Constraining Feeble Neutrino Interactions with Ultralight Dark Matter

Abstract

If ultralight ( eV), bosonic dark matter couples to right handed neutrinos, active neutrino masses and mixing angles depend on the ambient dark matter density. When the neutrino Majorana mass, induced by the dark matter background, is small compared to the Dirac mass, neutrinos are "pseudo-Dirac" fermions that undergo oscillations between nearly degenerate active and sterile states.We present a complete cosmological history for such a scenario and find severe limits from a variety of terrestrial and cosmological observables. For scalar masses in the "fuzzy" dark matter regime (∼ 10 −20 eV), these limits exclude couplings of order 10 −30 , corresponding to Yukawa interactions comparable to the gravitational force between neutrinos and surpassing equivalent limits on time variation in scalar-induced electron and proton couplings.

Cosmology-friendly time-varying neutrino masses via the sterile neutrino portal

“…An alternative scenario is the one in which right-handed neutrinos have no vacuum mass (m N = 0) but get a tiny Majorana mass from their coupling to the scalar field. This can give rise to ultralight scalar-induced Pseudo-Dirac neutrinos [67]. The framework explored in this work is different from the earlier discussions about the mass-varying neutrinos, where the tiny neutrino mass is hypothetically generated from the coupling to the dark energy (e.g., acceleron [38], quintessence, etc.).…”