Accommodating Hints of New Heavy Scalars in the Framework of the Flavor-Aligned Two-Higgs-Doublet Model

TL;DR

This paper investigates how hints of new heavy scalars at the LHC can be explained within the flavor-aligned two-Higgs-doublet model, analyzing experimental excesses and their compatibility with flavor symmetries.

Contribution

It proposes a method to determine if flavor alignment in the 2HDM is due to an exact or softly broken symmetry, illustrated with two scenarios based on LHC excesses.

Findings

Scenario 1 aligns with Type-I Yukawa interactions and a softly-broken Z2 symmetry.

Scenario 2 is incompatible with symmetry-based flavor alignment but fits general flavor-aligned Yukawa couplings.

Analysis suggests different flavor structures can explain observed heavy scalar excesses.

Abstract

Searches for new neutral Higgs bosons of an extended Higgs sector at the LHC can be interpreted in the framework of the two-Higgs doublet model. By employing generic flavor-aligned Higgs-fermion Yukawa couplings, we propose an analysis that uses experimental data to determine whether flavor alignment is a consequence of a symmetry that is either exact or at most softly broken. We illustrate our proposal in two different scenarios based on a few 3 sigma (local) excesses observed by the ATLAS and CMS Collaborations in their searches for heavy scalars. In Scenario 1, an excess of events is interpreted as $A\to ZH\to \ell^+\ell^- b\bar{b}$ (where $\ell=e$ or $\mu$), with the CP-odd and CP-even neutral scalar masses given by $m_A=610$ GeV and $m_H=290$ GeV, respectively. In Scenario 2, an excess of events in the production of $t\bar{t}$ and $\tau^+\tau^-$ final states is interpreted as decays of a CP-odd scalar of mass $m_A=400$ GeV. Scenario 1 is consistent with Type-I Yukawa interactions, which can arise in a 2HDM subject to a softly-broken $\mathbb{Z}_2$ discrete symmetry. Scenario 2 is inconsistent with a symmetry-based flavor alignment, but can be consistent with more general flavor-aligned Higgs-fermion Yukawa couplings.