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Register a new userHiggs--Flavon Mixing and $h rightarrow mutau$
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ATLAS and CMS have reported an excess in the flavor violating decay of the Higgs boson, $h rightarrow mu tau$. We show that this result can be accommodated through a mixing of the Higgs with a flavon, the field responsible for generating the Yukawa matrices in the lepton sector. We employ a version of the Froggatt-Nielsen mechanism at the electroweak scale, with only the leptons and the flavon transforming non--trivially under the corresponding symmetry group. Non--observation of charged lepton flavor violation (LFV) in other processes imposes important constraints on the model, which we find to be satisfied in substantial regions of parameter space.
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We consider a composite Higgs model based on the $SU(6)/Sp(6)$ coset, where an $U(1)$ subgroup of $Sp(6)$ is identified as the flavor symmetry. A complex scalar field $s$, which is a pseudo-Nambu-Goldstone boson of the broken symmetry, carries a flavor charge and plays the role of a flavon field. The $U(1)_F$ flavor symmetry is then broken by a VEV of the flavon field, which leads to a small parameter and generates the mass hierarchy between the top and bottom quarks. A light flavon below the TeV scale can be naturally introduced, which provides a fully testable model for the origin of flavor hierarchy. A light flavon also leads to substantial flavor changing neutral currents, which are strongly constrained by the flavor precision tests. The direct search of additional scalar bosons can also be conducted in HL-LHC and future hadron colliders.
We construct a supersymmetric $S_4$ flavor symmetry model with one of the trimaximal neutrino mixing patterns, the so-called TM$_1$, by using the novel way to stabilize flavons, which we proposed recently. The flavons are assumed to have tachyonic supersymmetry breaking mass terms and stabilized by higher-dimensional terms in the potential. We can obtain the desired alignment structure of the flavon vacuum expectation values to realize neutrino masses and mixings consistent with the current observations. This mechanism naturally avoids the appearance of dangerous cosmological domain walls.
We consider lepton flavor violating Higgs decay, specifically $h to mutau$, in a leptoquark model. We introduce two scalar leptoquarks with the $SU(3)_c times SU(2)_L times U(1)_Y$ quantum numbers, $(3,2,7/6)$ and $(3,2,1/6)$, which do not generate the proton decay within renormalizable level. They can mix with each other by interactions with the standard model Higgs. The constraint from the charged lepton flavor violating process, $tau^{-} to mu^{-} gamma$, is very strong when only one leptoquark contribution is considered. However, we demonstrate that significant cancellation is possible between the two leptoquark contributions. We show that we can explain the CMS (ATLAS) excess in $h to mu tau$. We also show that muon $(g-2)$ anomaly can also be accommodated.
The significance of new physics appearing in the loop-induced decays of neutral Higgs bosons into pairs of dibosons $gammagamma$ and $Zgamma$ will be discussed in the framework of the 3-3-1 models based on a recent work~cite{Okada:2016whh}, where the Higgs sector becomes effectively the same as that in the two Higgs doublet models (2HDM) after the first symmetry breaking from $SU(3)_L$ scale into the electroweak scale. For large $SU(3)_L$ scale $v_3simeq10$ TeV, dominant one-loop contributions to the two decay amplitudes arise from only the single charged Higgs boson predicted by the 2HDM, leading to that experimental constraint on the signal strength $mu^{331}_{gammagamma}$ of the Standard Model-like Higgs boson decay $hrightarrow gammagamma$ will result in a strict upper bound on the signal strength $mu^{331}_{Zgamma}$ of the decay $hrightarrow, Zgamma$. For a particular model with lower $v_3$ around 3 TeV, contributions from heavy charged gauge and Higgs bosons may have the same order, therefore may give strong destructive or constructive correlations. As a by-product, a deviation from the SM prediction $|mu^{331}_{gammagamma}-1| le 0.04$ still allows $|mu^{331}_{Zgamma}-1|$ to reach values near 0.1. We also show that there exists an $CP$-even neutral Higgs boson $h^0_3$ predicted by the 3-3-1 models, but beyond the 2HDM, has an interesting property that the branching ratio Br$(h^0_3rightarrow gammagamma)$ is very sensitive to the parameter $beta$ used to distinguish different 3-3-1 models.
We report consistent results for $Gamma(h rightarrow gamma gamma)$, $sigma(mathcal{G} ,mathcal{G}rightarrow h)$ and $Gamma(h rightarrow mathcal{G} ,mathcal{G})$ in the Standard Model Effective Field Theory (SMEFT) perturbing the SM by corrections $mathcal{O}(bar{v}_T^2/16 pi^2 Lambda^2)$ in the Background Field Method (BFM) approach to gauge fixing, and to $mathcal{O}(bar{v}_T^4/Lambda^4)$ using the geometric formulation of the SMEFT. We combine and modify recent results in the literature into a complete set of consistent results, uniforming conventions, and simultaneously complete the one loop results for these processes in the BFM. We emphasise calculational scheme dependence present across these processes, and how the operator and loop expansions are not independent beyond leading order. We illustrate several cross checks of consistency in the results.
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