Mass Varying Neutrino Oscillation in Scalar-Gauss-Bonnet Gravity

TL;DR

The paper investigates mass-varying neutrino oscillations within a scalar–Gauss–Bonnet gravity framework, where a scalar field coupled to the Gauss–Bonnet invariant induces environment-dependent neutrino masses. It derives the scalar-field profile in a Sun-like, static, spherically symmetric spacetime and formulates a modified two-flavor MSW-like evolution with a quartic φ-dependence, then constrains the model using solar-neutrino data via a χ^2 analysis. The global fit yields best-fit parameters ξ' ≈ 7.83×10^{11} and Δκ'²_{21} ≈ 1.02×10^{-23} eV², with Δm²_{21} inside the Sun around 2.87×10^{-23} eV², consistent with the LMA–MSW solution. This work connects modified gravity with neutrino physics, showing solar neutrino data can constrain sGB gravity and pointing to future tests at next-generation neutrino experiments.

Abstract

We investigate how matter density affects neutrino oscillations by considering a mass-varying neutrino scenario where the neutrino mass depends on a scalar field. This scalar field is non-minimally coupled to the Gauss-Bonnet (GB) invariant, causing its profile to be implicitly influenced by the surrounding matter distribution. Using data from solar neutrino experiments, we derive constraints on the model parameters, providing new insights into the properties of mass-varying neutrino within the Gauss-Bonnet scalar-tensor framework.

Figures (6)

• Figure 1: The dimensionless scalar field profile as a function of the dimensionless fractional radius $r^\prime$. These cases correspond to $r_s^{\prime}= 4.17\times 10^{-6}$ (the solar case) and $\xi^\prime \in \{7 \times 10^{11}, 8 \times 10^{11}, 9\times 10^{11}\}$. At large distances, the scalar field exhibits smooth behavior, see panel (a). Panel (b) is drawn to illuminate the dependence of $\hat{\phi}(r^\prime)$ on the parameters inside and near the surface of the object.
• Figure 2: The analysis of confidence regions (1$\sigma$, 2$\sigma$, and 3$\sigma$) for the model parameters $\xi^\prime$ (dimensionless) and $\Delta \kappa^{\prime 2}_{21}$ (in eV$^2$). The best-fit values are shown by asterisks.
• Figure 3: Survival probability $P_{ee}(E_\nu)$ of solar neutrinos in terms of neutrino energy for LMA-MSW solution, and different curves of LMA-MSW + scalar-neutrino non-standard couplings for six various situations. In this figure, the gray band shows the curve from standard matter effects (i.e., the case without scalar field) within $\pm 1\sigma$ C.L., and the horizontal dotted lines show the cases with large/small model parameters $\xi^\prime$ or $\Delta \kappa_{21}^{\prime 2}$.
• Figure 4: Figure shows the ratio of mass function of neutrinos in terms of dimensionless radius $r^\prime$, derived from the optimal fits of solar neutrino experiments. This figure, in fact, shows the sensitivity of neutrino mass to non-minimal coupling parameter $\xi^\prime$. The inset plot illustrates the behavior of the mass function inside the Sun.
• Figure 5: Variation of the squared mass difference $\Delta m_{21}^2(r^\prime)$ as a function of dimensionless fractional radius ($r^\prime$). This would be a comparative analysis from Borexino, SNO, Kamiokande, SK, and Global fits. Determined value on each curve indicates the asymptotic mass-squared splitting.