An $\epsilon'$ improvement from right-handed currents

TL;DR

This paper explores how right-handed charged currents could explain the tension between lattice QCD calculations and experimental results on CP violation in kaon decays, suggesting a new physics scale around 100 TeV.

Contribution

It provides a detailed calculation linking right-handed currents to CP violation and electric dipole moments, proposing a testable new physics scenario at high energy scales.

Findings

Right-handed currents can account for the CP violation discrepancy.

Predicted couplings are consistent with existing precision constraints.

Next-generation EDM experiments can test this explanation.

Abstract

Recent lattice QCD calculations of direct CP violation in $K_L \to \pi \pi$ decays indicate tension with the experimental results. Assuming this tension to be real, we investigate a possible beyond-the-Standard Model explanation via right-handed charged currents. By using chiral perturbation theory in combination with lattice QCD results, we accurately calculate the modification of $\epsilon'/\epsilon$ induced by right-handed charged currents and extract values of the couplings that are necessary to explain the discrepancy, pointing to a scale around $10^2$ TeV. We find that couplings of this size are not in conflict with constraints from other precision experiments, but next-generation hadronic electric dipole moment searches (such as neutron and ${}^{225}$Ra) can falsify this scenario. We work out in detail a direct link, based on chiral perturbation theory, between CP violation in the kaon sector and electric dipole moments induced by right-handed currents which can be used in future analyses of left-right symmetric models.