Dipankar Das
In a two Higgs-doublet model with $D_4$ flavor symmetry, we establish a relation between $\tanβ$ and the Cabibbo angle. Due to a small number of parameters, the quark Yukawa sector of the model is very predictive. The flavor changing neutral currents are small enough to allow for relatively light nonstandard scalars to pass through the flavor constraints.
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The remarkable role of the vector-like quark doublet in the Cabibbo angle and $W$-mass anomalies
研究指出，一个质量为几TeV的矢量型$SU(2)_L$夸克二重态与轻夸克及顶夸克混合，可同时解释CKM第一行幺正性破坏和$W$玻色子质量偏移反常，且不与电弱观测量冲突，有望在未来对撞机中探测。
In a simplified renormalizable model where the neutrinos have PMNS (Pontecorvo-Maki-Nakagawa-Sakata) mixings tan$^{2} θ_{12} = {1/2}, θ_{13}=0, θ_{23} = π/4$ and with flavor symmetry $T^{'}$ there is a corresponding prediction where the quarks have CKM (Cabibbo-Kobayashi-Maskawa) mixings tan$2 Θ_{12} = \frac{\sqrt{2}}{3}, Θ_{13}=0, Θ_{23} =0$.
We present a framework to generate the quark mass hierarchies and mixing angles by extending the Standard Model with one extra Higgs doublet. The charm and strange quark masses are generated by small quantum effects, thus explaining the hierarchy between the second and third generation quark masses. All the mixing angles are also generated by small quantum effects: the Cabibbo angle is generated at zero-th order in perturbation theory, while the remaining off-diagonal entries of the Cabibbo-Kobayashi-Maskawa matrix are generated at first order, hence explaining the observed hierarchy $|V_{ub}|…
We study all implementations of the $S_3$ symmetry in the two Higgs doublet model with quarks, consistent with non-zero quark masses and a Cabibbo-Kobayashi-Maskawa (CKM) matrix which is not block diagonal. We study the impact of the various soft-breaking terms and vacuum expectation values, and find an interesting relation between $α$ and $β$. We also show that, in this minimal setting, only two types of assignments are possible: either all field sectors are in singlets or all field sectors have a doublet.
We explore the generation of fermion masses and quark mixing angles within flavored gauge mediation models of supersymmetry breaking in which the Higgs and messenger doublets are connected by a discrete non-Abelian symmetry. In this framework, the Higgs-messenger symmetry, which we take for concreteness to be the discrete group $\mathcal{S}_3$, also plays the role of a (partial) family symmetry. We investigate mechanisms for generating mass hierarchies for the lighter quark generations and generating the Cabibbo angle within this class of models. While perturbations of the couplings at the ren…
Maximally extending the Higgs sector of the Glashow-Salam-Weinberg model by including all scalar and pseudoscalar J=0 states expected for 2 generations of quarks, I demonstrate that the Cabibbo angle is given by tan^2(theta_c) = (1/m_K^2-1/m_D^2)/(1/m_π^2-1/m_{D_s}^2) \approx (m_π^2 /m_K^2)(1-m_K^2/m_D^2 + m_π^2/m_{D_s}^2).
