Abstract
The chromomagnetic dipole moment (CMDM) and chromoelectric dipole moment (CEDM) of the top quark are calculated at the one-loop level in the framework of the two-Higgs doublet model with four fermion generations (4GTHDM), which is still consistent with experimental data and apart from new scalar bosons (${H}^{0}$, ${A}^{0}$, and ${H}^{\ifmmode\pm\else\textpm\fi{}}$) and quarks (${b}^{\ensuremath{'}}$ and ${t}^{\ensuremath{'}}$) predicts new sources of $CP$ violation via the extended $4\ifmmode\times\else\texttimes\fi{}4$ CKM matrix. Analytical expressions for the CMDM and CEDM of a quark are presented both in terms of Feynman parameter integrals, which are explicitly integrated, and Passarino-Veltman scalar functions, with the main contributions arising from loops carrying the scalar bosons accompanied by the third- and fourth-generation quarks. The current bounds on the parameter space of the 4GTHDM are discussed and a region still consistent with the LHC data on the 125 GeV Higgs boson and the oblique parameters is identified. It is found that the top quark CMDM, which is induced by all the scalar bosons, can reach values of the order of ${10}^{\ensuremath{-}2}--{10}^{\ensuremath{-}1}$. As for the top quark CEDM, it only receives contributions from the charged scalar boson and can reach values of the order of ${10}^{\ensuremath{-}20}--{10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{ecm}$ for relatively light ${m}_{{H}^{\ifmmode\pm\else\textpm\fi{}}}$ and heavy ${m}_{{b}^{\ensuremath{'}}}$, with the dominant contribution arising from the $b$ quark. The CEDM would be the most interesting prediction of this model as it can be larger than the value predicted by the usual THDMs by one order of magnitude.
Highlights
Since its discovery in 1995 by the CDF and D0 experiments at Fermilab’s Tevatron [1,2], the top quark has played a special role in the study of the phenomenology of the standard model (SM), which stems from the fact that its mass is of the order of the electroweak symmetry breaking scale
We have presented a calculation of the one-loop contributions to the chromomagnetic and chromoelectric dipole moments of the top quark within the two-Higgs doublet model with four fermion families, which predicts new sources of CP violation arising from the complex phases of two mixing matrices and the extended 4 × 4 CKM matrix
Unlike the standard model with a sequential fourth generation of fermions, which is already excluded by the Large Hadron Collider (LHC) data on the SM Higgs boson, there are still some regions of the parameter space of the 4GTHDM that are compatible with such data
Summary
Ingeniería en Mecatrónica, Universidad Politecnica de Puebla, Tercer Carril del Ejido Serrano s/n, San Mateo Cuanalá, Juan C. The chromomagnetic dipole moment (CMDM) and chromoelectric dipole moment (CEDM) of the top quark are calculated at the one-loop level in the framework of the two-Higgs doublet model with four fermion generations (4GTHDM), which is still consistent with experimental data and apart from new scalar bosons (H0, A0, and HÆ) and quarks (b0 and t0) predicts new sources of CP violation via the extended 4 × 4 CKM matrix. It is found that the top quark CMDM, which is induced by all the scalar bosons, can reach values of the order of 10−2–10−1. As for the top quark CEDM, it only receives contributions from the charged scalar boson and can reach values of the order of 10−20–10−19 ecm for relatively light mHÆ and heavy mb0, with the dominant contribution arising from the b quark. The CEDM would be the most interesting prediction of this model as it can be larger than the value predicted by the usual THDMs by one order of magnitude
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