We demonstrate how residual flavour symmetries, infrared signatures of symmetry breaking in complete models of flavour, can naturally forbid (or limit in a flavour specific way) flavour-changing neutral currents (FCNC) in multi-Higgs-doublet models (MHDM) without using mass hierarchies. We first review how this model-independent mechanism can control the fermionic mixing patterns of the Standard Model, and then implement the symmetries in the Yukawa sector of MHDM, which allows us to intimately connect the predictivity of a given flavour model with its ability to sequester FCNC. Finally, after discussing various subtleties of the approach, we sketch an $A_4$ toy model that realises an explicit example of these simplified constructions.
Large long-distance standard model effects in FCNC semileptonic D decays can make observable these processes in future measurements. Eventual disagreements in this sector and/or the observation of lepton family violating (LFV) D decays would require an explanatio beyond the SM framework. In this paper we confront present experimental data on leptonic and semileptonic FCNC and LFV D meson decays with a version of the two-Higgs doublet model that allows these effects to occur at tree- level. The stringent bounds on the parameters of the model are obtained from D^0 --> l^+l'^- and D --> pi l^+l'^…
We analyse a class of two Higgs doublet models where flavour-changing neutral currents (FCNC) are present at tree level in a mixing-suppressed manner. In this class of models, because of a discrete symmetry imposed on the lagrangian, the FCNC couplings in the quark and lepton sector are fixed in terms of the corresponding mixing matrix (CKM or PMNS), the fermion masses and the ratio $v_2/v_1$ of the vacuum expectation values of the neutral scalars. A large number of processes, including tree and loop level transitions mediated by the new charged or neutral scalars are used as constraints. It i…
Current muon anomalous magnetic moment data have challenged the SM, and seems to open a window to new Physics. Since the difference between SM and experimental predictions is approximately $2.6σ$. In the framework of the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous magnetic moment to get lower and upper bounds for the Flavor Changing Yukawa couplings (FC) in the leptonic sector. We also obtain lower bounds for the mass of the Pseudoscalar Higgs ($m_{A^ 0}$, as a function of the parameters of the model.
In the so called two Higgs doublet model for the top-quark (T2HDM), first suggested by Das and Kao, the top quark receives a special status, which endows it with a naturally large mass, and also potentially gives rise to large flavor changing neutral currents (FCNC) only in the up-quark sector. In this paper we calculate the branching ratio (BR) for the rare decays t->ch and h->tc (h is a neutral Higgs) in the T2HDM, at tree level and at 1-loop when it exceeds the tree-level. We compare our results to predictions from other versions of 2HDM's and find that the scalar FCNC in the T2HDM can play…
We conduct a general discussion of supersymmetric models with three families in the Higgs sector. We analyse the scalar potential, and investigate the minima conditions, deriving the mass matrices for the scalar, pseudoscalar and charged states. Depending on the Yukawa couplings and the Higgs spectrum, the model might allow the occurrence of potentially dangerous flavour changing neutral currents at the tree-level. We compute model-independent contributions for several observables, and as an example we apply this general analysis to a specific model of quark-Higgs interactions, discussing how …
We investigated a general framework of the Standard Model with two Higgs doublets (2HDSM) with suppressed flavor-changing neutral currents (FCNC's). Loop-induced FCNC (and CP-violating) effects, when confronted with experimental constraints for the $K$-$\bar K$, $B$-$\bar B$ and $D$-$\bar D$ mixing and for the $(b \to s γ)$ decay, provide us with constraints on the values of the dominant Yukawa couplings of the charged Higgs, i.e., the values of the couplings of $H^{\pm}$ to $t$ and $b$ quarks. Once these {\it low} energy experimental data relevant for the mixings and for the mentioned decay, …
In the left-right symmetric model based on $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ 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 c…