We study the implications of the LHC heavy neutral Higgs search data on the aligned two Higgs doublet model with softly broken $Z_2$ symmetry. When $\tanβ$ is small, the gluon fusion production of the heavy CP-even scalar $H^0$ or the CP-odd scalar $A^0$ becomes large enough to constrain the model by the current $γγ$, $τ^+τ^-$, and $t\bar{t}$ data. By reinvestigating this small $\tanβ$ region, we find that the indirect constraints like $Δρ$, $b\to s γ$, $ΔM_{B_d}$, $R_b$, $ε_K$, and the perturbativity of running top Yukawa coupling are rather weak to be $\tanβ> 0.5$. The current heavy Higgs se…
Flavour Invariants of the N Higgs Doublet Model
本文提出分析N个双态模型味数部分的系统方法，引入混合矩阵描述基底旋转，首次提出弱基底变换不变的味数矩阵迹，对研究正规化群演化的相关物理参数具有重要意义。
In the most general two-Higgs-doublet model (2HDM), there is no distinction between the two complex hypercharge-one SU(2) doublet scalar fields, Phi_a (a=1,2). Thus, any two orthonormal linear combinations of these two fields can serve as a basis for the Lagrangian. All physical observables of the model must therefore be basis-independent. For example, tan(beta)=<Phi_2^0>/<Phi_1^0> is basis-dependent and thus cannot be a physical parameter of the model. In this paper, we provide a basis-independent treatment of the Higgs sector with particular attention to the neutral Higgs boson mass-eigensta…
Current interpretations of the LHC results on two Higgs doublet models (2HDM) underestimate the sensitivity due to neglecting higher order effects. In this work, we revisit the impact of these effects using the current cross-section times branching ratio limits of the $A\to hZ, H \to VV$ and $H\to hh$ channels. With a degenerate heavy Higgs mass $m_Φ$, we find that the LHC searches gain sensitivity to the small $\tanβ$ region after including loop corrections, even close to $\cos(β-α)=0$ which is not reachable at tree level for all types of 2HDM. For a benchmark point with $m_Φ=300$ GeV, $\tanβ…
We study constraints on type-II two Higgs doublet models at large tan{beta} from LEP/SLD Z-pole data and from lepton universality violation in W decay. We perform a global fit and find that, in the context of Z decay, the LEP/SLD experimental values for lepton universality violation, R_b, and A_b all somewhat disfavor the model. Contributions from the neutral Higgs sector can be used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions from the charged Higgs sector allow us to constrain the charged Higgs mass. For tan{beta}=100 we obtain the 1 sigma classical (Bayesian) bo…
We study the "lepton-specific" two Higgs doublet model, in which one doublet Phi_l gives mass to charged leptons and the other Phi_q gives mass to both up- and down-type quarks. We examine the existing experimental constraints on the charged Higgs boson mass and the parameter tan(beta) \equiv <Phi_q^0>/<Phi_l^0>. The most stringent constraints come from LEP-II direct searches and lepton flavour universality in tau decays. The former yields M_H+ \geq 92.0 GeV; the latter yields two allowed regions, 0.61 tan(beta) GeV \leq M_H+ \leq 0.73 tan(beta) GeV or M_H+ \geq 1.4 tan(beta) GeV, and excludes…
We study the deep inelastic process $ν_τ + {\cal N} \to τ^{-} + X$ (with ${\cal N} \equiv (n+p)/2$ an isoscalar nucleon), in the context of the two Higgs doublet model {\it type two} (2HDM(II)). In particular, we discuss the contribution to the total cross section of diagrams, in which a charged Higgs boson is exchanged. We show that for large values of $\tanβ$ such contribution for an inclusive dispersion generated through the collision of an ultrahigh energy tau-neutrino on a target nucleon can reach up to 57% of the value of the contribution of the $W^+$ exchange diagrams (i.e. can reach up…
A definite relative phase and amplitude exists between the doubly-Cabibbo-% suppressed amplitude for $D^0 \to \ko M^0$ and the Cabibbo-favored amplitude for $D^0 \to \ok M^0$, where $M^0 = (π^0,η,η')$: $A(D^0 \to \ko M^0) = - \tan^2 θ_C A(D^0 \to \ok M^0)$. Here $θ_C$ is the Cabibbo angle. This relation, although previously recognized (for $M^0 = π^0$) as a consequence of the U-spin subgroup of SU(3), is argued to be less sensitive to corrections involving SU(3) breaking than related U-spin relations involving charged kaons or strange $D$ mesons. A corresponding relation between $D^+ \to \ko π…
