Dark NSI & neutrino oscillations : probing via $δ_{CP}$ measurements at DUNE and T2HK

TL;DR

This paper analyzes dark NSI arising from a coherent background of ultralight scalar dark matter and their impact on long-baseline neutrino oscillations. The authors derive a mass-squared correction $δM^2_{αβ}$ that enters the neutrino Hamiltonian with opposite signs for neutrinos and antineutrinos, and they parametrize the effect with diagonal real and off-diagonal complex couplings $d_{αβ}$ and phases $φ_{αβ}$, scaled by $S_m^2$ and the DM density $ρ_χ$. Using DUNE and T2HK configurations and a GLoBES-based simulation, they show that off-diagonal dark NSI can substantially distort CP observables such as $P_{μe}$, the CP asymmetry $A^{μe}_{CP}$, and CP-violation sensitivity, with the impact depending on the phases $φ_{αβ}$ and the baseline energy. Crucially, the combination of DUNE and T2HK mitigates degeneracies induced by dark NSI phases and can restore or even enhance CP sensitivity relative to the standard oscillation scenario, highlighting the importance of joint analyses in probing neutrino interactions with the dark sector.

Abstract

We investigate the possibility of neutrinos interacting with a scalar dark matter field and the resulting implications for neutrino oscillations in the long-baseline sector. As our Universe is predominantly composed of dark matter, neutrinos propagating over astrophysical and terrestrial baselines inevitably traverse a dark matter background. The coherent forward scattering of neutrinos in such a background induces a medium-dependent correction to the mass-squared term in the effective neutrino Hamiltonian having opposing signs for neutrinos and antineutrinos. We study how the elements of this correction matrix, arising from coherent forward scattering of neutrinos with scalar dark matter background referred to as dark non-standard interactions (dark NSI), modify neutrino oscillation probabilities. Furthermore, we also study the effect of the off-diagonal elements and the associated phases on the measurement of leptonic CP violating phase focusing on the upcoming long-baseline superbeam experiments DUNE and T2HK. We show that dark NSI can lead to substantial enhancement or suppression of CP-violation sensitivity, depending on the true values of the dark NSI phases $φ_{αβ}$. We further explored how the synergy of DUNE and T2HK can effectively mitigate the degeneracies due to the dark NSI phases, and can restore or even enhance the CP sensitivity as compared to the standard oscillation scenario.

Figures (10)

• Figure 1: Feynman diagram for neutrino forward scattering with scalar $\phi$Ge:2019tdi.
• Figure 2: Appearance probability $P_{\mu e}$ (top) and disappearance probability $P_{\mu \mu}$ (bottom) for DUNE ( L=1300 km), NO, $\delta_{CP}= -90^\circ$ for different values of the diagonal dark NSI parameters $\eta_{ee}$ (left), $\eta_{\mu \mu}$ (middle), and $\eta_{\tau \tau}$ (right).
• Figure 3: $P_{\mu e}$ (top), $P_{\mu \mu}$ (bottom) for DUNE ( L=1300 km), NO, $\delta_{CP}= -90^\circ,~\phi_{\alpha \beta}= 0^\circ$ for different values of the off-diagonal dark NSI parameters $\eta_{e\mu }$ (left), $\eta_{e \tau}$ (middle) $\eta_{\mu \tau}$ (right).
• Figure 4: Appearance probability $P_{\mu e}$ (top) and disappearance probability $P_{\mu \mu}$ (bottom) for T2HK ( L=295 km), NO, $\delta_{CP}= -90^\circ$ for different values of the diagonal dark NSI parameters $\eta_{ee}$ (left), $\eta_{\mu \mu}$ (middle), and $\eta_{\tau \tau}$ (right).
• Figure 5: $P_{\mu e}$ (top), $P_{\mu \mu}$ (bottom) for T2HK ( L=295 km), NO, $\delta_{CP}= -90^\circ,~\phi_{\alpha \beta}= 0^\circ$ for different values of the off-diagonal dark NSI parameters $\eta_{e\mu }$ (left), $\eta_{e \tau}$ (middle) $\eta_{\mu \tau}$ (right).