There is a widespread belief that the general two-Higgs-doublet model (G2HDM) behaves unnaturally with respect to evolution of the flavor-changing neutral Yukawa coupling parameters (FCNYCP's) -- i.e., that the latter, although being suppressed at low energies of probes, in general increase by a large factor as the energy of probes increases. We investigate this, by evolving Yukawa parameters by one-loop renormalization group equations (RGE's) and neglecting contributions of the first quark generation. For patterns of FCNYCP suppression at low energies suggested by the existing quark mass hier…
Higgs boson decays mediated by flavor changing neutral currents (FCNC) are very much suppressed in the Standard Model, at the level of 10^{-15} for Higgs boson masses of a few hundred GeV. Therefore, any experimental vestige of them would immediately call for new physics. In this paper we consider the FCNC decays of Higgs bosons into a top quark in a general two-Higgs-doublet model (2HDM). The isolated top quark signature, unbalanced by any other heavy particle, should help to identify the potential FCNC events much more than any other final state. We compute the maximum branching ratios and t…
The multiple point principle (MPP) can be used to suppress non--diagonal flavour transitions and CP violation in the two Higgs doublet extension of the standard model. We discuss the quasi--fixed point scenario in the MPP inspired two Higgs doublet model which leads to the enhanced production of Higgs particles at the LHC if the MPP scale is low.
The most general two-Higgs doublet model (2HDM) includes potentially large sources of flavor changing neutral currents (FCNCs) that must be suppressed in order to achieve a phenomenologically viable model. The flavor alignment ansatz postulates that all Yukawa coupling matrices are diagonal when expressed in the basis of mass-eigenstate fermion fields, in which case tree-level Higgs mediated FCNCs are eliminated. In this work, we explore models with the flavor alignment condition imposed at a very high energy scale, which results in the generation of Higgs-mediated FCNCs via renormalization gr…
We analyse the constraints and some of the phenomenological implications of a class of two Higgs doublet models where there are flavour-changing neutral currents (FCNC) at tree level but the potentially dangerous FCNC couplings are suppressed by small entries of the CKM matrix $V$. This class of models have the remarkable feature that, as a result of a discrete symmetry of the Lagrangian, the FCNC couplings are entirely fixed in the quark sector by $V$ and the ratio $v_2 /v_1$ of the vevs of the neutral Higgs. The discrete symmetry is extended to the leptonic sector, so that there are FCNC in …
Electroweak baryogenesis in a two-Higgs doublet model is a well-motivated and testable scenario for physics beyond the Standard Model. An attractive way of providing $CP$ violation is through flavor-changing Higgs couplings, where the top-charm coupling is hardly constrained. This minimal scenario can be tested by searching for heavy charged and neutral Higgs bosons at the LHC. While the charged Higgs signature requires a dedicated analysis, the neutral Higgs signature will be covered by a general search for same-sign top pairs. Together, they provide a conclusive test of this kind of baryogen…
We propose a 3+1 Higgs Doublet Model based on the $Δ(27)$ family symmetry supplemented by several auxiliary cyclic symmetries leading to viable Yukawa textures for the Standard Model fermions, consistent with the observed pattern of fermion masses and mixings. The charged fermion mass hierarchy and the quark mixing pattern is generated by the spontaneous breaking of the discrete symmetries due to flavons that act as Froggatt-Nielsen fields. The tiny neutrino masses arise from a radiative seesaw mechanism at one loop level, thanks to a preserved $Z_2^{\left( 1\right)}$ discrete symmetry, which …
We propose an alternative method of constructing two Higgs-doublet models free from scalar mediated FCNC couplings at the tree-level. In a toy scenario, we have presented semi realistic textures for the Yukawa matrices, which can reproduce the approximate flavor structure in the quark sector. Presence of flavor diagonal but nonuniversal Yukawa couplings emerges as a distinguishing feature of such models.