We calculate the new physics contributions to the neutral $B_d^0$ and $B_s^0$ meson mass splitting $ΔM_d$ and $ΔM_s$ induced by the box diagrams involving the charged-Higgs bosons in the top quark two-Higgs doublet model (T2HDM). Using the precision data, we obtain the bounds on the parameter space of the T2HDM: (a) for fixed $M_H=400$ GeV and $δ=[0^\circ,60^\circ]$, the upper bound on $\tanβ$ is $\tan β\leq 30$ after the inclusion of major theoretical uncertainties; (b) for the case of $\tanβ \leq 20$, a light charged Higgs boson with a mass around 300 GeV is allowed; and (c) the bounds on $\…
The electric dipole moment of the muon ($d_μ$) is evaluated in a two Higgs doublet model with a softly broken discrete symmetry. The leading contributions from both one loop and two loop diagrams are considered. For $\tanβ\equiv |v_2|/|v_1|$ close to one, contributions from two loop diagrams involving the $t$ quark and the $W$ boson dominate; while for $\tanβ\agt 10$, contributions from two loop diagrams involving the $b$ quark and the $τ$ lepton are dominant. In these two regions, $d_μ\approx (m_μ/m_e) d_e$. For $8 \agt \tanβ\agt 4$, significant cancellation occurs among the contributions fro…
We establish the potential existence of natural relations between the Cabibbo angle and the quark mass ratios, in a Standard Model with one Higgs doublet and two quark generations. The argument is based on the calculation of the divergent one-loop radiative corrections to the quark mass matrices.
The rare k+--->pi+ ν\barν decay is investigated in the context of type II two-Higgs-doublet model (2HDM). By using the existing experimental data of the branching ratio, restrictions on the free parameters of the model m_H, and tanβare obtained: tanβbelong to the range 0.7- o.8, and m_H belong to the range 500- 700 GeV.
The radiative B ->τ^+ τ^- γdecay is investigated in the framework of the two Higgs doublet model . The dependence of the differential branching ratio on the photon energy and the branching ratio on the two Higgs doublet model parameters, m_{H^\pm} and \tan β, are studied. It is shown that there is an enhancement in the predictions of the two Higgs doublet model compared to the Standard model case. We also observe that contributions of neutral Higgs bosons to the decay are sizable when \tanβis large.
We compute the branching fractions of B_{s,d} -> l+ l- in the type-II two-Higgs-doublet model with large tan(beta). We find that the parameters of the neutral Higgs sector of the two-Higgs-doublet model cancel in the result, so that the branching fractions depend only on the charged Higgs mass and tan(beta). For large values of tan(beta) and a charged Higgs mass above the bound from b -> s gamma, we find that the branching fractions can be enhanced by up to an order of magnitude or suppressed by up to a factor of two compared to the Standard Model result. We point out that previous calculation…
We establish the existence of one-loop finite relations between the Cabibbo angle and the quark mass ratios, in the Standard Model with one Higgs doublet and two quark generations. Assuming a simple quark-lepton universality, we use the recent SNO results to predict the two-flavour mass spectrum of the neutrinos.
Scrutinizing the Mass Matrices in Three-Higgs-Doublet Models with Generalized CP Symmetries
研究具有软破缺广义CP对称性的三希格斯二重态模型，通过构建基变换和数值拟合减少可行模型集，发现该模型能重现夸克质量和混合，22个不等价模型与实验数据兼容，为标准模型扩展及味现象学研究提供框架。
Neutron Electric Dipole Momento in Two-Higgs-Doublet Model
在双Higgs偶极子模型中研究了色电偶极矩对中子电偶极矩的影响。在$\tan\b\gg 1$、$\tan\b\ll 1$和$\tan\b\simeq 1$的情况下，研究了Weinberg算子$O_{3g}=GG\t G$和算子$O_{qg}=\bar qσ\t Gq$.由于两个轻希格斯标量交换的破坏性贡献，中子EDM大大减少。
The ratio of the vacuum expectation value of the two Higgs doublets, tan(beta), is an important parameter of the general 2-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric extension of the Standard Model (MSSM). The expected uncertainty on the determination of tan(beta) at a Linear Collider (LC) of at least 500 GeV center-of-mass energy and high luminosity is reviewed based on studies of neutral and charged Higgs boson production.
