The limits on CP-odd four-fermion operators containing strange quark field

TL;DR

This paper derives stringent limits on CP-odd four-fermion operators involving strange quarks using neutron EDM and nucleon interactions, completing the analysis of light-quark CP-odd operators and evaluating axionic vacuum shifts.

Contribution

It provides the first comprehensive bounds on strange-quark CP-odd four-fermion operators, extending previous studies on up and down flavors and analyzing their impact on the axionic vacuum.

Findings

Limits on strange-quark operators are comparable to those for up and down flavors.

Four-fermion operators induce subleading shifts in the axionic vacuum.

Constraints are derived from neutron EDM and T-odd nucleon interactions.

Abstract

The bounds on the neutron electric dipole moment and T-odd nucleon-nucleon interaction are used to extract the limits on the effective CP-odd four-fermion operators containing strange quark field. This completes the study of the dim=5,6 CP-odd operators built from the light-quark fields. The limits are very strong and comparable to those obtained previously for operators containing up and down flavors. We also analyze the shift of the axionic vacuum, $\theta_{eff}$, induced by four-fermion operators in the presence of PQ mechanism and conclude that this gives subleading contributions to CP-odd observables as compared with the direct ones.