Quasi-Sterile Neutrinos from Dark Sectors I. BSM matter effects in neutrino oscillations and the short-baseline anomalies

Abstract

Quasi-sterile neutrinos are a natural consequence of dark sectors interacting with the Standard Model (SM) sector via neutrino-and vector-portals. Essentially, quasisterile 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 ν e disappearance searches are also briefly discussed.

White Paper on Light Sterile Neutrino Searches and Related Phenomenology

“…More recently, [148] reiterated that these tensions with long-baseline experiments occur because new matter effects generically distort the active (anti-)neutrino mixing and mass spectrum. A dark sector model with both neutrino and vector portals was then proposed in [148] that avoids these large (2) , are shown as a function of the distance traveled by neutrinos in the Earth assuming a common m 2 J = 0.1 eV 2 . The top, middle and bottom panels are for α = e, τ , and µ, respectively.…”

Requirements on common solutions to the LSND and MiniBooNE excesses: a post-MicroBooNE study

“…Recent reviews and references on active-sterile oscillation solutions to the anomalies may be found in [8,[34][35][36][37][38]. Variants on the simple vacuum oscillation solution, which use matter effects and resonant oscillations with new mediators to produce a single electron or positron in the detector may be found in [39] (vector mediator) and [40] (scalar mediator).…”

“…Both subsets of proposals in category a) remain in contention due to reasons described in recent work [39,[46][47][48], i.e. that MicroBooNE results disfavour but do not eliminate the possibility that LSND and MB results can be explained by i) O(eV) sterile neutrinos with active-sterile mixing and oscillations, or more generally, by ii) the presence of additional ν e in the beam.…”

“…5 They also assign weightage to the systematic uncertainties present in the backgrounds at MB. Importantly, they rely on the fact that MicroBooNE mapped the MB excess to an eLEE model which is not unique, in that other ν e spectral choices can also reproduce the MB excess [39,47]. These considerations render MicroBooNE's coverage of MB's parameter space less certain and extensive, and consequently do not rule out these proposals.…”