CP-violating Higgs Di-tau Decays: Baryogenesis and Higgs Factories

TL;DR

Future lepton colliders can effectively probe CP violation in Higgs di-tau decays, offering a promising avenue to test baryogenesis mechanisms and discover new physics beyond the Standard Model.

Contribution

This paper demonstrates the potential of future lepton colliders to measure CP violation in Higgs decays with high precision, linking collider experiments to baryogenesis.

Findings

Circular Electron Positron Collider can exclude certain CP phases at 68% and 95% confidence levels.

Future colliders can achieve 5σ discovery for a significant portion of CP phase space.

Higgs factories can measure new physics effects with order-one precision.

Abstract

We demonstrate how probes of CP-violating observables in Higgs di-tau decays at prospective future lepton colliders could provide a test of weak scale baryogenesis with significant discovery potential. Measurements at the Circular Electron Positron Collider, for example, could exclude a CP phase larger than $2.9^\circ$ ($5.6^\circ$) at 68% (95%) C.L. assuming the Standard Model value for magnitude of the tau lepton Yukawa coupling. Conversely, this sensitivity would allow for a $5\,\sigma$ discovery for 82% of the CP phase range $[0,2\pi)$. The reaches of the Future Circular Collider - ee and International Linear Collider are comparable. As a consequence, future lepton colliders could establish the presence of CP violation required by lepton flavored electroweak baryogenesis with at least $3\,\sigma$ sensitivity. Our results illustrate that Higgs factories are not just precision machines but can also make $\mathcal O(1)$ measurement of the new physics beyond the Standard Model.