Probing sub-eV Dark Matter decays with PTOLEMY

TL;DR

This paper explores the potential of the PTOLEMY experiment to detect sub-eV dark matter decays into neutrinos, which could reveal new dark radiation components and is sensitive to very long-lived dark matter particles.

Contribution

It provides a detailed forecast for detecting dark matter decays into neutrinos using PTOLEMY, highlighting the importance of spectral signatures and Pauli-blocking effects.

Findings

Dark matter decays with lifetimes up to 10^4 Gyr can be detected.

Distinct spectral features from neutrino dark radiation aid detection.

Detection is possible even with relaxed experimental performance requirements.

Abstract

When the Dark Matter mass is below the eV-scale, its cosmological occupation number exceeds the ones of photons from the cosmic microwave background as well as of relic neutrinos. If such Dark Matter decays to pairs of neutrinos, it implies that experiments that seek the detection of the cosmic neutrino background may as well be sensitive to this additional form of "dark radiation". Here we study the prospects for detection taking into account various options for the forecasted performance of the future PTOLEMY experiment. From a detailed profile likelihood analysis we find that Dark Matter decays with lifetime as large as $10^4$ Gyr or a sub-% Dark Matter fraction decaying today can be discovered. The prospects are facilitated by the distinct spectral event shape that is introduced from galactic and cosmological neutrino dark radiation fluxes. In the process we also clarify the importance of Pauli-blocking in the Dark Matter decay. The scenarios presented in this work can be considered early physics targets in the development of these instruments with relaxed demands on performance and energy resolution.