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

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.

Comments: 49 pages, 19 figures, 15 tables; v2: minor tweaks and some added references; v3: better implementation of the CMS 95% ditau exclusion region and projections of Scenario 2 for Run 3 of the LHC added; v4: minor tweaks and some updated references; version accepted for publication in Physical Review D; v5: two additional references added