Neutrino astronomy as a probe of physics beyond the Standard Model:
  decay of sub-MeV $B$-$L$ gauge boson dark matter
  The $U(1)_{B\textrm{--}L}$ symmetry, the essential component in the seesaw
mechanism and leptogenesis, is naturally equipped with a massive gauge boson.
When the gauge coupling is of the order of $\mathcal{O}(10^{-19})$, this gauge
boson is a light and long-lived dark matter candidate which dominantly decays
into active neutrinos. This consistent dark matter scenario predicts a
characteristic neutrino signal that is potentially detectable at future
neutrino observatories. Once detected, such a neutrino signal would serve as a
smoking gun for this minimal extension to the Standard Model of particle
physics, opening new windows to tackle cosmological and astrophysical conundra.
