Study of the Relation Between Charged Yukawa Coupling Constants Under the Leptonic Specific Two Higgs Doublet Model

A pattern of deviations in the Standard Model (SM) like Higgs boson (h) couplings from their SM predictions depends on the structure of the Higgs sector and the Yukawa interaction. In particular, in Two Higgs Doublet Models (THDMs) with a softly-broken Z2 symmetry, different characteristic patterns of deviation in Yukawa coupling constants (hff‾) can be allowed depending on four types of Yukawa interactions. We calculate hff‾ coupling constants at the one-loop level in all the types of THDMs. Even if there is no deviation in the hff‾ couplings at the tree level, they can deviate from the SM predictions by a few percent due to extra Higgs boson loop contributions. We find that if the deviations in the gauge couplings hVV(V=Z,W) are found with an enough large to be measured at the International Linear Collider (ILC), the scale factors for the hff‾ couplings do not overlap among the THDMs with four types of Yukawa interactions even taking into account the radiative corrections. Therefore, in such a case, we can indirectly determine the type of the THDMs at the ILC even without information from direct searches of the additional Higgs bosons.

We calculate one-loop corrected Yukawa coupling constants hff¯ for the standard model-like Higgs boson h in two Higgs doublet models. We focus on the models with the softly-broken Z2 symmetry, which is imposed to avoid the flavor changing neutral current. Under the Z2 symmetry, there are four types of Yukawa interactions. We find that one-loop contributions from extra Higgs bosons modify the hff¯ couplings to be maximally about 5% under the constraint from perturbative unitarity and vacuum stability. Our results show that the pattern of tree-level deviations by the mixing effect in each type of Yukawa couplings from the SM predictions does not change even including radiative corrections. Moreover, when the gauge couplings hVV (V=W,Z) are found to be slightly (with a percent level) different from the SM predictions, the hff¯ couplings also deviate but more largely. Therefore, in such a case, not only can we determine the type of Yukawa couplings but also we can obtain information on the extra Higgs bosons by comparing the predictions with precisely measured hff¯ and hVV couplings at future electron–positron colliders.

After the discovery of the standard model-like Higgs boson at the LHC, the structure of the Higgs sector remains unknown. We discuss how it can be determined by the combination of direct and indirect searches for additional Higgs bosons at future collider experiments. First of all, we evaluate expected excluded regions for the mass of additional neutral Higgs bosons from direct searches at the LHC with the 14 TeV collision energy in the two Higgs doublet models with a softly broken ${Z}_{2}$ symmetry. Second, precision measurements of the Higgs boson couplings at future experiments can be used for the indirect search of extended Higgs sectors if the measured coupling constant with the gauge boson slightly deviates from the standard model value. In particular, in the two Higgs doublet model with the softly broken discrete symmetry, there are four types of Yukawa interactions, so that they can be discriminated by measuring the pattern of deviations in Yukawa coupling constants. Furthermore, we can fingerprint various extended Higgs sectors with future precision data by detecting the pattern of deviations in the coupling constants of the standard model-like Higgs boson. We demonstrate how the pattern of deviations can be different among various Higgs sectors that predict the electroweak rho parameter to be unity, such as models with additional an isospin singlet, a doublet, triplets, or a septet. We conclude that, as long as the gauge coupling constant of the Higgs boson slightly differs from the standard model prediction but is enough to be detected at the LHC and its high-luminosity run or at the International Linear Collider, we can identify the nonminimal Higgs sector even without direct discovery of additional Higgs bosons at the LHC.

