D vs d: CP Violation in Beta Decay and Electric Dipole Moments

TL;DR

This paper analyzes the potential size of the CP-violating correlation D in beta decay, showing that neutron EDM constraints strongly limit D, especially in leptoquark models, with implications for future experiments.

Contribution

It provides a detailed analysis of how neutron and other EDM constraints limit the possible values of D in various beyond Standard Model theories.

Findings

Neutron EDM currently provides the strongest constraint on D.

Constraints on D are 10 to 1000 times stronger than direct limits.

Leptoquark models are more constrained than previously thought.

Abstract

The T-odd correlation coefficient D in nuclear beta decay probes CP violation in many theories beyond the Standard Model. We provide an analysis for how large D can be in light of constraints from electric dipole moment (EDM) searches. We argue that the neutron EDM d_n currently provides the strongest constraint on D, which is 10 - 10^3 times stronger than current direct limits on D (depending on the model). In particular, contributions to D in leptoquark models (previously regarded as "EDM safe") are more constrained than previously thought. Bounds on D can be weakened only by fine-tuned cancellations or if theoretical uncertainties are larger than estimated in d_n. We also study implications for D from mercury and deuteron EDMs.