (i.e., solar neutrino experiments) may suggest new, low-energy-scale weak-interaction phenomena, such as neutrino flavor mixing.