Solar Neutrino Flux Fluctuations Caused by Solar Gravity Modes

TL;DR

This paper analyzes how solar gravity modes could cause fluctuations in neutrino flux, concluding that detecting individual g-modes via neutrino measurements is currently unfeasible, but long-term flux variations may reveal their presence.

Contribution

It provides a theoretical evaluation of solar g-mode effects on neutrino flux, highlighting the potential for indirect detection through long-term flux variations.

Findings

First-order flux fluctuation is zero due to geometrical cancellation.

Second-order fluctuation is non-zero but too small for current detection.

Long-term neutrino flux variations could indicate solar g-modes and solar activity cycle influence.

Abstract

We have evaluated fluctuations in neutrino fluxes caused by solar gravity (g) modes based on the analysis of linear adiabatic oscillation of a spherically symmetric star. We find that the first-order fluctuation is zero due to geometrical cancellation. We still find that the second-order fluctuation is non-zero, which consists of time-varying and non-time-varying components. The amplitude of the time-varying component is small (${\sim} 10^{-9}$ in relative difference, in the case of $\mathrm{^{8}B}$ neutrino) and well below the detection limits of the current neutrino detectors, when we assume the g-mode amplitude parameter $A_{n \ell}$ to be $10^{-5}$, which corresponds to the assumed maximum relative temperature perturbation inside the Sun. Thus, it is at the moment fair to say that detecting individual solar g-modes via the solar neutrino flux measurement is almost impossible. However, the net increase in the mean neutrino flux that originates from the non-time-varying component could be non-negligible. In particular, since $A_{n \ell}$ may be related to convection amplitude, which could change in accordance with the solar magnetic activity, the total net increase in the neutrino flux, which is proportional to $A_{n \ell}^2$, should also change with the solar activity cycle. Such a long-period variation~(${\sim} 11$~years) in the neutrino flux could thus be interpreted as evidence for a bunch of solar g-modes. Comparison of the theoretical prediction with the solar neutrino measurements by, e.g., Super-Kamiokande, may have a potential to put constraints on the theory of the excitation mechanism of solar g-modes.