# Precision analysis of pseudoscalar interactions in neutron beta decays

## TL;DR

This paper investigates the pseudoscalar interactions in neutron beta decays, quantifying Standard Model and beyond Standard Model contributions, and constrains the effective coupling constants to guide experimental searches at high precision.

## Contribution

It provides a detailed analysis of pseudoscalar contributions, including the one-pion-pole exchange and BSM effects, with constraints on the effective coupling constants.

## Key findings

- OPP exchange contribution is approximately -10^{-5}.
- Constraints on BSM pseudoscalar coupling: -3.5×10^{-5} < ReC^{BSM}_ps < 0.
- Imaginary part of C^{BSM}_ps is less than -2.3×10^{-5}.

## Abstract

We analyze the contributions of the one-pion-pole (OPP) exchange, caused by strong low-energy interactions, and the pseudoscalar interaction beyond the Standard Model (BSM) to the correlation coefficients of the neutron beta-decays for polarized neutrons, polarized electrons and unpolarized protons. The strength of contributions of pseudoscalar interactions is defined by the effective coupling constant C_ps = C^(OPP)_ps + C^(BSM)_ps. We show that the contribution of the OPP exchange is of order C^(OPP)_ps ~ - 10^(-5). The effective coupling constant C^(BSM)_ps of the pseudoscalar interaction BSM can be in principle complex. Using the results, obtained by Gonzalez-Alonso et al.( Prog. Part. Nucl. Phys. 104, 165 (2019)) we find that the values of the real and imaginary parts of the effective coupling constant C^(BSM)_ps are constrained by - 3.5x10^{-5} < ReC^(BSM)_ps < 0 and ImC^(BSM)_ps < - 2.3x10^(-5), respectively. The obtained results can be used as a theoretical background for experimental searches of contributions of interactions BSM in asymmetries of the neutron beta-decays with a polarized neutron, a polarized electron and an unpolarized proton at the level of accuracy of a few parts of $10^{-5}$ or even better (Abele, Hyperfine Interact.237, 155 (2016)).