We compare the effectiveness of two hypotheses, Natural Flavour Conservation (NFC) and Minimal Flavour Violation (MFV), in suppressing the strength of flavour-changing neutral-currents (FCNCs) in models with more than one Higgs doublet. We show that the MFV hypothesis, in its general formulation, is more stable in suppressing FCNCs than the hypothesis of NFC alone when quantum corrections are taken into account. The phenomenological implications of the two scenarios are discussed analysing meson-antimeson mixing observables and the rare decays B -> mu+ mu-. We demonstrate that, introducing fla…
Decays of the top quark induced by flavor changing neutral currents (FCNC) are known to be extremely rare events within the Standard Model. This is so not only for the decay modes into gauge bosons, but most notably in the case of the Higgs channels, e.g. t-> H_{SM}+c, with a branching fraction of 10^{-13} at most. Therefore, detection of FCNC top quark decays in a future high-energy, and high-luminosity, machine like the LHC or the LC would be an indisputable signal of new physics. In this paper we show that within the simplest extension of the SM, namely the general two-Higgs-doublet model, …
In this Thesis we have investigated some effects appearing in top quark and Higgs boson decays with flavor changing neutral currents (FCNC) in the framework of generic Two Higgs Doblet Models (2HDM) and the Minimal Supersymmetric Standard Model (MSSM). We have applied these two extensions to the SM to see whether they can produce new FCNC effects. Introductory chapters deal with the 2HDM and the MSSM. In the next chapters we have computed the following FCNC decays: (1) the branching ratios (B) of the top quark to Higgs bosons and charm quark in the 2HDM; (2) B and number of events at the Large…
We present a SUSY model with four Higgs doublets of the ``private type", where each fermion type (up, down, and charged leptons) obtain their masses from a different Higgs doublet H_f ( f = u_1, d, e). The conditions for anomaly cancellation, imply that the remaining Higgs doublet of the model (H_{u_2}), must have the same hypercharge as H_{u_1}, and thus can only couple to up-type quarks, which opens the possibility to have FCNC's only in this sector. We study the Lagrangian of the model, and in particular the Higgs potential, in order to identify the Higgs mass-eigenstates and their interact…
We argue that multiple point principle (MPP) can be used to ensure CP conservation and the absence of flavour changing neutral currents within the two Higgs doublet model (2HDM). We also discuss Higgs phenomenology in the MPP inspired 2HDM.
Recent experimental results on exclusive semi-tauonic B meson decays show sizable deviations from the standard model prediction, while the recent result on pure-tauonic decay reduces the deviation from the prediction. These results suggest an indirect evidence of new physics in which the structure of the relevant weak charged interaction may differ from that of the standard model. We study these tauonic B decays in the context of extensions of the Higgs sector. As a result, we find that two Higgs doublet models without tree-level FCNC are unlikely to explain the present experimental data while…
Consequences of a specific class of two Higgs doublet models in which the Higgs induced tree level flavour changing neutral currents (FCNC) display minimal flavour violation (MFV) are considered. These FCNC are fixed in terms of the CKM matrix elements and the down quark masses. The minimal model in this category with only two Higgs doublets has no extra CP violating phases but such a phase can be induced by adding a complex singlet. Many of the theoretical predictions are similar to other MFV scenario. The FCNC contribute significantly to $B$ meson mixing and CP violation. Detailed numerical …
The meaning of non-abelian super flavorsymmetry in the presence of Multiple Higgs Doublets is twofold: The first one is to order the Yukawa sector of the standard model, while generating the Cheng-Sher suppression of tree-level Flavor Changing Neutral Currents (FCNCs), and the second one is to soften the fine tuning problem in the scalar potential and at the same time to suppress FCNCs coming from the soft breaking of supersymmetry. If spontaneous CP violation is combined with non-abelian super flavorsymmetry the CP phases in the soft supersymmetry breaking sector can disappear. This feature o…
We consider the standard model with two Higgs doublets with the most general Yukawa coupling terms (``type III''). In the model, the neutral-Higgs-mediated flavor-changing neutral currents (FCNC's) are allowed, but must be reasonably suppressed at low energies of probes. It has been known that the existing hierarchies of quark masses render this suppression at low energies rather natural. On the other hand, the model has been regarded by many as unnatural because of the absence of any symmetry that would ensure persistence of this suppression as the energy of probes increases. The opinion has …
