Probing Geometrical NSI at the DUNE experiment

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.

💡 Research Summary

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In this paper the authors investigate a novel class of non‑standard neutrino interactions (NSI) that arise from spacetime torsion in a curved background. In Einstein‑Cartan‑type theories the torsion field does not propagate; it can be eliminated from the action, leaving behind a four‑fermion contact term. For neutrinos this term takes the form
( H_{\rm I}= \sum_{i=1}^{3}\lambda_i,\nu_i^{\dagger L}\nu_i^{L},\tilde n),
where (\lambda_i) are length‑dimension couplings and (\tilde n) is a weighted number density of background fermions (electrons, up‑ and down‑quarks). Because the interaction is diagonal in the mass basis, only the differences (\lambda_{21}=\lambda_2-\lambda_1) and (\lambda_{31}=\lambda_3-\lambda_1) affect oscillations.

The effective Hamiltonian in the flavor basis is written as
\