Investigation of the Lorentz invariance violation in two-neutrino double-beta decay

TL;DR

This paper investigates potential Lorentz invariance violation effects in two-neutrino double-beta decay, providing formulas, spectra, and methods to constrain LIV coefficients, thereby aiding experimental searches for fundamental symmetry violations.

Contribution

It offers a comprehensive theoretical framework and new analytical tools for detecting LIV effects in double-beta decay experiments, including spectra and angular correlation analyses.

Findings

LIV causes a shift of electron spectra to higher energies.

Comparison of spectra can reveal LIV signatures.

Estimated experimental statistics needed to constrain LIV coefficients.

Abstract

We make a comprehensive investigation of the Lorentz invariance violation (LIV) effects that may occur in two-neutrino double-beta ($2\nu\beta\beta$) decay for all the experimentally interesting nuclei. We deduce the formulas for the LIV deviations and provide single and summed energy electron spectra and angular correlation between electrons with and without LIV contributions, to be used for constraining the LIV coefficient $\mathring{a}_{\text{of}}^{(3)}$. First, we confirm the shifting of the electron spectra to higher electron energies due to LIV for all nuclei. Next, we analyze other LIV signatures that can be used in LIV investigations. Thus, from the comparison of the electron and angular correlation spectra calculated with the inclusion of the LIV contributions, with their standard forms, information can be obtained about the strength versus observability of the LIV effects in the current experimental statistics. Then, we present the alternative method of constraining $\mathring{a}_{\text{of}}^{(3)}$ from the measurement of the angular correlation coefficient and estimate the statistics that different double-beta decay experiments should reach to constrain the LIV coefficient at the level of the current beta decay experiments. We hope that our work will improve the theoretical support and further stimulate the search for LIV in double-beta decay.