Naturally Large Tan $β$
我们表明，如果只有两个希格斯双峰的超对称标准模型，大$\tanβ$需要微调的拉格朗日阶（$1/\tanβ$），这不能解释任何近似对称的参数。有了扩展的希格斯扇区，大的$\tanβ$可以是自然的。我们给出了一个明确的例子，其中有四个双峰，它是可能实现大的$\tanβ$作为一个近似对称的结果，没有任何轻超伙伴。近似对称性可以推广到解释夸克质量矩阵中的所有层次。
We confront the Two-Higgs-Doublet Model with a variety of experimental constraints as well as theoretical consistency conditions. The most constraining data are the \bar B\to X_sγdecay rate (at low values of M_{H^\pm}), and Δρ(at both low and high M_{H^\pm}). We also take into account the B\bar B oscillation rate and R_b, or the width Γ(Z\to b\bar b) (both of which restrict the model at low values of \tanβ), and the B^-\toτν_τdecay rate, which restricts the model at high \tanβand low M_{H^\pm}. Furthermore, the LEP2 non-discovery of a light, neutral Higgs boson is considered, as well as the mu…
We discuss the Yukawa coupling unification, a very interesting prediction of the grand unified theory, in the context of scenarios with more than one pair of Higgs doublet since the current LHC constraint has become a problem for the Yukawa unification scenarios with just one pair of Higgs doublet. More than one pair of Higgs doublets can easily arise in missing partner mechanism which solves the doublet-triplet splitting problem. In such a scenario, the Yukawa unification occurs at a medium $\tanβ$ value, e.g., $\sim$ 30, which corresponds to much smaller threshold corrections compared to usu…
We propose a class of the two Higgs doublet Standard models (SMs) with a SM singlet and a class of supersymmetric SMs with two pairs of Higgs doublets, where the right-handed up/charm quarks and the right-handed top quark have different quantum numbers under extra discrete symmetries. Thus, the right-handed up and charm quarks couple to one Higgs doublet field, while the right-handed top quark couples to another Higgs doublet. The quark CKM mixings can be generated from the down-type quark sector. As one of phenomenological consequences in our models, we explore whether one can accommodate the…
CP violation in semileptonic top-quark decay is investigated by exactly using one charged- and three neutral-Higgs bosons obtained by solving the Higgs mass matrix in two-Higgs doublet model. The CP-violating up-down asymmetry of leptons from $W$ boson decays is shown to be $1 \times 10^{-4} - 4 \times 10^{-3}$ for the region of ${\rm tan} β\ll 1$, where ${\rm tan} β$ is the ratio of vacuum expectation values for the two neutral Higgs bosons.
$b \rightarrow s γ$ and $ε_b$ Constraints on Two Higgs Doublet Model
我们进行了两个严格的限制2希格斯双重模型的组合分析，一个来自最近宣布的CLEO II约束$B(b \rightarrow s γ)$和其他从最近的LEP数据$ε_b$。我们在模型中包括了从$Z \rightarrow b \overline b$到$ε_b$的单圈顶点校正。我们发现新的$ε_b$约束排除了$90\%$ C中大部分不太吸引人的窗口$\tanβ\lsim 1$。~ L.对于$m_t=150\GeV$。我们还发现，虽然$b \rightarrow s γ$约束是强的$\tanβ>1$，$ε_b$约束是强的$\tanβ\lsim 1$，因此这两个是最强的和互补的约束存在于带电的希格斯部门的模型。
Tree-level unitarity constraints on the masses of the Higgs bosons in the general Two Higgs Doublet Model (THDM) are studied. We first consider the case where the Higgs potential is invariant under a discrete symmetry transformation, and derive strong constraints on the mass of the lightest CP-even Higgs boson ($M_h$) as a function of $\tanβ$. We then show that the inclusion of the discrete symmetry breaking term weakens the mass bounds considerably. It is suggested that a measurement of $M_h$ and $\tanβ$ may enable discrimination between the two Higgs potentials.
