Nonperturbative effects in neutrino magnetic moments

TL;DR

This paper investigates nonperturbative QCD effects on neutrino magnetic moments, constrains effective field theory coefficients using experimental data, and highlights the dominance of nonperturbative contributions in certain quark channels.

Contribution

It provides the first detailed calculation of nonperturbative QCD contributions to neutrino magnetic moments and compares them with perturbative effects in low-energy effective field theory.

Findings

Nonperturbative effects dominate for up and down quark contributions in neutrino-electron scattering.

Indirect contributions in CEνNS are negligible compared to direct contributions.

Upper bounds on tensor Wilson coefficients depend on the nonperturbative parameter c_T.

Abstract

In this paper, we calculate the QCD nonperturbative contributions of the neutrino-quark tensor operators to the neutrino magnetic moments by matching onto the chiral perturbation theory at low energies. These nonperturbative contributions can be compared to the perturbative ones, which are induced from one-loop mixing when performing the renormalization group evolutions from $\mu=m_W$ down to $\mu=2~\mathrm{GeV}$. We then constrain the dipole and tensor Wilson coefficients of the low-energy neutrino effective field theory (LNEFT) separately from the neutrino-electron scattering with Borexino data and coherent elastic neutrino-nucleus scattering (CE$\nu$NS) with COHERENT data to show the competition between these two contributions, at the renormalization scales $\mu=2~\mathrm{GeV}$ and $\mu=m_W$ in the $\bar{\mathrm{MS}}$ scheme. In the neutrino-electron scattering, it is found that the nonperturbative contributions dominate for the coefficients involving up and down quarks, while they are expected to be of the same order of magnitude as the perturbative contributions for the coefficients involving strange quark. As for constraints in the CE$\nu$NS, the tensor operators can contribute to the process through either direct or indirect way. As a result, the indirect contributions including nonperturbative and perturbative parts for all couplings become negligible in comparison with the direct ones. As the nonperturbative contributions crucially depend on the value of $c_T$, its inputs will affect the extraction of limits on the tensor LNEFT Wilson coefficients. We compute the upper bounds on these coefficients with $c_T$ quoting from the model and lattice estimates.