Recently, Kajiyama, Okada and Yagyu (KOY) proposed an electron/muon specific two Higgs doublet model. In this model, an S3 symmetry suppresses flavor changing neutral currents instead of a Z2 symmetry. In the "Type I" version of the model, the heavy Higgs bosons have a greatly enhanced coupling to electrons and muons. KOY studied the phenomenology of the heavy Higgs bosons at the LHC. In this paper, the phenomenology at electron-positron colliders is studied. For the heavy Higgs mass range between 150 and 210 GeV, bounds from LEP-200 are stronger than those from the LHC. The model allows for the interesting possibility that muon pair production at the ILC can be mediated by s-channel Higgs exchange. This requires an energy scan. The scanning rate and necessary resolution are discussed.
We investigate the iso-doublet vector leptoquark $V_2$ as a solution to the $B$ anomalies $R_{K, K^*}$ and $R_{D,D^*}$, as well as explaining the muon and electron anomalous magnetic moments, and the very recent $W$-mass anomaly.
We calculate the new physics effects on the anomalous magnetic moment of the muon in the framework of the two Higgs doublet model. We predict an upper bound for the lepton flavor violating coupling, which is responsible for the point like interaction between muon and tau, by using the uncertainty in the experimental result of the muon anomalous magnetic moment. We show that the upper bound predicted is more stringent compared to the one which is obtained by using the experimental result of the muon electric dipole moment
Pseudoscalar and charged Higgs bosons production in the processes $μ^+ μ^-\to P^0_i Z^0$, $μ^+μ^- \to H^{\pm}W^{\mp}$ within the models with several Higgs doublets and singlets is considered.
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).
We investigate a new type of a two-Higgs-doublet model as a solution of the muon $g-2$ anomaly. We impose a softly-broken $Z_4$ symmetry to forbid tree level flavor changing neutral currents in a natural way. This $Z_4$ symmetry restricts the structure of Yukawa couplings. As a result, extra Higgs boson couplings to muons are enhanced by a factor of $\tanβ$, while their couplings to all the other standard model fermions are suppressed by $\cotβ$. Thanks to this coupling property, we can avoid the constraint from leptonic $τ$ decays in contrast to the lepton specific two-Higgs-doublet model, wh…
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.
We investigate a two Higgs doublet model with extra flavour depending $U(1)_X$ gauge symmetry where $Z'$ boson interactions can explain the Atomki anomaly by choosing appropriate charge assignment for the SM fermions. For parameter region explaining the Atomki anomaly we obtain light scalar boson with $\mathcal{O}(10)$ GeV mass, and we explore scalar sector to search for allowed parameter space. We then discuss anomalous magnetic dipole moment of muon and lepton flavour violating processes induced by Yukawa couplings of our model.
We describe a class of models of electroweak symmetry breaking that involves strong dynamics and top quark condensation. A new scheme based upon a seesaw mechanism appears particularly promising. Various implications for the first-stage muon collider are discussed.
We propose a two-Higgs-doublet model in which one Higgs doublet has the same interactions with fermions as the SM, and another Higgs doublet only has the $μ$-$τ$ LFV interactions. Assuming that the Yukawa matrices are real and symmetric, we impose various relevant theoretical and experimental constraints, and find that the excesses of muon $g-2$ and lepton flavour universality in the $τ$ decays can be simultaneously explained in the region of small mass splittings between the heavy CP-even Higgs and the CP-odd Higgs ($m_A > m_H$). The multi-lepton event searches at the LHC can sizably reduce t…
We consider two possible sources of the $T$-violating muon transverse polarization in the process $K^+ \to μ^+ νγ$: electromagnetic final state interaction in the SM and contribution due to charged-Higgs exchange diagrams in the framework of the Weinberg three doublets model. It is shown that at the one-loop level of the SM the muon transverse polarization, $P_T^{SM}$, varies within $(0.0 ÷1.1 \cdot 10^{-3})$ in the Dalitz plot region. Averaged value of the muon polarization, $<P^{SM}_T>$, in the kinematic region of $E_γ\geq 20$ MeV is equal to $4.76\cdot 10^{-4}$. In the case of the model wit…
Current experimental data from the $g-2$ muon factor, seems to show the necessity of physics beyond the Standard Model (SM), since the difference between SM and experimental predictions is 2.6$σ$. 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 Flavour Changing (FC) Yukawa couplings 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.
