Kavli Affiliate: Shigeki Matsumoto
| First 5 Authors: Subaru Fujisawa, Subaru Fujisawa, , ,
| 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 $N to nu gamma$, which produces a monochromatic photon,
and the three-body decay $N to e^- e^+ nu$, 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 $N to e^- e^+
nu$, 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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