CP Violation in Top Physics

TL;DR

The paper addresses the absence of Standard Model CP violation in top quark processes and argues that observing CP-violating effects in top quark interactions would signal new physics with potential relevance to baryogenesis. It surveys non-standard sources from extended Higgs sectors and supersymmetry, detailing a broad set of CP-odd observables in top production and decay across e+e−, γγ, μ+μ−, pp, and p pbar colliders, including top dipole moments and CP-violating form factors. It highlights tree-level CP-violating mechanisms in processes such as e+e− → ttH, ttZ, ttνν, and in t → bW with charged-Higgs interference, as well as loop-induced effects, suggesting observable asymmetries at the percent level in favorable models and outlining collider-specific sensitivities. The review provides estimated sensitivities for top EDMs, ZEDMs, and CEDMs (around 10^−19 e-cm and 10^−19 g_s cm), discusses optimal observables and spin-based probes across collider types, and argues that top-spin measurements at future colliders offer robust avenues to detect beyond-SM CP violation, with implications for our understanding of baryogenesis.

Abstract

CP violation in top physics is reviewed. The Standard Model has negligible effects, consequently CP violation searches involving the top quark may constitute the best way to look for physics beyond the Standard Model. Non-standard sources of CP violation due to an extended Higgs sector with and without natural flavor conservation and supersymmetric theories are discussed. Experimental feasibility of detecting CP violation effects in top quark production and decays in high energy e+ e-, gamma-gamma, mu+ mu-, pp and p-bar p colliders are surveyed. Searches for the electric, electro-weak and the chromo-electric dipole moments of the top quark in e+ e- -> t-bar t and in p p -> t-bar t X are descibed. In addition, other mechanisms that appear promising for experiments, e.g., tree-level CP violation in e+ e- -> t-bar t h, t-bar t Z, t-bar t nu_e-bar nu_e and in the top decay t -> b tau nu_tau and CP violation driven by s-channel Higgs exchanges in p p, gamma gamma, mu+ mu- -> t-bar t etc., are also discussed.