The historic LHC discovery of the 125 GeV particle with properties that closely resemble the Standard Model (SM) Higgs boson verifies our understanding of electroweak symmetry breaking, but solidifies the need for a resolution to the hierarchy problem. Many extensions of the SM that address the hierarchy problem contain a non-minimal Higgs sector. Therefore, as a benchmark alternative to the SM Higgs mechanism, we study a general 2 Higgs doublet model (2HDM-G) framework for evaluating future sensitivity to Higgs couplings. We study how well it can be distinguished from the SM Higgs boson by fu…
Updating various theoretical and experimental constraints on the four different types of two-Higgs-doublet models (2HDMs), we find that only the ``lepton-specific" (or ``type X") 2HDM can explain the present muon g$-$2 anomaly in the parameter region of large $\tanβ$, a light CP-odd boson, and heavier CP-even and charged bosons which are almost degenerate. The severe constraints on the models come mainly from the consideration of vacuum stability and perturbativity, the electroweak precision data, the $b$-quark observables like $B_S \to μμ$, the precision measurements of the lepton universalit…
The manner in which the parameters of a two-Higgs-doublet model can be chosen so that no Higgs boson is discovered at a $\sqrt{s}\leq 800\gev$ $\epem$ collider, while maintaining consistency with current precision electroweak measurements, is described. The importance of a Giga-$Z$ factory and higher collider energies for such a scenario is emphasized.
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…
We discuss the status of the Inert Doublet Model, a two-Higgs doublet model that obeys a discrete Z2 symmetry and provides a dark matter candidate. We discuss all current theoretical and experimental constraints on the model as well as discovery prospects at current and future colliders.
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…
We examine the possibilities of accommodating the muon $g-2$ anomaly reported by Fermilab in the 2HDM with a discrete $Z_4$ symmetry in which an inert Higgs doublet field ($H,~A,~H^\pm$) has the lepton flavor violation $μ$-$τ$ interactions. We study the case of light $H$ (5 GeV $<m_H<$ 115 GeV) and assume the Yukawa matrices to be real and symmetrical. Considering relevant theoretical and experimental constraints, especially for the multi-lepton searches at the LHC, we find the muon $g-2$ anomaly can be explained within $2σ$ range in the region of 5 GeV $<m_H<20$ GeV, 130 GeV $< m_A~(m_{H^\pm}…
We present an extension of the GM2Calc software to calculate the muon anomalous magnetic moment ($a_μ^{\text{BSM}}$) in the Two-Higgs Doublet Model. The Two-Higgs Doublet Model is one of the simplest and most popular extensions of the Standard Model. It is one of the few single field extensions that can give large contributions to $a_μ^{\text{BSM}}$. It is essential to include two-loop corrections to explain the long standing discrepancy between the Standard Model prediction and the experimental measurement in the Two-Higgs Doublet Model. The new version GM2Calc 2 implements the state of the a…
Muon colliders might greatly extend the energy frontier of collider physics. One can contemplate circular colliders with center-of-mass energies in excess of 10 TeV. Some physics issues that might be relevant at such a machine are discussed.
