Chromomagnetic and chromoelectric dipole moments of the top quark in the fourth-generation THDM

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 ± ) and quarks (b and t ) predicts new sources of CP violation via the extended 4 × 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 −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 m H ± and heavy m b , 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.

Flavor violation in chromo- and electromagnetic dipole moments induced by Z′ gauge bosons and a brief revisit of the Standard Model

“…In addition, appreciable new physics effects on the top CEDM are of great importance as they would directly impact the CP-violation phenomenon, which would be indicative of new sources of CP violation and, in our case, of FV. Currently, the spin correlations of top-antitop pairs and the polarization of the top quark have been measured in pp collisions at ffiffi ffi s p ¼ [31] as well as in other extensions such as the two-Higgs doublet model [32], the minimal supersymmetric Standard Model [33,34], 3-3-1 models [35], technicolor models [36], models with vectorlike multiplets [37], effective operators [38], and the two-Higgs doublet model with four fermion generations [39]. However, the SM CMDM contribution of the top quark coming from the three-gluon vertex is in fact divergent when the gluon is on shell, but in Ref.…”

Chromomagnetic and chromoelectric dipole moments in the 4GTHDM

“…See for instance Ref. [12], where we performed the calculation of the electroweak contribution to the CMDM of quarks in the conventional linear R ξ gauge and verified that the gauge parameter ξ drops out from the result. Furthermore, the dipole form factors cannot receive contributions from self-energy diagrams, which are required to cancel gauge dependent terms appearing in the monopolar terms via the PT approach.…”

“…In summary, the real part of the new contribution of the RM331 can be of the same order of magnitude than the real part of the pure electroweak contribution of the SM [12]. Therefore the RM331 could give a contribution larger than the ones arising in other extension models (see for instance Ref.…”

“…As far as the theoretical predictions are concerned, in the SM the CMDM is induced at the one-loop level or higher orders via electroweak (EW) and QCD contributions, whereas the CEDM can arise up to the three-loop level [6][7][8]. The SM contributions toμ t have been already studied in [9][10][11], and more recently a new evaluation was presented to address some ambiguities of previous calculations [12,13]. Since both the top quark CMDM and CEDM could receive a considerable enhancement by new physics contributions, several calculations have been reported in the literature within the framework of extension theories such as two-Higgs doublet models (THDMs) [14], the four-generation THDM [15], models with a heavy Z gauge boson [11], little Higgs models [16,17], the minimal supersymmetric standard model (MSSM) [18], unparticle models [19], vector like multiplet models [20], etc.…”

Confronting the fourth generation two-Higgs-doublet model with the phenomenology of heavy Higgs bosons

“…Reference [6] showed that the type-II 2HDM with a sequential fourth generation satisfies not only the Higgs signal strength measurements but also the oblique parameters ΔS and ΔT. Follow-up studies focused on top-quark dipole moments [13], dark matter [14], and lepton flavor changing in the Higgs boson decays [15].…”