  One loop correction to the dark matter (DM) annihilation cross section is
usually assumed to be sub-dominate in calculating the DM relic density. In this
paper, we propose a scenario where DM freezes out mainly via loops in the
neutrino portal. For a scalar DM annihilating into neutrino via a triangle
diagram, or a Majorana DM annihilating into neutrino via a box diagram, the
observed DM relic density can be generated if the mediator is Majorana fermion.
We further work out the neutrino Debye mass and neutrino oscillation
probabilities in the dark halo. Numerical results show that impactions of DM to
these physical observables are negligible on the Earth, however the analytical
results can be applied to evaluate neutrino properties in a dense DM
environment.