The Two-Higgs-Doublet Model is considered, in its CP-non-conserving version. It is shown quantitatively how vacuum stability and tree-level unitarity in the Higgs-Higgs-scattering sector constrain the parameter space of the model. In particular, at high values of tanbeta, the model violates unitarity, unless some of the Higgs bosons are heavy. In the regime of large CP violation in the neutral-Higgs-t-quark sector, which requires tanbeta lsim 1, the Yukawa coupling parameter space (determined by the neutral-Higgs-sector rotation matrix) is reasonably unconstrained. On the other hand, the corre…
The Higgs boson mass spectrum and couplings of neutral Higgs bosons to fermions are worked out i n a CP spontaneously broken two Higgs doublet model in the large tan$β$ case. The differential branching ratio, forward-backward asymmetry, CP asymmetry and lepton polarization for $B\to X_s l^+ l^-$ are computed. It is shown that effects of neutral Higgs bosons are quite significant when $\tanβ$ is large. Especially, the CP violating normal polarization $P_N$ can be as large as several percents.
The feasibility of measuring the Higgs-boson properties at the Photon Collider at TESLA has been studied in detail for masses between 200 and 350 GeV, using realistic luminosity spectra and detector simulation. We consider the Two Higgs Doublet Model (II) with SM-like Yukawa couplings for h, parametrized by only one parameter (tan(beta)). The combined measurement of the invariant-mass distributions in the ZZ and W+W- decay-channels is sensitive to both the two-photon width Gamma_{gamma gamma} and phase Phi_{gamma gamma}. From the analysis including systematic uncertainties we found out that af…
Unitarity constraints on the scalar parameters both for the Standard Model and the general Two Higgs Doublet Model (THDM) are examined. In the case of the THDM with an exact discrete symmetry transformation, we show that the mass of the lightest CP-even Higgs boson ($M_h$) and $\tanβ$ are strongly correlated and consequently a strong lower bound can be put on $M_h$ for large $\tanβ$. It is also shown that the inclusion of the discrete symmetry breaking term relaxes the aforementioned correlation.
Electroweak Z-string in Two-Higgs-Doublet Standard Model
我们导出了具有两个Higgs双峰的Glashow-Weinberg-Salam模型的电弱Z弦解。这种解的存在特别需要两个希格斯真空期望值之比{ \it，即}之间的特定关系。$\tanβ$和希格斯势中的耦合。
The most commonly used parameterizations of the Yukawa couplings in the two Higgs doublet model are revisited. Their similitudes and differences are emphasized and relations between the different notations used in the literature are derived. Using these relations, bounds on the space of parameters of the charged Higgs sector of the two Higgs doublet model are obtained. These constraints are obtained from flavor observables like the measurement of B -> Xs γand the recent measurement of Bs -> μ+ μ- from LHCb. The ratio R_{H+}=B(H+ -> τ^+ ν_τ)/B(H+ -> t b) is evaluated for the two Higgs doublet m…
We calculate Yukawa corrections of order $α_{ew} M_t^2/M_W^2$ to single top quark production via $q \bar q'\rightarrow t \bar b$ at the Fermilab Tevatron in the two-Higgs-doublet models. In our calculation we also keep the terms proportional to $ M_b^2 \tan^2 β$ since their effects may become rather important for large $\tanβ$. The corrections can amount to more than a 15\% reduction in the production cross section relative to the tree level result in the general two-Higgs-doublet model, and a 10\% enhancement in the minimal supersymmetric model, which might be observable at a high-luminosity …
Using the experimental data on meson decay rates, mixing and CP violation we set competitive upper and lower limits to the parameter tan(beta) as a function of the mass of the charged Higgs m_H in the Two Higgs Doublet Model (Model II).
