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In the left-right symmetric model based on $SU(2)_Ltimes SU(2)_Rtimes U(1)_{B-L}$ gauge symmetry, there appear heavy neutral scalar particles mediating quark flavor changing neutral currents (FCNCs) at tree level. We consider a situation where such FCNCs give the only sign of the left-right model while $W_R$ gauge boson is decoupled, and name it semi-aligned two Higgs doublet model because the model resembles a two Higgs doublet model with mildly-aligned Yukawa couplings to quarks. We predict a correlation among processes induced by quark FCNCs in the model, and argue that future precise calculation of meson-antimeson mixings and CP violation therein may hint at the semi-aligned two Higgs doublet model and the left-right model behind it.
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We present the results of a global fit to the Aligned Two-Higgs Doublet Model, assuming that there are no new sources of CP violation beyond the quark mixing matrix. We use the most constraining flavour observables, electroweak precision measurements and the available data on Higgs signal strengths and collider searches for heavy scalars, together with the theoretical requirements of perturbativity and positivity of the scalar potential. The combination of all these constraints restricts the values of the scalar masses, the couplings of the scalar potential and the flavour-alignment parameters. The numerical fits have been performed using the open-source HEPfit package.
We study the Two-Higgs-Doublet Model with the aligned Yukawa sector (A2HDM) in light of the observed excess measured in the muon anomalous magnetic moment. We take into account the existing theoretical and experimental constraints with up-to-date values and demonstrate that a phenomenologically interesting region of parameter space exists. With a detailed parameter scan, we show a much larger region of viable parameter space in this model beyond the limiting case Type X 2HDM as obtained before. It features the existence of light scalar states with masses $3$ GeV $lesssim m_H^{} lesssim 50$ GeV, or $ 10$ GeV $lesssim m_A^{} lesssim 130$ GeV, with enhanced couplings to tau leptons. The charged Higgs boson is typically heavier, with $200$ GeV $ lesssim m^{}_{H^+} lesssim 630$ GeV. The surviving parameter space is forced into the CP-conserving limit by EDM constraints. Some Standard Model observables may be significantly modified, including a possible new decay mode of the SM-like Higgs boson to four taus. We comment on future measurements and direct searches for those effects at the LHC as tests of the model.
A novel model embedding the two Higgs doublets in the popular two Higgs doublet models into a doublet of a non-abelian gauge group $SU(2)_H$ is presented. The Standard Model $SU(2)_L$ right-handed fermion singlets are paired up with new heavy fermions to form $SU(2)_H$ doublets, while $SU(2)_L$ left-handed fermion doublets are singlets under $SU(2)_H$. Distinctive features of this anomaly-free model are: (1) Electroweak symmetry breaking is induced from spontaneous symmetry breaking of $SU(2)_H$ via its triplet vacuum expectation value; (2) One of the Higgs doublet can be inert, with its neutral component being a dark matter candidate as protected by the $SU(2)_H$ gauge symmetry instead of a discrete $Z_2$ symmetry in the usual case; (3) Unlike Left-Right Symmetric Models, the complex gauge fields $(W_1^{prime}mp i W_2^{prime})$ (along with other complex scalar fields) associated with the $SU(2)_H$ do {it not} carry electric charges, while the third component $W^{prime}_3$ can mix with the hypercharge $U(1)_Y$ gauge field and the third component of $SU(2)_L$; (4) Absence of tree level flavour changing neutral current is guaranteed by gauge symmetry; and {it etc}. In this work, we concentrate on the mass spectra of scalar and gauge bosons in the model. Constraints from previous $Z^prime$ data at LEP and the Large Hadron Collider measurements of the Standard Model Higgs mass, its partial widths of $gammagamma$ and $Zgamma$ modes are discussed.
We discuss two Higgs doublet models with a softly-broken discrete $mathbb{S}_3$ symmery, where the mass matrix for charged-leptons is predicted as the diagonal form in the weak eigenbasis of lepton fields. Similar to an introduction of $mathbb{Z}_2$ symmetry, the tree level flavor changing neutral current can be forbidden by imposing the $mathbb{S}_3$ symmetry to the model. Under the $mathbb{S}_3$ symmetry, there are four types of Yukawa interactions depending on the $mathbb{S}_3$ charge assignment to right-handed fermions. We find that extra Higgs bosons can be muon and electron specific in one of four types of the Yukawa interaction. This property does not appear in any other two Higgs doublet models with a softly-broken ${mathbb Z}_2$ symmetry. We discuss the phenomenology of the muon and electron specific Higgs bosons at the Large Hadron Collider; namely we evaluate allowed parameter regions from the current Higgs boson search data and discovery potential of such a Higgs boson at the 14 TeV run.
The two Higgs bi-doublet left-right symmetric model (2HBDM) as a simple extension of the minimal left-right symmetric model with a single Higgs bi-doublet is motivated to realize both spontaneous P and CP violation while consistent with the low energy phenomenology without significant fine tuning. By carefully investigating the Higgs potential of the model, we find that sizable CP-violating phases are allowed after the spontaneous symmetry breaking. The mass spectra of the extra scalars in the 2HBDM are significantly different from the ones in the minimal left-right symmetric model. In particular, we demonstrate in the decoupling limit when the right-handed gauge symmetry breaking scale is much higher than the electroweak scale, the 2HBDM decouples into general two Higgs doublet model (2HDM) with spontaneous CP violation and has rich induced sources of CP violation. We show that in the decoupling limit, it contains extra light Higgs bosons with masses around electroweak scale, which can be directly searched at the ongoing LHC and future ILC experiments.
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