We propose a class of Two Higgs Doublet Models where there are Flavour Changing Neutral Currents (FCNC) at tree level, but under control due to the introduction of a discrete symmetry in the full Lagrangian. It is shown that in this class of models, one can have simultaneously FCNC in the up and down sectors, in contrast to the situation encountered in BGL models. The intensity of FCNC is analysed and it is shown that in this class of models one can respect all the strong constraints from experiment without unnatural fine-tuning. It is pointed out that the additional sources of flavour and CP …
The flavor-changing neutral current (FCNC) problem at tree-level is a very critical defect of the two Higgs doublet extension of standard model (SM). In this article, a two-Higgs-doublet model (2HDM) in which such defects do not exist at all is to be demonstrated. The general pattern of matrix pairs which can be diagonalized simultaneously by a same unitary transformation is proposed without extra constraints like symmetries or zeros in M matrices. Only an assumption of the hermiticity of mass matrices is employed in the derivation. With this assumption, number of parameters in the mass matrix…
We show that in a Complementary two-Higgs doublet model(C2HDM) the CP violating phase in the CKM matrix can be generated spontaneously, dangerous FCNC can be naturally suppressed and the strong CP problem can also be avoided. The two Higgs doublets in the model are complementary in the sense that none of them is enough to describe masses of a given type of quarks. We find that the strength of FCNC is suppressed by the strength of Yukawa couplings of the first generation quark and the tree-level FCNC is sufficiently small. Using an explicit example, we show that radiative correction to the assu…
Flavor Changing Neutral Current decays of the top quark within the strict context of the Standard Model are known to be extremely rare. In fact, they are hopelessly undetectable at the Tevatron, LHC and LC in any of their scheduled upgradings. Therefore, if a few of these events eventually show up in the future we will have certainly discovered new physics. We argue that this could well be the case for the LHC and the LC both within the Minimal Supersymmetric Standard Model (MSSM) and in a general two-Higgs-doublet model (2HDM), especially if we look for FCNC top quark decays into Higgs bosons…
The flavor changing neutral current (FCNC) transitions t --> q'H and t --> q'V_i (V_i=γ, g, Z) are studied in the context of the effective Lagrangian approach. We focus on the scenario in which these decays are predominantly induced by new physics effects arising from the Yukawa sector extended with dimension-six SU_L(2) X U_Y(1)-invariant operators, which generate the most general CP-even and CP-odd tq'H vertex at the tree level. For the unknown coefficients, we assume a slightly modified version of the Cheng-Sher ansatz. We found that the branching ratio for the Higgs-mediated FCNC t--> q'V_…
Flavour-Changing-Neutral-Currents (FCNC) play an important r\^ ole in testing the Standard Model (SM) while probing the possibility of having New Physics beyond the SM. In the SM, FCNC are forbidden at three level, but arise through calculable one-loop contributions. We review some of the features of FCNC in two examples of minimal extensions of the SM. In the first example, we consider an extension of the SM consisting of the addition of one vector-like quark either of the up-type ($Q=2/3$) or the down type ($Q=- 1/3$). In this extension there are non-vanishing but naturally suppressed Z-medi…
In this manuscript, a general FCNC-free and CP-violating pattern of quark-mass matrices in the 2HDM derived in our previous investigations is revised. This revised pattern is to be diagonalized analytically with no symmetries imposed. The unitary transformation matrices thus derived depend on only two parameters in each quark type and subsequently lead to a CKM matrix which depends on at most four parameters. The fitting of theoretically derived CKM elements and their corresponding empirical values are as good as ${\bf O}(10^{-2})$ at tree-level. In a phenomenological way which imposes several…
In these proceedings we review the flavour phenomenology of 2HDMs with generic Yukawa structures. We first consider the quark sector and find that despite the stringent constraints from FCNC processes large effects in tauonic B decays are still possible. We then consider lepton flavour observables, show correlations between μ-> eγand μ^- -> e^-e^+e^- in the 2HDM of type III and give upper bounds on the lepton flavour violating B decay B_d -> μe.