We show that the Cabibbo angle theta\_c satisfies the relation tan(2 theta\_c)=-+/- 1/2 when universality for diagonal neutral currents of mass eigenstates is satisfied at the same level of accuracy as the absence of their off-diagonal counterparts. The predicted value is cos theta\_c \approx 0.9732, only 7/10000 away from experimental results. No mass ratio appears in the calculation. theta\_c occurs a priori for both quark species, and, showing that one recovers the standard dependence of leptonic and semi-leptonic decays of pseudoscalar mesons, we advocate, like for neutrinos and charged le…
We consider a CP-conserving two-Higgs-doublet type II model with a light scalar or pseudoscalar neutral Higgs boson ($\h=\hl$ or $\h=\ha$) that has no $ZZ/WW$ coupling and, thus, cannot be detected in $\epem\to Z\h$ (Higgs-strahlung) or $ν\antiν\h$ (via $WW$ fusion). Despite sum rules which ensure that the light $\h$ must have significant $t\anti t$ or $b\anti b$ coupling, for a wedge of moderate $\tanb$, that becomes increasingly large as $\mh$ increases, the $\h$ can also escape discovery in both $b\anti b \h$ and $t\anti t \h$ production at a $\rts=500-800\gev$ $\epem$ collider (for expecte…
The recent measurement on the muon anomalous magnetic moment $a_μ$ shows a $2.6σ$ deviation from the standard model value. We show that it puts strong constraints on the parameter space of the two-higgs doublet model (2HDM) II. The dominant contribution of the Higgses comes at the two-loop level, and in order to explain the data it favors a pseudoscalar $A$ with a light mass range and a large $\tanβ$. At 95% C.L., upper limit for $m_{\scriptscriptstyle A}$ is $29 (55) (85)$ GeV for $\tanβ=30 (45) (60)$, and $\tan β$ is bounded below at 17. This is in sharp contrast to the conclusion one draws …
Neutron Electric Dipole Moment in Two Higgs Doublet Model
研究了双Higgs二重态模型中色电偶极矩对中子电偶极矩的影响。本文系统地研究了Weinberg算子$O_{3g}=GG\t G$和算子$O_{qg}=\bar qσ\t Gq$，并给出了$\tan\b\gg 1$、$\tan\b\ll 1$和$\tan\b\simeq 1$的例子.结果表明，与其它算符相比，$O_{sg}$对中子EDM的贡献最大，而$O_{ug}$和$O_{3g}$的贡献相互抵消.指出在最轻的中性Higgs标量之外加入第二轻的中性Higgs标量对估算中子EDM是至关重要的。当两个希格斯标量的质量差为$O(50\G)$量级时，由于相互的破坏性贡献，中子的EDM大大减小。
Due to the large mass of top quark, CP violation in the top-quark decay is sensitive to the interactions mediated by Higgs bosons. We consider CP violation in $t\rightarrow W^+ b$ decay by calculating consistently in unitary gauge the CP-violating up-down asymmetry of the leptons from $W$ boson decays in $t\rightarrow W^+ b$, defined by Grzcadkowski and Gunion, in the two-Higgs doublet model with CP-violating neutral sector. The asymmetry is shown to be at most of the order of $(1-3)\times 10^{-4}$ for $\tanβ=1.0$, where $\tanβ$ is the ratio of vacuum expectation values for the two neutral Hig…
The type X (lepton-specific) two-Higgs-doublet model at large $\tanβ$ becomes leptophilic and thus allows a light pseudoscalar $A$ accommodating the observed muon $g-2$ deviation without conflicting with various hadronic constraints. On the other hand, it is strongly constrained by leptonic precision observables such as lepton universality test in the neutral and charged currents. Treating all the lepton universality data in a consistent way, we show how the current data constrain the parameter space of $m_A$ and $\tanβ$ for given degenerate masses of heavy Higgs bosons $H$ and $H^\pm$. While …