In the left-right symmetric model based on $SU(2)_L\\times SU(2)_R\\times\nU(1)_{B-L}$ gauge symmetry, there appear heavy neutral scalar particles\nmediating quark flavor changing neutral currents (FCNCs) at tree level. We\nconsider a situation where such FCNCs give the only sign of the left-right\nmodel while $W_R$ gauge boson is decoupled, and name it "semi-aligned two Higgs\ndoublet model" because the model resembles a two Higgs doublet model with\nmildly-aligned Yukawa couplings to quarks. We predict a correlation among\nprocesses induced by quark FCNCs in the model, and argue that future precise\ncalculation of meson-antimeson mixings and CP violation therein may hint at the\nsemi-aligned two Higgs doublet model and the left-right model behind it.\n

We discuss the realization of two Higgs doublets model in the framework of 6 dimensional Gauge-Higgs Unification model with a simple Lie group G_M. Two Higgs SU(2)_L doublets can emerge at the low energy effective theory, and the quartic coupling terms in the scalar potential, essential for the electroweak symmetry breaking, are now G_M gauge invariant and permissive. A realistic two Higgs doublets model can possibly be obtained only when two of the root vectors associated with the would-be Higgs doublets and the root vector for SU(2)_L form an isosceles triangle with vertex angle either of Pi/3, Pi/2, or 2Pi/3. Moreover, depending on G_M, the scalar potential of resulting two Higgs doublets model can admit only a few limited forms. The mass spectrum of the physical Higgs and the weak mixing angle are briefly discussed.

We characterize models where electroweak symmetry breaking is driven by two light Higgs doublets arising as pseudo-Nambu–Goldstone bosons of new dynamics above the weak scale. They represent the simplest natural two Higgs doublet alternative to supersymmetry. We construct their low-energy effective Lagrangian making only few specific assumptions about the strong sector. These concern their global symmetries, their patterns of spontaneous breaking and the sources of explicit breaking. In particular we assume that all the explicit breaking is associated with the couplings of the strong sector to the Standard Model fields, that is gauge and (proto)-Yukawa interactions. Under those assumptions the scalar potential is determined at lowest order by very few free parameters associated to the top sector. Another crucial property of our scenarios is the presence of a discrete symmetry, in addition to custodial SO(4), that controls the T-parameter. That can either be simple CP or a Z 2 that distinguishes the two Higgs doublets. Among various possibilities we study in detail models based on SO(6)/SO(4) × SO(2), focussing on their predictions for the structure of the scalar spectrum and the deviations of their couplings from those of a generic renormalizable two Higgs doublet model.

We show that the rate for di-Higgs production at the LHC can be enhanced by a factor as large as 25 compared to the Standard Model value in the two Higgs doublet model, while being consistent with the known properties of the observed Higgs boson h. There are correlated modifications in toverline{t}h and resonant Zh production rates, which can serve as tests of this model. Our framework treats both Higgs doublets on equal footing, each with comparable Yukawa couplings to fermions. The Cheng-Sher ansatz for multi-Higgs doublet model is shown to be strongly disfavored by current experiments. We propose a new ansatz for the Yukawa couplings of the Higgs doublets Φa is proposed, where Yij(a) = Cij(a) · min{mi, mj}/v, with Cij(a) being order one coefficients, mi the mass of fermion i and v the electroweak vacuum expectation value. Such a pattern of couplings can explain the observed features of fermion masses and mixings and satisfies all flavor violation constraints arising from the exchange of neutral Higgs bosons. The rate for μ → eγ decay and new contributions to CP violation in {B}_s-{overline{B}}_s mixing are predicted to be close to the experimental limits.

Mixing of the TeV‐scals flavon fields with the electroweak Higgs bosons of the Two Higgs Doublet Model, could induce large Flavor Changing Neutral Curretns (FCNC), interactions which can be tested both at low and high energy experiments. We construct a model of this kind, that involves the Froggart‐Nielsen mechanism that TeV‐scals flavon field, which mixes with a Two Higgs doublet model and explore its phonomenology.

The W-width in the two Higgs doublet model

We study the electric and chromo electric dipole moment of top quark in the general two Higgs Doublet model (model III). We analyse the dependency of this quantity to the new phases coming from the complex Yukawa couplings and masses of charged and neutral Higgs bosons. We observe that the electric and chromo elecric dipole moments of top quark are at the order of 10^{-21} e cm and 10^{-20} g_s cm, which are extremely large values compared to ones calculated in the SM and also two Higgs Doublet model with real Yukawa couplings.

