New light Higgs boson and short-baseline neutrino anomalies

The low-energy excesses observed by the MiniBooNE experiment have, to date, defied a convincing explanation under the standard model even with accommodation for nonzero neutrino mass. In this paper we explore a new oscillation mechanism to explain these anomalies, invoking a light neutrinophilic Higgs boson, conceived to induce a low Dirac neutrino mass in accord with experimental limits. Beam neutrinos forward scattering off of a locally overdense relic neutrino background give rise to a novel matter effect with an energy-specific resonance. An enhanced oscillation around this resonance peak produces flavor transitions which are highly consistent with the MiniBooNE neutrino- and antineutrino-mode data sets. The model provides substantially improved ${\chi }^2$ values beyond either the no-oscillation hypothesis or the more commonly explored $3+1$ sterile neutrino hypothesis. This mechanism would introduce distinctive signatures at each baseline in the upcoming short-baseline neutrino program at Fermilab, presenting opportunities for further exploration.

Figure 1

Feynman diagrams for scattering of neutrinos off CNB neutrinos and antineutrinos. Top row: diagrams 1 and 2. Bottom row: diagrams 3 and 4.

Figure 2

Example oscillation probabilities at a 500 m baseline for different values of $E_{\mathrm{res}}$, $Y$, $g$. Top: Oscillation under the zero width approximation. Bottom: Oscillation for a finite width.

Figure 3

Allowed regions of the resonance oscillation effect in the zero width approximation (ZWA) to the MiniBooNE data. Left: fits to neutrino mode only; center: antineutrino mode only; right: combined fit. Top: inverted mass ordering; bottom: normal mass ordering. Stars show the best-fit points in each ordering, and the square shows the local minimum in the high mass island.

Figure 4

Oscillation spectra in allowed regions under ZWA. Top: neutrino mode. Bottom: antineutrino mode. Left to right: low-mass best fit in inverted ordering ($E_{\mathrm{res}}=100\mathrm{MeV}$, $Y=6\times {10}^{-2}{\mathrm{eV}}^2$); high-mass allowed point in inverted ordering ($E_{\mathrm{res}}=340\mathrm{MeV}$, $Y=1.4\times {10}^{-3}{\mathrm{eV}}^2$); example allowed point in normal ordering ($E_{\mathrm{res}}=320$, $Y=3\times {10}^{-2}{\mathrm{eV}}^2$) region.

Figure 5

Slices of the allowed regions at fixed $g$ given the finite width model (3 DOF) under the normal ordering. Left: fits to neutrino mode only; center: antineutrino mode only; right: combined fit.

Figure 6

Predictions for the oscillation probability for the SBN program for the favored high and low energy resonance solutions in IO (left and center) and an example allowed point in the NO (right).

Figure 7

The 90% C.L. best-fit regions expressed in terms of coupling strength to the heaviest neutrino state and CNB overdensity, compared to various 90% C.L. experimental limits described in the text.