Radiative Electroweak Breaking with Pseudogoldstone Higgs Doublets
我们考虑了一个基于$SU(3)_c \times SU(3)_L \times SU(3)_R$的超对称大统一的现实例子，其中电弱（EW）希格斯偶态是“轻”的“伪金石”机制的结果。我们讨论了辐射EW打破在这个模型中，探索特别是“小”（为了统一）和“大”$(\approx m_t/m_b)$ $\tan β$地区通过研究的变化$r (\equiv \sqrt{μ^2_{1,2}/μ^2_3})$，其中$μ^2_{1,2,3}$是众所周知的MSSM参数在大统一尺度评估。当$r$足够接近于1时，量$\tan β$可以是1阶，但反过来并不总是正确的。
The production process of the charged Higgs-boson associated with a $W$ boson at electron-positron colliders is discussed in the two-Higgs-Doublet Model (2HDM) and in the Minimal Supersymmetric Standard Model (MSSM). The process is induced at one-loop level in these models. We examine how much the cross section can be enhanced by quark- and Higgs-loop effects. In the non-SUSY 2HDM, in addition to large top-bottom ($t$-$b$) loop effects for small $\tan β$ ($\ll \sqrt{m_t/m_b}$), the Higgs-loop diagrams can contribute to the cross section to some extent for moderate $\tan β$ values. For larger $…
$B \rightarrow τνX$ decays in a two Higgs doublet model
利用重夸克展开和算子乘积展开计算了两Higgs偶重态模型中包含$B \rightarrow τνX$衰变的衰变率.结合最近对Br（$B \ra τνX$）的测量，我们发现了一个极限值$\tan β< 0.58 m_H/\mbox{GeV}$为90% C. L.
We show that inclusion of a single generation of vector-like leptons in the Two-Higgs Doublet Models significantly enlarges the allowed parameter space consistent with the muon anomalous magnetic moment, as well as with other theoretical and experimental constraints. While previously $(g -2)_μ$ could only be resolved in Type-X scenario by requiring a light pseudoscalar Higgs boson and large $\tan β$, contributions of vector-like leptons via two-loop Barr Zee diagrams broaden the allowed parameter space, allowing $\tan β$ as low as 10 and pseudoscalar masses as large as $\cal{O}$(1 TeV) while f…
In the two Higgs doublet model, $\tanβ$ is an important parameter, which is defined as the ratio of the vacuum expectation values of the doublets. We study how accurately $\tanβ$ can be determined at linear colliders via the precision measurement of the decay branching fraction of the standard model (SM) like Higgs boson. Since the effective coupling constants of the Higgs boson with the weak gauge bosons are expected to be measured accurately, the branching ratios can be precisely determined. Consequently, $\tanβ$ can be determined with a certain amount of accuracy. Comparing the method to th…
We calculate the cross section for e+e- --> H+ e- nubar in the two-Higgs-doublet model from one-loop diagrams involving top and bottom quarks. This process offers the possibility of producing the charged Higgs boson at the e+e- collider when its mass is more than half the center-of-mass energy, so that charged Higgs pair production is kinematically forbidden. The cross section receives contributions from both s-channel and t-channel processes; the s-channel contribution dominates for center-of-mass energies of 1 TeV and below. About 80% of the s-channel contribution comes from the resonant pro…
We discuss lepton flavor violation (LFV) associated with tau leptons in the framework of the two-Higgs-doublet model. Current data for rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large $\tanβ$ region where $\tanβ$ is the ratio of vacuum expectation values of the two Higgs doublets. We show that measuring the LFV Higgs boson decays $h \to τ^\pm μ^\mp$ at future colliders can be useful to further constrain the LFV couplings especially in the relatively small $\tanβ$ region.
