Probing Solar Neutrino Deficit via Torsion-Induced Flavor Change in f(T) Gravity

TL;DR

This work develops a theoretical framework in $f(T)$ gravity to assess how spacetime torsion can influence neutrino flavor oscillations. By deriving an effective torsion–neutrino coupling from the Dirac action and solving in both vacuum and matter, it produces analytic expressions for torsion-induced phase shifts and modified mass–squared differences, leading to MSW-like modifications in solar environments. Using solar-neutrino data from SK, SNO, Borexino, and KamLAND, the authors perform a global fit that yields mild preferences for positive values of the gravity parameter $eta$ and the neutrino–torsion coupling difference $ riangle ext{κ}$, while keeping the standard teleparallel gravity limit ($eta=0$, $ riangle ext{κ}=0$) viable at 2σ. The results demonstrate that neutrino oscillations offer a novel probe of teleparallel modifications to gravity, providing competitive constraints and guiding future observational tests with upcoming neutrino experiments.

Abstract

We investigate whether the spacetime torsion can modify neutrino flavor oscillations in f(T) gravity. This offers a probe of modified teleparallel gravity in astrophysical environments. By using the Dirac action in teleparallel geometry, we derive an effective coupling between the torsion vector and neutrino current. In the weak-field limit around a spherical mass, we obtain analytical expressions for torsion-induced phase shifts and effective mass-squared differences. Our results indicate that both vacuum oscillations and the Mikheyev-Smirnov-Wolfenstein (MSW) resonance in matter are affected by these torsion-based modifications. Using solar neutrino data from Super-Kamiokande, SNO, Borexino, and KamLAND, we constrain the teleparallel model parameters and also the neutrino-torsion coupling.

Figures (6)

• Figure 1: This figure displays the $\nu_e$ survival probability in vacuum as a function of $E_\nu/R_\odot$ for different $\Delta\kappa^{(ij)}$ values, with $\alpha$ fixed at $\mathcal{O}(1~m^2)$.
• Figure 2: Radial and energy dependence of the effective solar mass-squared splitting. The mass-squared splitting tends to a constant value at large distances, corresponding to the LMA solution (cf. Table \ref{['table1']}). This behavior reflects torsion-induced modifications to neutrino oscillations in vacuum. We have set the model parameter $\alpha \sim\mathcal{O}(1~m^2)$ and two possible values for the coupling difference $|\Delta\kappa^{(ij)}| \sim\mathcal{O}(10^{-1})$ (left panel) and $|\Delta\kappa^{(ij)}| \sim\mathcal{O}(10^{-2})$ (right panel). Solid curves represent positive $\Delta\kappa^{(ij)}$ values, and dashed curves represent negative ones.
• Figure 3: Transition between matter and vacuum-dominated neutrino oscillation regimes. This figure is plotted for various values of the model parameter $\alpha$ (in units $m^2$). We have assumed that $\Delta \kappa \simeq 10^{-3}$. The observational data are taken from Borexino Borexino (gray points) and SNO+SK SNO+SK (a single black point).
• Figure 4: This figure displays $P_{ee}$ versus neutrino energy $E_\nu$ for various selected $\Delta\kappa$ values and for $\alpha \sim \mathcal{O}(1~m^2)$.
• Figure 5: (a) Matter-to-vacuum transition in neutrino oscillations under $f(T)$ gravity. The plot displays the evolution of the survival probability $P_{ee}$ across varying strengths of the model parameter $\alpha[m^2]$, for each observational dataset. (b) $P_{ee}$ as a function of the coupling difference $\Delta\kappa [10^{-3}]$.