Light neutrinophilic WIMP in the $U(1)_{\rm B-L+xY}$ model

TL;DR

This paper proposes a neutrinophilic $U(1)_{B-L+xY}$ gauge symmetry model for sub-GeV dark matter, enabling thermal freeze-out with predominantly neutrino annihilation, compatible with current constraints and possibly addressing small-scale structure issues.

Contribution

It introduces a novel $U(1)_{B-L+xY}$ gauge symmetry framework for sub-GeV dark matter, emphasizing neutrino interactions and viability under existing experimental and cosmological constraints.

Findings

Viable parameter space for sub-GeV dark matter with thermal relic abundance.

Dark matter predominantly annihilates into neutrinos, avoiding CMB constraints.

Potential for dark matter self-interactions to address small-scale structure problems.

Abstract

Sub-GeV dark matter is an appealing thermal target because it can still be produced via the standard freeze-out mechanism; at such low masses, achieving freeze-out naturally points to the presence of a light mediator, which shifts the most promising discovery avenues from the energy frontier to the intensity frontier. Realizing this picture is nonetheless challenging, since CMB observations tightly constrain energy injection from dark-matter annihilation at recombination and therefore strongly disfavor simple $s$-wave annihilation into visible Standard-Model final states. In this work, we propose a concrete neutrinophilic framework for sub-GeV thermal dark matter (''light WIMPs'') based on an additional gauge symmetry $\mathrm{U}(1)_{\mathrm{B}-\mathrm{L}+x\mathrm{Y}}$; for an appropriate choice of $x$, the new gauge boson couples predominantly to dark matter and neutrinos while its couplings to charged leptons are suppressed, so that sub-GeV dark matter annihilates almost exclusively into neutrinos, with hadronic modes kinematically closed. We map the parameter space in which the observed relic abundance is reproduced via standard thermal freeze-out in a conventional cosmological history, and show that sizable regions remain viable after imposing current cosmological, indirect-detection, and terrestrial constraints; in part of the allowed parameter space, the dark matter also exhibits sufficiently large self-interactions to potentially alleviate small-scale structure tensions.