21 cm Constraints on the Lifetime of the Sterile Neutrino and Mixing Angle with Active Neutrinos

Sterile neutrinos are promising candidates for dark matter, particularly in addressing small-scale challenges of the \({ Λ }\)CDM model. These particles are radiatively unstable, decaying into active neutrinos and photons, thereby injecting energy into the intergalactic medium (IGM) during the cosmic dawn. The energy injection can alter the temperature and ionization history of IGM, impacting the global 21 cm absorption signal predicted by standard cosmological models. Using the observed 21 cm signal from the EDGES Collaboration, we derive constraints on the sterile neutrino lifetime and their mixing angle with active neutrinos. Our bounds, obtained without assuming non-standard cooling mechanisms or additional radio backgrounds, are compared with the existing astrophysical limits, such as those from X-ray observations. For sterile neutrino masses between 2 keV and 50 keV, the lifetime is constrained to be greater than \(8.3 × 10²⁷\) s to \(9.4 × 10²⁵\) s for a 21 cm brightness temperature of \( -150 \) mK at \( z=17.2\). These results provide model-independent probes of sterile neutrino parameters relevant to dark-matter phenomenology. Abstract Published by the Jagiellonian University 2026 authors