Ultra-light scalar saving the 3 + 1 neutrino scheme from the cosmological bounds

Abstract

The LSND and MiniBooNE results as well as the reactor and Gallium anomalies seem to indicate the presence of a sterile neutrino with a mass of ∼ 1 eV mixed with active neutrinos. Such sterile neutrino can be produced in the early universe before the neutrino decoupling, leading to a contribution to the effective number of neutrinos (N ef f ) as well as to a contribution to the sum of neutrino masses which are in tension with cosmological observations. We propose a scenario to relax this tension by a Yukawa coupling of the sterile neutrinos to ultra-light scalar particles which contribute to the dark matter in the background. The coupling induces an effective mass for νs which prevents its production in the early universe. We discuss the implications for the upcoming KATRIN experiment and future relic neutrino search experiments such as PTOLEMY. We also briefly comment on certain non-renormalizable forms of interaction between νs and the scalar and their consequences for the νs production in the early universe. * yasaman@theory.ipm.ac.ir

Decaying sterile neutrinos and the short baseline oscillation anomalies

“…However, the constraint could be substantially weakened in extensions of our model, see for instance Refs. [67][68][69][70]. A minimalist example is the production of extra species of light particles at the expense of the neutrino sector after neutrino decoupling.…”

Signatures of ultralight dark matter in neutrino oscillation experiments

“…Although we use Fuzzy DM and neutrino masses as a motivation, we are indeed more concerned with general experimental signatures, and thus we adopt a bottom-up approach in this work. Some of these signatures were explored in previous literature [28][29][30][31][32][33][34][35][36][37][38][39]. Here we will provide a more detailed analysis, with special emphasis on aspects directly connected to experimental searches, and highlighting the different regimes relevant to neutrino oscillation phenomenology.…”

On the τ flavor of the cosmic neutrino flux

“…Moreover, the 3 + 1 scheme is ruled out by the cosmological bounds on the extra relativistic degrees of freedom in the early universe. As shown in [16], the coupling of neutrinos to ultralight dark matter can save the 3 + 1 scheme from the cosmological bounds as the effective induced flavor diagonal mass in the early universe will be large enough to suppress the effective mixing and therefore the ν s production in the early universe. We revisit the 3 + 1 solution to the ANITA events in the presence of DM effects and show that the solution can be revived because the accompanying ν τ flux that reach the Earth can be small.…”