Motivated by the fermion mass hierarchy we study the phenomenology of two flavorful two-Higgs-doublet model (2HDM) scenarios. By virtue of the flavor or singular alignment ansatz it is possible to link the mass of a subset of fermions to the vacuum-expectation-value (VEV) of a unique Higgs doublet and to simultaneously avoid flavor-changing-neutral-currents at tree-level. We explicitly construct two models called Type-A and B. There, either the top quark alone or all third generation fermions couple to the doublet with the larger VEV. The other fermions acquire their masses through the small V…
We consider a model for the Higgs sector with two scalar doublets and a broken $Z_2$ symmetry, the Stealth Doublet Model, where the $Z_2$ symmetry is manifest in the Yukawa sector but broken by the scalar potential. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken $Z_2$ symmetry leads to interesting phenomenology such as mixing between the…
The differential branching ratio, CP asymmetry and lepton polarization $P_N$ for $B\to ^M X_sτ^+τ^-$ in a CP spotaneously broken two Higgs doublet model are compute d. ^M It is shown that contributions of neutral Higgs bosons to the decay are ^M quite significant when $\tanβ$ is large and $P_N$ can reach five persent.
We study a simple two Higgs doublet model (2HDM) in the Randall-Sundrum scenario, with an IR brane localized Higgs field and a second doublet arising from a $t\bar{t}$ condensate due to strong Kaluza-Klein gluon effects. The effective 2HDM predicts that the ratio of the brane to condensate vacuum expectation values $\tan β\sim 3$. It also predicts a standard model like Higgs boson of mass ${\mathcal{O}}(100)$ GeV and a heavier scalar at the scale of the lowest KK gluon mass, which we take to be $M_{KK} \gtrsim 1.5$ TeV. The pseudoscalar and the charged scalars are degenerate in mass at tree-le…
We {works done in collaboration with C.S.Kim, Yonsei Univ., Seoul, Korea} present some properties of the SM with two Higgs doublets. Unlike the minimal SM, the Yukawa couplings (in the usual ``type II'' model) converge with the increasing energy to flavor democracy (FD), i.e.~to common values, in a specific flavor basis. This may represent a possible signal of some new, (almost) flavor-blind physics beyond the SM. When imposing the assumption of equality of the corresponding quark and leptonic Yukawa couplings at high transition energies, we can estimate the physical mass of the tau-neutrino a…
The differential branching ratio, forward-backward asymmetry, CP asymmetry and lepton polarization for a B-meson to decay to strange hadronic final states and a $τ^+τ^-$ pair in a CP softly broken two Higgs doublet model are computed. It is shown that contributions of neutral Higgs bosons to the decay are quite significant when $\tanβ$ is large. And it is proposed to measure the direct CP asymmetry in back-forward asymmetry.
We analyze the puzzle of the dimuon CP asymmetry in B_s decays in two Higgs doublet models. We show that the flavor changing neutral current (FCNC) induced by the Higgs coupling in a type III two Higgs doublet model provides a solution to the dimuon charge asymmetry puzzle by enhancing the absorbtive part of the mixing amplitude Γ_{12}^s. We investigate different experimental constraints and show that it is possible to enhance Γ_{12}^s in order to explain the dimuon asymmetry observed by D0. This enhancement requires large Higgs couplings to the first and second generations of quarks which may…
We construct a model where the smallness of the masses of first quark generations implies the near block diagonal nature of the CKM matrix and vice-versa. For this set-up, we rely on a 2HDM structure with an $S_3$ symmetry. We show that an SM-like Higgs emerges naturally from such a construction. Moreover, the ratio of two VEVs, $\tanβ$ can be precisely determined from the requirement of the near masslessness of the up- and down-quarks. The FCNC structure that arises from our model is also very predictive.
