Kavli Affiliate: Shigeki Matsumoto
| First 5 Authors: Tatsuya Hayashi, Shigeki Matsumoto, Yuki Watanabe, Tsutomu T. Yanagida,
| Summary:
The new gauge boson introduced in the minimal extension of the standard model
(SM) by gauging the U(1)$_{rm B-L}$ symmetry plays the role of dark matter
when the U(1)$_{rm B-L}$ gauge coupling is highly suppressed. This dark
matter, named the F’eeton dark matter is known to be efficiently created in
the early universe by inflationary fluctuations with minimal gravity coupling,
hence the framework, the gauged U(1)$_{rm B-L}$ extended SM + inflation,
solves the four major problems of the SM; neutrino masses/mixings, dark matter,
baryon asymmetry of the universe, and the initial condition of the universe
(inflation). We comprehensively study the phenomenology of the dark matter when
it is heavier than the $e^- e^+$ threshold, namely twice the electron mass,
considering the threshold effect on the dark matter decay into $e^- e^+$. The
viable parameter region is found only in the threshold region, while the
branching fraction of the decay into $e^- e^+$ (i.e., the $e^- e^+$ signal)
never vanishes even at the threshold due to the effect. As a result, the pure
U(1)$_{rm B-L}$ extension without the kinetic mixing between the U(1)$_{rm
B-L}$ and hyper-charge gauge bosons have already been excluded by the present
observation of the 511,keV photon from the galactic center. So, the F’eeton
dark matter requires a non-zero kinetic mixing to be a viable dark matter
candidate and will be efficiently explored by future MeV-gamma ray telescopes
thanks to the non-vanishing decay process into $e^- e^+$.
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