Rare top-quark decays t → cg( g) in the aligned two-Higgs-doublet model

摘要

We update the Standard Model (SM) predictions for the branching ratios of the rare top-quark decays t -> cg(g), and evaluate the maximum rates that can be reached in the aligned as well as in the four conventional two-Higgs-doublet models (2HDMs) with Z(2) symmetries. Taking into account the relevant constraints on the model parameters resulting from a global fit obtained at the 95.5% confidence level, we find that the branching ratios of t -> cg and t. cgg decays can reach up to 3.36 x 10(-9) and 2.95 x 10(-9) respectively, being therefore of the same order, in the aligned 2HDM (A2HDM). This is obviously different from the SM case, where the predicted branching ratio of the three-body decay t -> cgg is about two orders of magnitude larger than that of the two-body decay t -> cg. On the other hand, compared with the SM predictions, no significant enhancements are observed in the four conventional 2HDMs withZ(2) symmetries for the branching ratios of these two decays. Nevertheless, the predicted branching ratios of t -> cg and t -> cgg decays in the A2HDM are still out of the expected sensitivities of the future high-luminosity Large Hadron Collider and the Future Circular Collider in hadronhadron mode.

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