We analyzed the S_3 invariant Higgs potential with S_3 singlet and doublet Higgs. We obtained a relation (|v_1|/|v_2|)^2=-sin2phi_2/sin2phi_1 from this S_3 invariant Higgs potential, where v_1, v_2 and phi_1, phi_2 are vacuum pectation values and phases of S_3 doublet Higgs, respectively. This relation could be satisfied exactly by the results |v_1|/ |v_2|=0.207, phi_1=-74.9deg and phi_2=0.74deg obtained from the previous our work analyzing the quark/lepton mass and mixing in S_3 invariant Yukawa interaction. Furthermore, the relation v_S ~ v_D=sqrt{|v_1|^2+|v_2|^2}=174GeV is obtained and then…
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.
We compute all of the one-loop corrections that are enhanced, $O(λ_i λ_j / 16 π^2)$, in the limit $s \gg |λ_i | v^2 \gg M_{W}^2$, $s \gg m_{12}^2$ to all the $2 \to 2$ longitudinal vector boson and Higgs boson scattering amplitudes in the $CP$-conserving two-Higgs doublet model with a softly broken $\mathbb{Z}_2$ symmetry. In the two simplified scenarios we study, the typical bound we find is $|λ_i(s)| \lessapprox 4$.
We argue that the consistent implementation of the multiple point principle (MPP) in the general non-supersymmetric two Higgs doublet model (2HDM) can lead to a set of approximate global custodial symmetries that ensure CP conservation in the Higgs sector and the absence of flavour changing neutral currents (FCNC) in the considered model. In particular the existence of a large set of degenerate vacua at some high energy scale $Λ$ caused by the MPP can result in approximate U(1) and Z(2) symmetries that suppress FCNC and CP--violating interactions in the 2HDM. We explore the renormalisation gro…
There is no tree-level flavor changing neutral current (FCNC) in the standard model (SM) which contains only one Higgs doublet. If more Higgs doublets are introduced for various reasons, the tree level FCNC would be inevitable except extra symmetry was imposed. Therefore FCNC processes are the excellent probes for the physics beyond the SM (BSM). In this paper, we studied the lepton flavor violated (LFV) decay processes $h\rightarrowμτ$ and $τ\rightarrowμγ$ induced by Higgs-$μ$-$τ$ vertex. For $τ\rightarrowμγ$, its branching ratio is also related to the $ht\bar{t}$, $hτ^+τ^-$ and $hW^+W^-$ ver…
We study the differential branching ratio, forward-backward asymmetry, CP-violating asymmetry, CP-violating asymmetry in the forward-backward asymmetry and polarization asymmetries of the final lepton in the B-> X_d \ell^+\ell^- decays in the context of a CP softly broken two Higgs doublet model. We analyze the dependencies of these observables on the model parameters by paying a special attention to the effects of neutral Higgs boson (NHB) exchanges and possible CP violating effects. We find that NHB effects are quite significant for the τmode. The above-mentioned observables seems to be prom…
A class of non-supersymmetric extensions of the Standard Model is proposed in which there is a multiplicity of light scalar doublets in a multiplet of a non-abelian family group with the Standard Model Higgs doublet. Anthropic tuning makes the latter light, and consequently the other scalar doublets remain light because of the family symmetry. The family symmetry greatly constrains the pattern of FCNC and proton decay operators coming from scalar-exchange. Such models show that useful constraints on model-building can come from an extended naturalness principle when the electroweak scale is an…
The top quark flavor changing neutral current (FCNC) process is an excellent probe to search for new physics in top sector since the Standard Model expectation is extremely suppressed. We explore Higgs-mediated top quark FCNC, focusing on $H$-$t$-$c$ Yukawa coupling $λ_{ct}$ within the general two Higgs doublet model. After electroweak symmetry breaking the top quark FCNC couplings are included in the charged Higgs Yukawa sector so that they contribute to various processes in flavor physics. To probe $λ_{ct}$, we study anomalous single top production and the same sign top pair production at th…
