  Quasi-sterile neutrinos are a natural consequence of dark sectors interacting
with the Standard Model (SM) sector via neutrino- and vector-portals.
Essentially, quasi-sterile neutrinos are light dark sector fermions with two
generic properties: (i) they mix with the active neutrinos of the SM, and (ii)
they are charged under a vector mediator that couples feebly to SM matter.
Various interesting phenomenological consequences result from this class of
particles. In this article, we investigate one such consequence: new, beyond
the SM matter effects that can alter in-medium neutrino oscillations. In
particular, for special windows of energy and matter densities, active
neutrinos can resonantly oscillate into sterile neutrinos. We take advantage of
this feature to build a quasi-sterile neutrino model that can explain the
MiniBooNE and LSND anomalies, while remaining compatible with observations from
long-baseline reactor- and accelerator-based neutrino experiments. This model
is also likely compatible with the recent results reported by the MicroBooNE
collaboration (albeit we cannot precisely quantify this claim due to a lack of
information in MicroBooNE's public data releases to date). Implications for
solar neutrinos and $\nu_e$ disappearance searches are also briefly discussed.