We study the possible existence of a real Cabibbo-Kobayashi-Maskawa (CKM) matrix, with CP violation originating from physics beyond the standard model (SM). We show that present experimental data allow for a real CKM matrix provided that new physics also contributes to Delta m_{B_d} by at least 20% of the SM contribution (for rho > 0), besides generating CP violation in the kaon sector. The naturalness of a real CKM matrix is studied within the framework of general multi-Higgs-doublet models with spontaneous CP violation. As an example, we discuss a specific two-Higgs-doublet model and its imp…
We study the Two Higgs Doublet Model of type II, set limits to the parameter $\tanβ$ as a function of the mass of the charged Higgs $m_{H}$, and find interesting discovery channels in hadron colliders or muon colliders. We also obtain the running coupling constants and discuss Grand Unification. A dissertation submitted to the University of San Francisco-Quito in partial fulfillment of the requirements for the degree of Doctor of Phylosophy.
In extensions of the Standard Model with two Higgs doublets, flavour changing Yukawa couplings of the neutral scalars may be present at tree level. In this work we consider the most general scenario in which those flavour changing couplings are absent. We re-analyse the conditions that the Yukawa coupling matrices must obey for such \emph{general flavour conservation} (gFC), and study the one loop renormalisation group evolution of such conditions in both the quark and lepton sectors. We show that gFC in the leptonic sector is one loop stable under the Renormalization Group Evolution (RGE) and…
We analyze the unconventional top quark decay mode t -> H^+ b at the quantum level within the context of general Two-Higgs-Doublet models by including the full electroweak effects from the Yukawa couplings. The results are presented in the on-shell renormalization scheme with a physically well motivated definition of tan(beta). While the QCD corrections have been taken into account in the current experimental analyses of that decay, the electroweak effects have always been neglected. However, we find that they can be rather large and could dramatically alter the interpretation of the present d…
We discuss phenomenological consequences of requiring the cancellation of one-loop quadratic divergences in corrections to scalar masses within Two-Higgs-Doublet Models (2HDM). It is shown that the Inert Doublet Model (IDM) can not accommodate the requirement of the cancellation. A general 2HDM is also analyzed taking into account existing experimental constraints. Allowed regions in the parameter space, permitting the above cancellation, are determined. A degeneracy between masses of scalar bosons is observed for tanbeta \gsim 40. The possibility for CP violation in the scalar potential is di…
The radiative leptonic $B_{c}\toτ\bar{ν_τ}γ$ decay is analysed in context of 2HDM. It is shown that with large values of $tanβ$, the contributions of Model II to the decay rate exceeds considerably the Standard Model ones, while the contributions of Model I overlap with the Standard Model predictions.
We calculate Higgs production cross sections at a muon collider in the Two Higgs Doublet Model of type II. The most interesting productions channels are mu^- mu^+ --> h^0 Z^0, H^0 Z^0, H^- H^+, A^0 Z^0 and H^{-/+} W^{+/-}. The last channel is compared with the production processes p pbar --> H^{-/+} W^{+/-} X and p p --> H^{-/+} W^{+/-} X at the Tevatron and LHC energies, respectively, for large values of tan(beta).
Many extensions of the Standard Model involve two Higgs doublet fields to break the electroweak symmetry, leading to the existence of three neutral and two charged Higgs particles. In particular, this is the case of the Minimal Supersymmetric extension of the Standard Model, the MSSM. A very important parameter is $\tanβ$ defined as the ratio of the vacuum expectation value of the two Higgs doublets. In this paper we focus on the left-right asymmetry in the production of polarised top quarks in association with charged Higgs bosons at the LHC. This quantity allows for a theoretically clean det…
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