We present benchmarks for the Inert Doublet Model, a Two Higgs Doublet Model with a dark matter candidate. They are consistent with current constraints on direct detection, including the most recent bounds from the XENON1T experiment and relic density of dark matter, as well as with known collider and low-energy limits. We focus on parameter choices that promise detectable signals at lepton colliders via pair-production of H+H- and HA. For these we choose a large variety of benchmark points with different kinematic features, leading to distinctly different final states in order to cover the la…
Combining the multi-lepton searches at the LHC, we study the possibilities of accommodating the new data of muon and electron $g-2$ anomalies in the lepton-specific inert two-Higgs-doublet model. We take the heavy CP-even Higgs as the 125 GeV Higgs, and find the muon and electron $g-2$ anomalies can be explained simultaneously in the region of 5 GeV $< m_h<60$ GeV, 200 GeV $<m_A< 620$ GeV, 190 GeV $<m_{H^\pm}< 620$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. Meanwhile, the model can give a better fit to the data of lepton universality in $τ$ decays than the SM. Furthe…
In this paper we simultaneously explain the excesses of the 750 GeV diphoton, muon g-2 and $h\to μτ$ in an extension of the two-Higgs-doublet model (2HDM) with additional vector-like fermions and a CP-odd scalar singlet ($P$) which is identified as the 750 GeV resonance. This 750 GeV resonance has a mixing with the CP-odd scalar ($A$) in 2HDM, which leads to a coupling between $P$ and the SM particles as well as a coupling between $A$ and the vector-like fermions. Such a mixing and couplings are strongly constrained by $τ\toμγ$, muon g-2 and the 750 GeV diphoton data. We scan over the paramete…
The muon anomalous magnetic moment is investigated in the standard model with two Higgs doublets (S2HDM) motivated from spontaneous CP violation. Thus all the effective Yukawa couplings become complex. As a consequence of the non-zero phase in the couplings, the one loop contribution from the neutral scalar bosons could be positive and negative relying on the CP phases. The interference between one and two loop diagrams can be constructive in a large parameter space of CP-phases. This will result in a significant contribution to muon anomalous magnetic moment even in the flavor conserving proc…
The CP violating two-Higgs doublet model of type-X may enhance significantly the electric and magnetic moment of leptons through two-loop Barr-Zee diagrams. We analyze the general parameter space of the type-X 2HDM consistent with the muon $g-2$ and the electron EDM measurements to show how strongly the CP violating parameter is constrained in the region explaining the muon $ g-2$ anomaly.
High luminosity muon-muon colliders would provide a powerful new probe of Higgs boson physics through $s$-channel resonance production. We discuss the prospects for detection of Higgs bosons and precision measurements of their masses and widths at such a machine.
Signatures for sleptons, which have been extensively studied for the Next Linear Collider, are reexamined taking into account some of the different features of a First Muon Collider.
The muon-proton ($μp$) collider is an interesting option of the muon collider. Here we discuss the physics potential of the $μp$ collider; especially, leptoquarks and contact interactions. We calculate the sensitivity reach for the second generation leptoquarks and leptogluons, $R$-parity violating squarks, and $μq$ contact interactions for the $μp$ colliders of various energies and luminosities.
A scenario augmenting the well known Type-X Two-Higgs doublet model (2HDM) with an additional inert doublet is proposed. The Type-X 2HDM is known to offer a solution to the muon $g-2$ anomaly for a light pseudoscalar. We show that the proposed framework can accomodate a heavier pseudoscalar on account of two-loop Barr-Zee (BZ) contributions to muon $g-2$ stemming from the inert doublet. We subsequently explore an interesting $τ^+τ^- + $ missing transverse energy signal that can be used to probe the present scenario at the 14 TeV LHC.
We propose a model for the vector-like lepton to explain the small muon mass by a seesaw mechanism, based on lepton-specific two Higgs doublet models with a local $U(1)'$ symmetry. There is no bare muon mass for a nonzero $U(1)'$ charge of the leptophilic Higgs doublet, so the physical muon mass is generated due to the mixing between the vector-like lepton and the muon after the leptophilic Higgs doublet and the dark Higgs get VEVs. In this scenario, the non-decoupling effects of the vector-like lepton give rise to leading contributions to the muon $g-2$, thanks to the light $Z'$ and the light…
Data from the Muon g-2 experiment and measurements of the fine structure constant suggest that the anomalous magnetic moments of the muon and electron are at odds with standard model expectations. We survey the ability of axion-like-particles, two-Higgs-doublet models and leptoquarks to explain the discrepancies. We find that accounting for other constraints, all scenarios except the Type-I, Type-II and Type-Y two-Higgs-doublet models fit the data well.
If the Standard Model of particle interactions is extended to include a second scalar doublet $[H^{+},(H^{0}+iA^{0})/\sqrt{2}]$, which is odd under an unbroken Z_{2} discrete symmetry, it may be called the $dark$ scalar doublet, because its lightest neutral member, say H^{0}, is one posssible component for the dark matter of the Universe. We discuss the general phenomenology of the four particles of this doublet, without assuming that H^{0} is the dominant source of dark matter. We also consider the impact of this $dark$ scalar doublet on the phenomenology of the SM Higgs boson h.
