Signatures of Dark Radiation in Neutrino and Dark Matter Detectors

TL;DR

This paper explores how late-decaying dark radiation, possibly from dark matter, can leave detectable signals in neutrino and dark matter detectors, providing new constraints and insights into non-standard neutrino sources.

Contribution

It introduces a framework for constraining late-time dark radiation interactions using direct detection experiments, highlighting the impact of non-standard neutrino sources on detection limits.

Findings

Constraints on dark radiation from neutrino and dark matter experiments.

Interacting dark radiation with ~30 MeV/c momentum is detectable.

Dark matter decay can produce a neutrino floor closer to current bounds.

Abstract

We consider the generic possibility that the Universe's energy budget includes some form of relativistic or semi-relativistic dark radiation (DR) with non-gravitational interactions with Standard Model (SM) particles. Such dark radiation may consist of SM singlets or a non-thermal, energetic component of neutrinos. If such DR is created at a relatively recent epoch, it can carry sufficient energy to leave a detectable imprint in experiments designed to search for very weakly interacting particles: dark matter and underground neutrino experiments. We analyze this possibility in some generality, assuming that the interactive dark radiation is sourced by late decays of an unstable particle, potentially a component of dark matter, and considering a variety of possible interactions between the dark radiation and SM particles. Concentrating on the sub-GeV energy region, we derive constraints on different forms of DR using the results of the most sensitive neutrino and dark matter direct detection experiments. In particular, for interacting dark radiation carrying a typical momentum of $\sim30$~MeV$/c$, both types of experiments provide competitive constraints. This study also demonstrates that non-standard sources of neutrino emission (e.g. via dark matter decay) are capable of creating a "neutrino floor" for dark matter direct detection that is closer to current bounds than is expected from standard neutrino sources.