Quark models with four-fermion interaction including derivatives of fields in the strong coupling regime are used to implement composite-Higgs extensions of the Standard Model. In this approach the dynamical breaking of chiral symmetry occurs in two (or more) channels (near polycritical values for coupling constants), giving rise to two (or more) composite Higgs doublets. Two types of models are built for which Flavour Changing Neutral Currents (FCNC) are naturally suppressed. In the first Model I the second Higgs doublet is regarded as a radial excitation of the first one. In the second Model…
We study the differential branching ratio, forward-backward asymmetry, CP-violating asymmetry, CP-violating asymmetry in the forward-backward asymmetry and polarization asymmetries in the $B -> K \ell^+ \ell^-$ and $B -> K^* \ell^+ \ell^-$ decays in the context of a CP softly broken two Higgs doublet model. We analyze the dependencies of these observables on the model parameters by paying a special attention to the effects of neutral Higgs boson (NHB) exchanges and possible CP violating effects. We find that NHB effects are quite significant for both decays. A combined analysis of above-mentio…
A two Higgs doublet model (2HDM) is one of the minimal extensions of the Standard Model (SM), and it is well-known that the general setup predicts the flavor-violating phenomena, mediated by neutral Higgs interactions. Recently the CMS collaboration has reported an excess of the lepton-flavor-violating Higgs decay in $h \rightarrow μτ$ channel with a significance of 2.5 $ σ$. We investigate the CMS excess in a general 2HDM with tree-level Flavor Changing Neutral Currents (FCNCs), and discuss its impact on the other physical observations. Especially, we see that the FCNCs relevant to the excess…
Based on current data of the Higgs boson search at the Large Hadron Collider, we constrain the parameter space of the two-Higgs doublet models where a softly broken $Z_2$ symmetry is employed to avoid flavor-changing neutral currents at tree level. There are four types of Yukawa interactions under the $Z_2$ charge assignments of the standard model fermions. We find that the model with type-II Yukawa interactions can better explain the experimental data among all. In this scenario, the couplings of the light CP-even Higgs boson $h$ with weak gauge bosons are almost standard model-like or only s…
We consider recent LHC flavour and Higgs results to constraint a custodial vectophobic Two-Higgs-Doublet-Model (2HDM) where the Minimal Flavour Violation principle (MFV) is implemented to suppress (pseudo)scalar induced flavour changing neutral currents (FCNC).
I present a model with two scalar doublets and a softly broken $\ztwo$ symmetry, where only one of the doublets gets a vacuum expectation value and couples to fermions at tree-level. The softly broken $\ztwo$ symmetry leads to interesting phenomenology such as mixing between the two doublets and a charged scalar H^\pm which can be light and dominantly decays into W γ. The model can also naturally reproduce an enhanced γγsignal of the newly observed Higgs boson at the LHC with mass 125 GeV.
A non-Abelian flavour symmetry in a minimal supersymmetric standard model can explain the flavour structures in the Yukawa couplings and simultaneously solve the SUSY flavour problem. Similarly the SUSY CP problem can be solved if CP is spontaneously broken in the flavour sector. In this work, we present an explicit example of these statements with a SU(3) flavour symmetry and spontaneous CP violation. In addition, we show that it is still possible to find some significant deviation from the SM expectations as far as FCNC and CP violation are concerned. We find that large contributions can be …
We propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)_H gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)_H charges. Then one can easily avoid the tree level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z_2 symmetry, and the pseudoscalar boson could be eaten by extra Z_H boson. Imposing the anomaly cancellation, we find that the U(1)_H in the Type-II and Type-IV 2HDM's become leptophobic and leptophilic, respectively. For the Type-I case, U(1)_H…