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 discuss the model independent parameterization for a strongly interacting electroweak sector. Phenomenological studies are made to probe such a sector for future colliders such as the LHC, $e^+e^-$ Linear collider and a muon collider.
We study the high-scale validity of a Type-X two Higgs doublet scenario which provides an explanation of the observed value of muon $(g-2)$. This region admits of a pseudoscalar physical state, which is well below the observed 125-GeV scalar in mass. A second neutral scalar particle can be both above and below 125 GeV in such a scenario. Admissible regions in the parameter space are obtained by using the most recent data on muon $(g-2)$, theoretical constraints such as low-scale perturbativity and vacuum stability, and also all experimental constraints, including the available LHC results. Amo…
We analyze allowed region of muon anomalous magnetic moment (muon $g-2$), satisfying lepton flavor violations, $Z$ boson decays, and collider physics, in a framework of multi-charged particles. Then we explore the typical size of the muon $g-2$, and discuss which modes dominantly affect muon $g-2$.
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 …
One of the main motivations to look beyond the SM is the discrepancy between the theoretical prediction and observation of anomalous magnetic moment of muon. Alleviating this tension between theory and experiment and satisfying the bounds from lepton flavor violation data simultaneously is a challenging task. In this paper, we consider generalised Two Higgs Doublet Model, with a Yukawa structure as a perturbation of Type X Two Higgs Doublet Model. In view of this model, we explore muon anomaly and lepton flavor violation along with constraints coming from B-physics, theoretical constraints, el…
We calculate contributions to the anomalous magnetic moment of the muon from heavy neutral and charged Higgs bosons and new leptons in two Higgs doublet models extended by vectorlike leptons. We present detailed predictions of two models with type-II couplings to standard model fermions, motivated by a $Z_2$ symmetry and supersymmetry. In addition, we compare the results with the standard model extended by vectorlike leptons. We find that the model motivated by a $Z_{2}$ symmetry can generate much larger contributions to the magnetic moment compared to the standard model, even by two orders of…
We calculate the cross section of the lightest Higgs boson pair production at the Photon Linear Collider in the two Higgs doublet model. We focus on the scenario in which the lightest Higgs boson has the standard model like couplings to gauge bosons. We take into account the one-loop correction to the $hhh$ coupling as well as additional one-loop diagrams due to charged bosons to the $γγ\to hh$ helicity amplitudes. We discuss the impact of these corrections on the $hhh$ coupling measurement at the Photon Linear Collider.
In this note, we show how one can attribute the anomaly currently present in the measurement of the anomalous magnetic moment of the muon ($a_μ$) to the presence of an underlying Aligned 2-Higgs Doublet Model (A2HDM) with Right-Handed (RH) neutrinos, $ν_R$. The effects of the latter scenario are driven by one and two-loop topologies wherein a very light CP-odd neutral Higgs state ($A$) contributes significantly to $a_μ$. Over the region of parameter space of our new physics model which explains the aforementioned anomaly, also consistent with the most recent measurements of the electron anomal…
In this work, we introduce an extra singlet pseudoscalar into the Type-III two Higgs doublet model (2HDM) which is supposed to solve a series of problems in the modern particle-cosmology. With existence of a light pseudoscalar, the $h\rightarrowμτ$ excess measured at CMS and as well as the $(g-2)_μ$ anomaly could be simultaneously explained within certain parameter spaces that can also tolerate the data on the flavor-violating processes $τ\rightarrowμγ$ and Higgs decay gained at LHC. Within the same parameter spaces, the DM relic abundance is well accounted. Moreover, the recently observed Gal…
The two Higgs doublet model (THDM) is a simple extension of the standard model, which can provide a low energy effective description of more fundamental theories. The model contains additional Higgs bosons, and predicts rich phenomenology especially due to the variation of Yukawa interactions. Under imposing a softly broken discrete symmetry, there are four independent types of Yukawa interactions in THDMs. In this review, we briefly summarize bounds from current experimental data on THDMs and implications at future collider experiments. We pay special attention to the collider phenomenology o…
We study the discovery potential for heavy axion-like particles (ALPs) and the perspectives for determining their coupling properties at a muon collider. Focusing on their couplings to the Standard Model (SM) gauge bosons $γ, Z, W^\pm$, we show that a high-energy muon collider can substantially extend the mass coverage, essentially reaching the kinematic limit of the collider energy. The unique kinematics allow for non-ambiguous determination of the individual coupling strengths. The associated production via $μ^+μ^-$ annihilation and the VBF processes with the tagged outgoing muons can be uti…
This contribution describes precision width measurements that could be done at a muon collider for very narrow resonances as the Higgs or a possible pseudogoldstone boson, or for almost degenerate resonances as the A0 and H0 in the MSSM for large values of tanβ.
