multi-Higgs Doublet Models Research Articles

Transverse tau polarization in inclusive [formula omitted] decays

We calculate, in the framework of multi Higgs doublet models, the CP violating transverse tau polarization, P τ , in inclusive semileptonic B meson decays. We find that P τ diverges at O( 1 m b 2 ) of the heavy quark expansion. We discuss the physical reasons for this divergence and show how to regularize it. We find large 1 m b 2 corrections that can suppress the CP asymmetry by as much as 30%. The maximal allowed asymmetry is a c ∼ 0.34. We discuss how the allowed range is expected to change in the future.

CP-violating polarizations in semileptonic heavy meson decays.

We study the $T$-violating lepton transverse polarization ($P^\perp_l$) in three body semileptonic heavy meson decays to pseudoscalar mesons and to vector mesons. We calculate these polarizations in the heavy quark effective limit, which simplifies the expressions considerably. After examining constraints from $CP$ conserving (including $b \rightarrow s \gamma$) and $CP$ violating processes, we find that in $B$ decays, $P^\perp$ of the muon in multi-Higgs doublet models can be of order $10\%$, while $P^\perp$ of the $\tau$ can even approach unity. In contrast, $P^\perp_\mu$ in $D$ decays is at most 1.5\%. We discuss possibilities for detection of $P^\perp_l$ at current and future $B$ factories. We also show that $P^\perp_l$ in decays to vector mesons, unlike in decays to pseudoscalars, can get contributions from left-right models. Unfortunately, $P^\perp_l$ in that case is proportional to $W_L$-$W_R$ mixing, and is thus small.

CP violation in a multi higgs doublet model

We study CP violation in a multi-Higgs doublet model based on a $S_3 \times Z_3$ horizontal symmetry. We consider two mechanisms for CP violation in this model: a) CP violation due to complex Yukawa couplings; and b) CP violation due to scalar-pseudoscalar mixings. We find that the predictions for $\epsilon'/\epsilon$, CP violation in B decays and the electric dipole moments of neutron and electron are different between these two mechanisms. These predictions are also dramatically different from the minimal Standard Model predictions.

Phenomenology of models with more than two Higgs doublets

We study the most general Multi-Higgs-Doublet Model (MHDM) with Natural Flavor Conservation (NFC). The couplings of a charged scalar H i ± to up quarks, down quarks and charged leptons depend on three new complex parameters, X i , Y i , and Z i , respectively. We prove relations among these parameters. We carry out a comprehensive analysis of phenomenological constraints on the couplings of the lightest charged scalar: X, Y and Z. We find that the general MHDM may differ significantly from its minimal version, the Two-Higgs-Doublet Model (2HDM).

CP violation in a multi-Higgs-doublet model with flavor-changing neutral currents.

We study CP violation in a multi-Higgs doublet model based on a $S_3 \times Z_3$ horizontal symmetry where CKM phase is not the principal source of CP violation. We consider two mechanisms for CP violation in this model: a) CP violation due to complex Yukawa couplings; and b) CP violation due to scalar-pseudoscalar Higgs boson mixings. Both mechanisms can explain the observed CP violation in the neutral Kaon system. $\epsilon'/\epsilon$ due to neutral Higgs boson exchange is small in both mechanisms, but charged Higgs boson con- tributions can be as large as $10^{-3}$ for a), and $10^{-4}$ for b). CP violation in the neutral B system is, however, quite different from the Minimal Standard Model. The neutron Electric Dipole Moment can be as large as the present ex- perimental bound, and can be used to constrain charged Higgs boson masses. The electron EDM is one order of magnitude below the experimental bound in case b) and smaller in case a).

Multi-Higgs doublet model: Can it account for ℓ+ℓ−γγ events?

Motivated by recent experiments at LEP (Z →l+ l− γγ, withMγγ-59 GeV), we examine the possibility that such events are explained by a Bjorken process with a resonant Higgs (Mho ≏59 GeV) decaying to γγ. We investigate theN-doublet-Higgs model withoutCP violation. Under the simplifying assumption that(N-k) doublets (k≥ 1) decouple from the fermion sector, we could only explain the observed events if: i)(N- 1) ≥ 2 and ii) the masses of the corresponding(N- 1) neutral scalars are either completely or almost degenerate,i.e. the decay Z →l+l− γγ proceeds now via several overlapping resonances. Such a scenario would require fine tuning. Furthermore, the deficit of the observed decays Z → → vvγ, qqγγ (atMγγ∽59 GeV) indicates that one either has to go beyond simple extensions of the minimal standard model, or one has to wait for more experimental data.

Two-loop contributions of flavor-changing neutral Higgs bosons to micro-->e gamma.

The two--loop mechanism of Bjorken and Weinberg is used to constrain flavor changing neutral Higgs bosons. We calculate the complete set of two--loop diagrams for the rare decay $\mu \rightarrow e + \gamma$ induced by such neutral Higgs bosons, for arbitrary Higgs and top masses. The analytic result is used to set limits on Higgs masses for some recent models with specific ansatz about the flavor changing couplings. For example, in the Cheng--Sher scenario of multi-Higgs doublet models, all neutral Higgs bosons possess flavor changing ($f_i \leftrightarrow f_j)$ couplings proportional to $\sqrt{m_i m_j}$. We find that the present limit on $\mu\to e\gamma$ implies that, in such scheme, these neutral Higgs bosons should be heavier than $200$ GeV.

CP violating electron-nucleon interactions in multi-Higgs doublet and leptoquark models

CP violating electron-nucleon interactions and the resulting atomic EDM are studied in several models. In the standard model these interactions are very small and are well below the experimental upper bounds. In multi-Higgs doublet models. The four-Fermi interactions, N̄Nēγ 5e and N̄γ 5Nēe, can be quite large. In some range of parameters the contribution of these interactions to the atomic EDM can exceed the contribution of the electron EDM. In leptoquark models the contribution from the tensor interaction, N̄σ μνNēσ μνγ 5e, is the dominant one in Hg, Xe and TIF.

The strange quark contribution to the neutron electric dipole moment in multi-Higgs doublet models

In this paper we study the strange quark contribution to the neutron electric dipole moment and compare with other contributions in multi-Higgs doublet models. We find that the strange quark contribution is significant because the strange quark color dipole moment is larger than that of the down (up) quark by a factor >NU>m s m s ( m s m u ) . In the case of neutral Higgs it can be the dominant contribution to the neutron electric dipole moment.

Production of colourless scalar resonance in $$p\bar p$$ annihilation

We analyse under what conditions the production of colourless scalar resonance (Higgs boson) can be enhanced and its subsequent decays into gauge bosons and/or light Higgs bosons can provide a test for them. We discuss the expected experimental signatures and point out difficulties of obtaining large coupling to light quarks in the framework of a multi Higgs doublet model with horizontal symmetry.