Recently a gauged two Higgs doublet model, in which the two Higgs doublets are embedded into the fundamental representation of an extra local SU(2)_H group, was constructed. Both the new gauge bosons Z^prime and W^{prime (p,m)} are electrically neutral. While Z^prime can be singly produced at colliders, W^{prime (p,m)}, which is heavier, must be pair produced. We explore the constraints of Z^prime using the current Drell–Yan type data from the Large Hadron Collider. Anticipating optimistically that Z^prime can be discovered via the clean Drell–Yan type signals at a high luminosity upgrade of the collider, we explore the detectability of extra heavy fermions in the model via the two leptons/jets plus missing transverse energy signals from the exotic decay modes of Z^prime . For the W^{prime (p,m)} pair production in a future 100 TeV proton–proton collider, we demonstrate certain kinematical distributions for the two/four leptons plus missing energy signals have features distinguishable from the Standard Model background. In addition, comparisons of these kinematical distributions between the gauged two Higgs doublet model and the littlest Higgs model with T-parity, the latter of which can give rise to the same signals with competitive if not larger cross sections, are also presented.

Understanding symmetry of extended Higgs models helps to construct the theory beyond the standard model and gives important insights for testing these models by experiments. The custodial symmetry plays an important role as a leading principle to construct non-minimal Higgs sectors. On the other hand, new sources of CP violation in the Higgs sector are essentially important to explain the baryon asymmetry of the Universe. In the two Higgs doublet model, it has been known that the CP violation and the custodial symmetry are not compatible, and thus the CP violating Higgs potential in general violates the custodial symmetry in the Higgs sector. In this paper, we discuss the loop-induced H±W∓Z vertices in the two Higgs doublet model, which are induced due to the custodial symmetry violation of the sector of the particles in the loop, and study how the vertices are affected by the CP violation. We calculate the H±W∓Z vertices in the most general two Higgs doublet model with the CP violation at the one-loop level and evaluate the decay modes H± → W±Z caused by these vertices. We obtain new contributions to the H±W∓Z vertices from the CP violating part of the model, in addition to the known contributions from the CP conserving part. Moreover, we find that an asymmetry between the decays H+ → W+Z and H− → W−Z is caused by the CP violating phases in the model, some of which are important for the electroweak baryogenesis. We also briefly mention testability of these vertices at future collider experiments.

We evaluate the baryon number abundance based on the charge transport scenario of top quarks in the CP-violating two Higgs doublet model, in which Yukawa interactions are aligned to avoid dangerous flavor changing neutral currents, and coupling constants of the lightest Higgs boson with the mass 125 GeV coincide with those in the standard model at tree level to satisfy the current LHC data. In this model, the severe constraint from the electric dipole moment of electrons, which are normally difficult to be satisfied, can be avoided by destructive interferences between CP-violating phases in Yukawa interactions and scalar couplings in the Higgs potential. Viable benchmark scenarios are proposed under the current available data and basic theoretical bounds. We find that the observed baryon number can be reproduced in this model, where masses of additional Higgs bosons are typically 300–400 GeV. Furthermore, it is found that the triple Higgs boson coupling is predicted to be 35–55 % larger than the standard model value.

Hermitian flavor violation

The B-factories results provide an impressive confirmation of the Standard Model (SM) description of flavor and CP violation. Nevertheless, as more data were accumulated, deviations in the 2.5-3.5 sigma range have emerged pointing to the exciting possibility of new CP-odd phase(s) and flavor violating parameters in B-decays. Primarily this seems to be the case in the time dependent CP asymmetries in penguin dominated modes (e.g. B -> phi (eta') Ks). We discuss these and other deviations from the SM and, as an illustration of possible new physics scenarios, we examine the role of the Top Two Higgs Doublet Model. This is a simple extension of the SM obtained by adding second Higgs doublet in which the Yukawa interactions of the two Higgs doublets are assigned in order to naturally account for the large top-quark mass. Of course, many other extensions of the Standard Model could also account for these experimental deviations. Clearly if one takes these deviations seriously then some new particles in the 300 GeV to few TeV with associated new CP-odd phase(s) are needed.