Muon colliders are expected to naturally have a small spread in beam energy making them an ideal place to study the excitation curve. We present the parameter determinations that are possible from measuring the total cross section near threshold at a $μ^+μ^-$ collider.
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 $\lesssim m_H^{} \lesssim 50$ G…
We propose a minimal model which accommodates the long-standing anomaly of muon magnetic moment based on abelian discrete flavor symmetries. The standard model is extended by scalar doublets charged under a $Z_n$ lepton flavor symmetry. In these models, a large contribution to the muon magnetic moment can be obtained by the chirality enhancement from new scalar mediated diagrams without conflicting with the flavor symmetry. Thanks to the lepton flavor symmetry, these models automatically forbid lepton flavor violation. The minimal model is based on $Z_4$ symmetry with only one extra scalar dou…
The charged Higgs associated production with a W boson has a smooth cross section as a function of the charged Higgs mass at muon colliders. The cross section in Minimal Supersymmetric Standard Model is about 25fb in the range 200 GeV < mH < 400 GeV with tanbeta = 50. This is much larger than the corresponding cross section at an e+e- collider which reaches a fraction of femtobarn. The observability of this channel at a muon collider has been recently studied in an earlier work leading to the result that with 1 ab-1, a 5sigma signal can be observed throughout the aforementioned mass range. In …
Conceptual design studies are underway for muon colliders and other high-current muon storage rings that have the potential to become the first true ``neutrino factories''. Muon decays in long straight sections of the storage rings would produce precisely characterized beams of electron and muon type neutrinos of unprecedented intensity. This article reviews the prospects for these facilities to greatly extend our capabilities for neutrino experiments, largely emphasizing the physics of neutrino interactions.
We examine the one loop contributions arising in the Two-Higgs-Doublet Model (THDM) to the W-boson anomalous magnetic dipole and electric quadrupole form factors for both photon and Z couplings relevant at collider energies. While the model parameter and $q^2$-dependencies of these form factors are found to be significant, the corresponding size of these corrections are relatively small in comparison to unity. They are, however, found to be comparable in magnitude to the usual Standard Model loop corrections. Radiative corrections to the Higgs particle masses and couplings due to heavy top-qua…
We have investigated the production potential of the spin-1/2 excited muons, predicted by the preonic models, at the four SPPC (Super Proton-Proton Collider)-based muon-proton colliders in different center-of-mass energies. For the signal process μp\rightarrowμ^{\star}X\rightarrowμγX, the production cross-section and the decay width values of the excited muons have been calculated. The pseudorapidity and transverse momentum distributions of the final state particles of muons and photons have been obtained to be determine the kinematical cuts best suited for discovery of the excited muons. By a…
We examine the $h\to μτ$ and muon g-2 in the exact alignment limit of two-Higgs-doublet model. In this case, the couplings of the SM-like Higgs to the SM particles are the same as the Higgs couplings in the SM at the tree level, and the tree-level lepton-flavor-violating coupling $hμτ$ is absent. We assume the lepton-flavor-violating $μτ$ excess observed by CMS to be respectively from the other neutral Higgses, $H$ and $A$, which almost degenerates with the SM-like Higgs at the 125 GeV. After imposing the relevant theoretical constraints and experimental constraints from the precision electrow…
