Kavli Affiliate: Shigeki Matsumoto
| Summary:
We explore the indirect detection of sterile neutrino dark matter within the gauged $U(1)_B-L$ extension of the Standard Model, in which three right-handed neutrinos account for neutrino masses, the baryon asymmetry, and dark matter. Focusing on the MeV mass range, we investigate two decay channels: the radiative decay $N to νγ$, which produces a monochromatic photon, and the three-body decay $N to e^- e^+ ν$, which leads to a 511 keV photon signal from positronium decay. Taking the upcoming COSI mission as a case study, we show that both signals are experimentally accessible and complementary, with the 511 keV channel extending the sensitivity reach up to $O(100)$ MeV. We propose a novel analysis strategy in Compton data space to isolate the diffuse 511 keV emission. Furthermore, we incorporate, for the first time, the Sommerfeld enhancement in the decay width of $N to e^- e^+ ν$, enabling more accurate predictions of the signal near the kinematic threshold. The combined observation of both channels would provide a distinctive and testable signature of the sterile neutrino dark matter hypothesis.
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