Chromomagnetic and chromoelectric dipole moments in the 4GTHDM

Abstract

The one-loop contributions to the chromomagnetic dipole momentμt(q 2) and electric dipole momentdt(q 2) of the top quark are calculated within the reduced 331 model (RM331) in the general case of an off-shell gluon. It is argued that the results are gauge independent for q 2 = 0 and represent valid observable quantities. In the RM331μt(q 2) receives new contributions from two heavy gauge bosons Z and V + and a new neutral scalar boson h2, along with a new contribution from the standard model Higgs boson via flavor changing neutral currents. The latter, which are also mediated by the Z gauge boson and the scalar boson h2, can give a non-vanishingdt provided that there is a CP-violating phase. The analytical results are presented in terms of both Feynman parameter integrals and Passarino-Veltman scalar functions, which are useful to cross-check the numerical results. Bothμt(q 2) anddt are numerically evaluated for parameter values still allowed by the constraints from experimental data. It is found that the new one-loop contributions of the RM331 toμt(q 2) are of the same order of magnitude or larger than in other standard model extensions, with the dominant contribution arising from the V + gauge boson for q in the 30-1000 GeV interval and a mass mV of the order of a few hundreds of GeVs. As fordt(q 2), it receives the largest contribution from h2 exchange and can reach values of the order of 10 −20 , which is smaller than the contributions predicted by other standard model extensions.