Using dipole processes to constrain the flavour of four-fermion effective interactions

TL;DR

This paper investigates how four-fermion interactions can influence dipole moments and related phenomena, providing insights into potential new physics beyond the Standard Model through two-loop mixing effects.

Contribution

It introduces a study of four-fermion contact interactions with two-loop mixing into dipoles, highlighting scenarios avoiding small Yukawa couplings and exploring phenomenological implications.

Findings

Two-loop mixing can generate observable dipole effects.

Phenomenological consequences for flavour and CP violation are identified.

Potential constraints on new physics from dipole-related phenomena.

Abstract

Dipole interactions encode a rich variety of phenomena, such as radiative decays and electric dipole moments in both quark and lepton sectors, which probe physics beyond the Standard Model up to very high energy scales; due to renormalization, non-dipole operators mix into dipole ones, thus possibly generating observable effects that can be investigated by those same phenomena. I consider four-fermion contact interactions for which the leading order mixing into dipoles happens at two-loops (i.e., when one-loop effects vanish) and for which this mixing can avoid small Yukawa couplings, and then explore the phenomenological consequences for flavour and $ \mathbf{CP} $ violation coming from New Physics.