Exploring Wrong Sign Scenarios in the Yukawa-Aligned 2HDM

TL;DR

This paper investigates wrong-sign Yukawa couplings in the Yukawa-aligned 2HDM, analyzing their phenomenology, current experimental constraints, and potential signatures at the high-luminosity LHC, especially in the Type-X scenario.

Contribution

It provides a detailed analysis of the parameter space for wrong-sign Yukawa couplings, including experimental constraints and distinctive multi-Higgs signatures at the LHC.

Findings

Most of the parameter space is already explored in the WS Type-X scenario.

Multi-Higgs pair production can serve as a key signature for WS scenarios.

The phenomenology differs significantly from the right-sign case due to larger Higgs mixing.

Abstract

We discuss scenarios with wrong-sign (WS) Yukawa couplings for the discovered Higgs boson in the Yukawa-aligned two Higgs doublet model. In the WS scenario, Yukawa couplings for down-type quarks and/or charged leptons have an opposite sign as compared to those of the Higgs boson in the standard model, which can be consistent with current flavour data and the Higgs signal strengths. The phenomenology of additional Higgs bosons in such a scenario can be significantly different from that with right-sign Yukawa couplings, mainly due to a larger Higgs boson mixing to be required in the wrong-sign case. We show the parameter space which is excluded or explored by direct searches for the additional Higgs bosons at the current and high-luminosity LHC under the constraints from perturbative unitarity and vacuum stability. In particular, we find that most of the parameter space is explored in the WS scenario with the Type-X (lepton specific) Yukawa interaction which is a special case of the Yukawa alignment realized by imposing a softly-broken $\mathbb{Z}_2$ symmetry. We propose that multi-Higgs events from pair productions of the additional Higgs bosons can be the smoking gun signature to probe the WS scenario, and give the expected number of events at the high-luminosity LHC.