Atomic ionization by sterile-to-active neutrino conversion and constraints on dark matter sterile neutrinos with germanium detectors

TL;DR

This paper explores how sterile neutrinos could cause atomic ionization detectable by dark matter experiments, providing new constraints on their properties through germanium detector data.

Contribution

It introduces a novel inelastic scattering process for sterile neutrinos leading to atomic ionization, with potential experimental signatures and constraints.

Findings

Enhanced differential cross section at half the sterile neutrino mass

Constraints on sterile neutrino mass and magnetic moment from germanium detectors

Comparison with astrophysical bounds

Abstract

The transition magnetic moment of a sterile-to-active neutrino conversion gives rise to not only radiative decay of a sterile neutrino, but also its non-standard interaction (NSI) with matter. For sterile neutrinos of keV-mass as dark matter candidates, their decay signals are actively searched for in cosmic X-ray spectra. In this work, we consider the NSI that leads to atomic ionization, which can be detected by direct dark matter experiments. It is found that this inelastic scattering process for a nonrelativistic sterile neutrino has a pronounced enhancement in the differential cross section at energy transfer about half of its mass, manifesting experimentally as peaks in the measurable energy spectra. The enhancement effects gradually smear out as the sterile neutrino becomes relativistic. Using data taken with germanium detectors that have fine energy resolution in keV and sub-keV regimes, constraints on sterile neutrino mass and its transition magnetic moment are derived and compared with those from astrophysical observations.