Atomic ionization by sterile-to-active neutrino conversion and constraints on dark matter sterile neutrinos with germanium detectors
Jiunn-Wei Chen1, Hsin-Chang Chi2, Cheng-Pang Liu2, Lakhwinder Singh3,4, Shih-Ted Lin3, Henry T. Wong3, Chih-Pan Wu1,3*, Chih-Liang Wu1,3
1Department of Physics, National Taiwan University, Taipei City, Taiwan
2Department of Physics, National Dong Hwa University, Hualien, Taiwan
3Institute of Physics, Academia Sinica, Taipei City, Taiwan
4Department of Physics, Banaras Hindu University, Varanasi, India
* presenting author:Chih-Pan Wu,
Sterile neutrinos are invoked in many beyond-the-Standard-Model theories, in addition to the three known active neutrinos, to address fundamental questions including explaining the origin of neutrino masses, providing suitable dark matter candidates, and setting the stage of leptogenesis that subsequently leads to the baryon asymmetry of the universe.
Recently there are two groups reporting abnormal X-ray emission lines at around E = 3.55 keV. These results triggered a possibility of a decaying sterile neutrino with mass ms = 7.1 keV. Motivated by this anomalous X-ray emission line and its possible interpretation of radiative sterile neutrino decay, we consider an effective Lagrangian that gives rise to the coupling of an incoming sterile neutrino, an outgoing active (light) neutrino, and a virtual photon. When the virtual photon couples to electromagnetic currents of normal matter, this will generate some signals which can be searched for with typical direct dark matter detectors.
The specific process we study is atomic ionization caused by the electromagnetic field generated during the sterile-to-active neutrino conversion, and use germanium detectors’ data to set constraints on sterile neutrino properties and compare with above indirect astrophysical searches in X-ray spectra which originate from the same effective Lagrangian with the outgoing photon becomes real and observable.

Keywords: sterile neutrino, dark matter, germanium detector, direct dark matter detection