Dark Dimension Right-handed Neutrinos Confronted with Long-Baseline Oscillation Experiments

TL;DR

This work tests whether right-handed neutrinos propagating in a dark extra dimension can leave observable imprints on long-baseline oscillations. Using a 5D bulk–brane framework with KK towers, it derives both vacuum and matter oscillation probabilities and confronts predictions with T2K and NOvA data via a likelihood analysis informed by NuFIT priors. The main result is that current data are compatible with standard 3-flavor oscillations, and the DD parameter space is stringently constrained, yielding lower bounds on the bulk masses (e.g., with R = 10 μm, |c_1| ≳ 0.10 eV for NH and |c_3| ≳ 0.08 eV for IH). These findings complement collider and cosmological bounds and demonstrate that future long-baseline experiments could further probe dark-dimension scenarios, including potential CP-violating effects from KK modes.

Abstract

Right-handed neutrinos are naturally induced by dark extra dimension models and play an essential role in neutrino oscillations. The model parameters can be examined by the long-baseline neutrino oscillation experiments. In this work, we compute the predicted neutrino oscillation spectra within/without extra dimension models and compare them with the experimental data. We find that the neutrino data in the T2K and NOvA experiments are compatible with the standard neutrino oscillation hypothesis. The results set the stringent exclusion limit on the extra dimension model parameters at a high confidence level. The derived constraints on dark dimension right-handed neutrinos are complementary to those results from the collider experiments and cosmological observations.

Figures (8)

• Figure 1: Panel $(a)$ plots the values of the squared mixing coefficients in vacuum $|\mathcal{L}^i_{0(n)}|^2$ for $n = 1, \dots ,40$. Panels $(b)$, $(c)$, $(d)$ plots the values of the squared mixing coefficients $|\mathsf{L}_{10(kn)}|^2$, $|\mathsf{L}_{20(kn)}|^2$, $|\mathsf{L}_{30(kn)}|^2$, respectively. Parameters for the plots are $\bar{c}_1=-\bar{c}_2 = -\bar{c}_3 = 4$ and $\bar{\mu}_1 = 0.1$ with $\bar{\mu}_2,\bar{\mu}_3$ determined by \ref{['mu23']} in NH.
• Figure 2: Left panel: Difference on $P_{\nu_\mu\to\nu_\mu}$ with different KK modes cutoff values when {$R$, $|\bar{c}_i|$, $\bar{\mu}_1$} are set as {10 $\mu$m, 4, 0.1} and the baseline of NOvA is used. The low-pass filter is used to smooth the curves, which is discussed in Section \ref{['prob']}. Right panel: the $L^2$ norm between $P_{\nu_\mu\to\nu_\mu}$ with cutoff $\in[5,120]$ and $P_{\nu_\mu\to\nu_\mu}$ with a fixed cutoff of 200.
• Figure 3: Neutrino oscillation probabilities for both standard oscillation and DD models at the FD with a baseline of 295 km in T2K. The top (bottom) row refers to the case of neutrinos (anti-neutrinos) while the two columns show the cases of the two channels $\nu_\mu\to\nu_e$ and $\nu_\mu\to\nu_\mu$. The mass hierarchy is considered as NH. The black curves correspond to the standard oscillation case, while the other curves show the presence of the Dark Dimension with different DD parameter settings, as shown in the figure legends.
• Figure 4: Oscillation probabilities for both standard oscillation and DD models at the NOvA FD baseline of 810 km. The top (bottom) row refers to the case of neutrinos (anti-neutrinos) while the two columns show the cases of the two channels $\nu_\mu\to\nu_e$ and $\nu_\mu\to\nu_\mu$. The black curves correspond to the 4D standard oscillation scenario, while the other curves manifest deviations from it due to extra direction with different model parameter sets. The mass hierarchy is chosen to be NH.
• Figure 5: The reconstructed neutrino energy spectra for the FD $\nu_\mu$ CC and $\nu_e$ CC samples for T2K. The five subfigures refer to five channels of T2K: $\nu$-mode 1R$\mu$, $\nu$-mode 1R$e$, $\nu$-mode 1R$e$1d$e$, $\bar{\nu}$-mode 1R$\mu$ and $\bar{\nu}$-mode 1R$e$, whose order is the same as the order in datasetT2K:2023smv. The solid curves correspond to the standard oscillation, while the dashed curves correspond to the DD case with different sets of parameters, which are shown in the figure legends.