Probing Geometrical NSI at the DUNE experiment

TL;DR

This work introduces a geometry-origin NSI for neutrinos arising from spacetime torsion within ECSK gravity, leading to a torsion-induced four-fermion interaction that modifies matter effects in neutrino oscillations. The authors derive the effective Hamiltonian and oscillation probabilities using a Cayley-Hamilton perturbative approach and quantify the impact on DUNE’s ability to determine the mass hierarchy, $ heta_{23}$ octant, and the CP phase $ ext{delta_CP}$, including the emergence of new degeneracies. Through a detailed GLoBES-based simulation with a 1300 km baseline and a 40 kt detector, they constrain the torsion parameters $ lambda_{21}$ and $ lambda_{31}$ and demonstrate that while hierarchy sensitivity remains strong, octant sensitivity can be significantly degraded in certain regions due to torsion-induced degeneracies. The study highlights the importance of combining neutrino and antineutrino data to lift degeneracies and suggests future multi-experiment analyses to further constrain geometrical NSI effects and clarify their phenomenological consequences for long-baseline neutrino experiments.

Abstract

In this work, we investigate the implications of a novel non-standard interaction (NSI) of neutrinos. This interaction is geometric in origin -- it arises because the propagation of fermions in curved spacetime induces torsion. This torsion is non-propagating and can be eliminated from the action, resulting in a four-fermion interaction in a torsion-free background. The new interaction modifies the behaviour of the neutrinos passing through matter by introducing additional coupling terms, resulting in a new component in the effective potential. As a result, the neutrino oscillation probabilities in matter are altered. The relevant probabilities are computed using the Cayley-Hamilton formalism. We then numerically explore the potential to probe these torsion-induced NSI in the DUNE experiment. We obtain the bounds on the parameters characterizing the torsional effects. By selecting representative values of torsion parameters to which the DUNE experiment is sensitive, we analyse how these geometric interactions affect the experiment's sensitivity to determine neutrino mass hierarchy, the octant of the 2-3 leptonic mixing angle, and the CP phase. We also examine the new parameter degeneracies introduced by torsion effects and assess their impact on the overall sensitivities of DUNE. We find that the additional parameter degeneracies in the presence of torsion significantly affect the octant sensitivity.

Figures (11)

• Figure 1: $P_{\mu e}$ vs $E$ for NH (left panel) and IH (right panel). The bands are generated by varying $\delta_{CP} \in [-180^\circ, 180^\circ]$ , the colours indicate the sign of $\lambda_{(2,3)1}$ , with $\lambda_{e,u,d}=0.1$ , while the other parameters are taken from Table \ref{['tab:oscillation-params']}.
• Figure 2: Same as in Fig. \ref{['CP-band:DUNE']} but for $P_{\bar{\mu}\bar{e}}$.
• Figure 3: $P_{\mu e}$ and $P_{\bar{\mu} \bar{e}}$ vs $\delta_{CP}$ at $E=2.5$ GeV. The bands are due to the variation of $\theta_{23} \in [39^\circ, 42^ \circ]$ for LO and $\theta_{23} \in [48^\circ, 51^ \circ]$ for HO.
• Figure 4: Projected $3\sigma$ bounds on $\lambda_{(2,3)1}$ from DUNE. The (left) right panel shows the bounds on the geometrical couplings with the (normal) inverted hierarchy. The top panels show the bounds without any marginalization in the test spectrum. The bottom panels show the bounds with marginalization over $\delta_{CP}, \theta_{23}, \Delta m_{31}^{2}$ in the test spectrum.
• Figure 5: Mass hierarchy sensitivity as a function of true $\delta_{CP}$, in DUNE, for true values of $\theta_{23}=41^\circ$(left column) and $49^\circ$ (right column) for both NH (top row) and IH (bottom row).The green curve represents the standard scenario. The red and blue curves are for $\lambda_{(2,3)1} = 0.06$ and $\lambda_{(2,3)1} = -0.06$ in the true spectrum respectively.