Neutrinos in large extra dimensions and short-baseline ${\nu }_e$ appearance

We show that, in the presence of bulk masses, sterile neutrinos propagating in large extra dimensions (LED) can induce electron-neutrino appearance effects. This is in contrast to what happens in the standard LED scenario, and hence LED models with explicit bulk masses have the potential to address the MiniBooNE and LSND appearance results as well as the reactor and Gallium anomalies. A special feature in our scenario is that the mixing of the first Kaluza-Klein modes to active neutrinos can be suppressed, making the contribution of heavier sterile neutrinos to oscillations relatively more important. We study the implications of this neutrino mass generation mechanism for current and future neutrino oscillation experiments and show that the Short Baseline Neutrino Program at Fermilab will be able to efficiently probe such a scenario. In addition, this framework leads to massive Dirac neutrinos and thus precludes any signal in neutrinoless double beta decay experiments.

Figure 1

The mass of the zero mode (red lines) and of the first KK mode (dashed blue lines) as a function of the radius $R$ and the bulk mass $c$ times $R$. We fix the scale $M_5={10}^6\mathrm{GeV}$, ${\lambda }_i=0.66$.

Figure 2

Pattern of KK masses and mixings for the benchmark point 1 in Table 1 with $i=1$ (turquoise) and $i=2$ (red). For comparison, we also present the equivalent pattern for LED without bulk mass terms (crosses).

Figure 3

Masses and mixings with active neutrinos of the first three KK modes as a function of the bulk mass parameter times the radius of the extra dimension, $c_{i}R$. The other $\mathrm{LED}+$ parameters are taken to be $R=1.9{\mathrm{eV}}^{-1}$, ${\lambda }_i=2.0$, and $M_5={10}^6\mathrm{GeV}$.

Figure 4

Oscillation probabilities for the three benchmark points given in Table 1 for short and long baselines as indicated in the plots. In the lower panel, the ratio of far-to-near detector probabilities is presented.

Figure 5

Near-to-far ratio of events for the ${\nu }_{\mu }\to {\nu }_{\mu }$ disappearance channel at MINOS and $\mathrm{MINOS}+$, normalized to 1 in the absence of oscillations. The red line is the expected ratio for the standard 3-neutrino framework. The light-red band shows a 5% systematic uncertainty, while the blue band corresponds to the statistical uncertainty assuming a full run [38]. Black, green, and magenta are the ratios for points 1, 2, and 3, respectively.

Figure 6

Near-to-far ratio of events for the ${\nu }_{\mu }\to {\nu }_{\mu }$ disappearance channel at $\mathrm{NO}\nu \mathrm{A}$, normalized to 1 in the absence of oscillations. The red line is the expected ratio for the standard 3-neutrino framework. The light-red band shows a 5% systematic uncertainty, while the blue band corresponds to the statistical uncertainty assuming $3\times {10}^{21}$ protons on target. Black, green, and magenta are the ratios for points 1, 2, and 3 in Table 1, respectively.

Figure 7

Ratio between $\mathrm{LED}+$ and standard oscillations for ${\overline{\nu }}_e\to {\overline{\nu }}_e$ disappearance events at a reactor neutrino experiment for an illustrative baseline of 10 m. The orange dashed line is the ratio between the total number of observed to expected events. The light-red band shows a 5% theoretical uncertainty. The red, black, green, and magenta lines display the ratios for the standard scenario and benchmark points 1, 2, and 3 in Table 1, respectively.

Figure 8

${\overline{\nu }}_e$ appearance spectrum at LSND (top) and ${\nu }_e$ appearance MiniBooNE for the neutrino (middle) and antineutrino (bottom) modes. The shaded histograms are the different background components as indicated in the legend (taken from Ref. [7] for LSND and Ref. [8] for MiniBooNE). Black, green, and magenta lines are for points 1, 2, and 3 in Table 1, respectively.

Figure 9

Near-to-far ratio for the ${\nu }_{\mu }\to {\nu }_{\mu }$ disappearance channel at DUNE. The red line is the expected ratio for the standard 3-neutrino framework. The light-red (blue) band shows the 5% systematic (statistical) uncertainty assuming a run of three years. Black, green, and magenta are the ratios for points 1, 2, and 3 in Table 1, respectively.

Figure 10

${\nu }_e$ appearance spectrum at SBN detectors: (top) LAr1-ND, (middle) MicroBooNE, and (bottom) ICARUS-T600. Full data sets at these three detectors are assumed (see the text). The shaded histograms are the different background components as indicated in the legend (taken from Ref. [31]). Black, green, magenta, and orange lines are for points 1, 2, and 3 in Table 1 and the best-fit $3+1$ sterile neutrino model, respectively.

Figure 11

Present and future constraints, in the plane $R\times m_0$, by MINOS (gray solid line), reactor short-baseline experiments (gray dashed line; 5% flux uncertainty is assumed), DUNE (red dashed line), and for the Short-Baseline Neutrino Program at Fermilab (blue line; appearance mode only). For reference, the light-gray shaded region indicates large active-sterile mixing, namely, $\sum _i(1-|W_i^{00}{|}^2)=0.3$. In the dark-gray shaded region, the approximation used to obtain $\mathrm{\Delta }{m}_{21}^2$ and $\mathrm{\Delta }{m}_{31}^2$ fails.