Constraining Feeble Neutrino Interactions with Ultralight Dark Matter

TL;DR

This paper explores how ultralight bosonic dark matter interacting with neutrinos affects neutrino properties and cosmological observations, setting stringent limits on such interactions especially in the fuzzy dark matter regime.

Contribution

It provides a comprehensive cosmological analysis of neutrino-dark matter interactions and establishes new constraints on the coupling strength in the ultralight dark matter scenario.

Findings

Limits exclude couplings of order 10^{-30} for scalar masses around 10^{-20} eV.

Neutrino oscillations are affected by dark matter density, leading to observable consequences.

Constraints surpass those from time variation in scalar-induced couplings.

Abstract

If ultralight $(\ll$ 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 ($\sim 10^{-20}$ 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.