H. L. T. Mai | Searcharxiv

arXiv2023

One-loop contributions to decays $e_b\to e_a γ$ and $(g-2)_{e_a}$ anomalies, and Ward identity

In this paper, we will present analytic formulas to express one-loop contributions to lepton flavor violating decays $e_b\to e_a γ$, which are also relevant to the anomalous dipole magnetic moments of charged leptons $e_a$. These formulas were computed in the unitary gauge, using the well-known Passarino-Veltman notations. We also show that our results are consistent with those calculated previously in the 't Hooft-Veltman gauge, or in the limit of zero lepton masses. At the one-loop level, we show that the appearance of fermion-scalar-vector type diagrams in the unitary gauge will violate the Ward Identity relating to an external photon. As a result, the validation of the Ward Identity guarantees that the photon always couples with two identical particles in an arbitrary triple coupling vertex containing a photon.

hep-ph↗

arXiv2019

Neutral Higgs decays $H \rightarrow Z γ,γγ$ in 3-3-1 models

The significance of new physics appearing in the loop-induced decays of neutral Higgs bosons into pairs of dibosons $γγ$ and $Zγ$ 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 $v_3\simeq10$ 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 $μ^{331}_{γγ}$ of the Standard Model-like Higgs boson decay $h\rightarrow γγ$ will result in a strict upper bound on the signal strength $μ^{331}_{Zγ}$ of the decay $h\rightarrow\, Zγ$. 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 $|μ^{331}_{γγ}-1| \le 0.04$ still allows $|μ^{331}_{Zγ}-1|$ 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$(h^0_3\rightarrow γγ)$ is very sensitive to the parameter $β$ used to distinguish different 3-3-1 models.

hep-ph↗