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Register a new user$htomutau$ and muon g-2 in the alignment limit of two-Higgs-doublet model
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We examine the $hto mutau$ 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 $hmutau$ is absent. We assume the lepton-flavor-violating $mutau$ 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 electroweak data, $B$-meson decays, $tau$ decays and Higgs searches, we find that the muon g-2 anomaly and $mutau$ excess favor the small lepton Yukawa coupling and top Yukawa coupling of the non-SM-like Higgs around 125 GeV, and the lepton-flavor-violating coupling is sensitive to another heavy neutral Higgs mass. In addition, if the $mutau$ excess is from $H$ around 125 GeV, the experimental data of the heavy Higgs decaying into $mutau$ favor $m_A>230$ GeV for a relatively large $Hbar{t}t$ coupling.
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In this paper we simultaneously explain the excesses of the 750 GeV diphoton, muon g-2 and $hto mutau$ 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 $tautomugamma$, muon g-2 and the 750 GeV diphoton data. We scan over the parameter space and find that such an extension can simultaneously account for the observed excesses of 750 GeV diphoton, muon g-2 and $hto mutau$. The 750 GeV resonance decays in exotic modes, such as $Pto hA$, $Pto HZ$, $Pto HA$ and $Pto W^pm H^mp$, and its width can be dozens of GeV and is sensitive to the mixing angle.
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 $lesssim m_H^{} lesssim 50$ GeV, or $ 10$ GeV $lesssim m_A^{} lesssim 130$ GeV, with enhanced couplings to tau leptons. The charged Higgs boson is typically heavier, with $200$ GeV $ lesssim m^{}_{H^+} lesssim 630$ GeV. The surviving parameter space is forced into the CP-conserving limit by EDM constraints. Some Standard Model observables may be significantly modified, including a possible new decay mode of the SM-like Higgs boson to four taus. We comment on future measurements and direct searches for those effects at the LHC as tests of the model.
Recent progress on muon $g-2$ measurement prompts one to take it even more seriously. In the general two Higgs doublet model that allows extra Yukawa couplings, we take a simplified approach of single enhanced coupling. We fix the charged lepton flavor violating coupling, $rho_{taumu} = rho_{mutau}$, via the one-loop mechanism, for illustrative masses of the heavy scalar $H$ and pseudoscalar $A$, where we assume $m_A = m_{H^+}$. Since extra top Yukawa couplings are plausibly the largest, we turn on $rho_{tt}$ and find that LHC search for $gg to H,,A to taumu$ gives more stringent bound than from $tauto mugamma$ with two-loop mechanism. Turning on a second extra top Yukawa coupling, $rho_{tc}$, can loosen the bound on $rho_{tt}$, but LHC constraints can again be more stringent than from $B to Dmu u$ vs $De u$ universality. This means that evidence for $H,,A to taumu$ may yet emerge with full LHC Run 2 data, while direct search for $tau^pmmu^mp bW^+$ or $tbar cbW^+$ (plus conjugate) may also bear fruit.
The recent Fermilab measurement of the muon anomalous magnetic moment yields $4.2 sigma$ deviation from the SM prediction, when combined with the BNL E821 experiment results. In the Type-X two Higgs doublet model with the Higgs alignment, we study the consequence of imposing the observed muon $g-2$, along with theoretical stabilities, electroweak oblique parameters, Higgs precision data, and direct searches. For a comprehensive study, we scan the whole parameter space in two scenarios, the normal scenario where $h_{rm SM} = h$ and the inverted scenario where $h_{rm SM}=H$, where $h$ ($H$) is the light (heavy) CP-even Higgs boson. It is found that large $tanbeta$ ($gtrsim 100$) and light pseudoscalar mass $M_A$ are required to explain the muon $g-2$ anomaly. This, in turns, implies that it is difficult to maintain the theoretical stability unless the scalar masses satisfy $M_A^2 simeq M_{H^pm}^2 simeq m_{12}^2 tanbeta approx M_{H/h}^2$. The direct search bounds at the LEP and LHC exclude the small $M_A$ window below $m_{h_{rm SM}}/2$. We also show that the observed electron anomalous magnetic moment is consistent with the model prediction but the lepton flavor universality data in the $tau$ and $Z$ decays are not. For a separate exploration of the model, we propose the golden mode $pp to A h/AH to 4 tau$ at the HL-LHC, which has a high potential to probe the whole surviving parameter space.
We show that one of the simplest extensions of the Standard Model, the addition of a second Higgs doublet, when combined with a dark sector singlet scalar, allows us to: $i)$ explain the long-standing anomalies in the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE (MB) while maintaining compatibility with the null result from KARMEN, $ii)$ obtain, in the process, a portal to the dark sector, and $iii)$ comfortably account for the observed value of the muon $g-2$. Three singlet neutrinos allow for an understanding of observed neutrino mass-squared differences via a Type I seesaw, with two of the lighter states participating in the interaction in both LSND and MB. We obtain very good fits to energy and angular distributions in both experiments. We explain features of the solution presented here and discuss the constraints that our model must satisfy. We also mention prospects for future tests of its particle content.
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