Neutrino forces in neutrino backgrounds

TL;DR

This paper calculates how neutrino backgrounds, such as from the sun or reactors, can significantly enhance the feeble neutrino-mediated force between fermions, making it potentially detectable with current experiments.

Contribution

It provides the first detailed computation of neutrino forces in the presence of neutrino backgrounds, revealing directional enhancements and experimental prospects.

Findings

Neutrino backgrounds can enhance the neutrino force by many orders of magnitude.

The force exhibits a 1/r dependence in the presence of directional neutrino backgrounds.

Current fifth force experiments are close to detecting this enhanced neutrino force.

Abstract

The Standard Model predicts a long-range force, proportional to $G_F^2/r^5$, between fermions due to the exchange of a pair of neutrinos. This quantum force is feeble and has not been observed yet. In this paper, we compute this force in the presence of neutrino backgrounds, both for isotropic and directional background neutrinos. We find that for the case of directional background the force can have a $1/r$ dependence and it can be significantly enhanced compared to the vacuum case. In particular, background effects caused by reactor, solar, and supernova neutrinos enhance the force by many orders of magnitude. The enhancement, however, occurs only in the direction parallel to the direction of the background neutrinos. We discuss the experimental prospects of detecting the neutrino force in neutrino backgrounds and find that the effect is close to the available sensitivity of the current fifth force experiments. Yet, the angular spread of the neutrino flux and that of the test masses reduce the strength of this force. The results are encouraging and a detailed experimental study is called for to check if the effect can be probed.