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

Abstract

We update the Standard Model (SM) predictions for the branching ratios of the rare top-quark decays $$t \rightarrow cg(g)$$ t → c g ( 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 $$\mathcal {Z}_2$$ Z 2 symmetries. Taking into account the relevant constraints on the model parameters resulting from a global fit obtained at the $$95.5\%$$ 95.5 % confidence level, we find that the branching ratios of $$t \rightarrow cg$$ t → c g and $$t \rightarrow cgg$$ t → c g g decays can reach up to $$3.36\times 10^{-9}$$ 3.36 × 10 - 9 and $$2.95\times 10^{-9}$$ 2.95 × 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 $$t \rightarrow cgg$$ t → c g g is about two orders of magnitude larger than that of the two-body decay $$t \rightarrow cg$$ t → c g . On the other hand, compared with the SM predictions, no significant enhancements are observed in the four conventional 2HDMs with $$\mathcal {Z}_2$$ Z 2 symmetries for the branching ratios of these two decays. Nevertheless, the predicted branching ratios of $$t \rightarrow cg$$ t → c g and $$t \rightarrow cgg$$ t → c g g 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 hadron-hadron mode.

Top-quark FCNC decays, LFVs, lepton g − 2, and W mass anomaly with inert charged Higgses

“…Thus, if any signal in these processes is detected in experiments, it definitely indicates new physics effects at play. Some interesting extensions of the SM proposed to enhance the top-FCNC decays can be found in [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Rare top quark decays in the minimal R-symmetric supersymmetric standard model

“…For example, the two-Higgs doublet models (2HDM) [11][12][13][14][15][16], the minimal supersymmetric standard model (MSSM) [17][18][19][20][21][22][23][24][25][26][27][28], the littlest Higgs model with T-parity (LHT) [29][30][31], the left-right supersymmetric model [32], the topcolor-assisted technicolor model (TC2) [33],…”