Type-II 2HDM under the Precision Measurements at the $Z$-pole and a Higgs Factory

TL;DR

Future precision measurements at proposed $Z$-factories and Higgs factories can significantly constrain the parameter space of the Type-II 2HDM, especially regarding heavy Higgs masses and mass splittings, complementing direct collider searches.

Contribution

This study provides a comprehensive analysis of how future electroweak precision measurements can probe the parameter space of the Type-II 2HDM, including non-alignment and non-degenerate masses, through a global fit.

Findings

Future measurements tightly constrain $ aneta$ and Higgs mass splittings.

Indirect limits on heavy Higgs masses are derived, complementing direct searches.

Expected accuracies at $Z$-pole and Higgs factory are highly complementary.

Abstract

Future precision measurements of the Standard Model (SM) parameters at the proposed $Z$-factories and Higgs factories may have significant impacts on new physics beyond the Standard Model in the electroweak sector. We illustrate this by focusing on the Type-II two Higgs doublet model (Type-II 2HDM). The contributions from the heavy Higgs bosons at the tree-level and at the one-loop level are included in a full model parameter space. We perform a multiple variable global fit and study the extent to which the parameters of non-alignment and non-degenerate masses can be probed by the precision measurements. We find that the allowed parameter ranges are tightly constrained by the future Higgs precision measurements, especially for small and large values of $\tan\beta$. Indirect limits on the masses of heavy Higgs can be obtained, which can be complementary to the direct searches of the heavy Higgs bosons at hadron colliders. We also find that the expected accuracies at the $Z$-pole and at a Higgs factory are quite complementary in constraining mass splittings of heavy Higgs bosons. The typical results are $|\cos(\beta-\alpha)| < 0.008, |\Delta m_\Phi | < 200\ {\rm GeV}$, and $\tan\beta \sim 0.2 - 5$. The reaches from CEPC, FCC-ee and ILC are also compared, for both Higgs and $Z$-pole precision measurements.