Width effects on near threshold decays of the top quarkt→cWW,cZZand of neutral Higgs bosons

Abstract

The nonzero widths of heavy particles become significant when they appear in the final state of any decay occurring just around its kinematical threshold. To take into account such effects, a procedure, called the convolution method, was proposed by Altarelli, Conti and Lubicz. We expand their study which included only threshold effects for t → bW Z in the standard model. We discuss finite width effects in the three body decays t → cW W, cZZ and A 0 (h 0 ) → tbW in the type III version of a two Higgs doublet model. In particular, we find a substantial enhancement in the decay t → cZZ, which brings its branching ratio to BR(t → cZZ) ∼ 10 −3 , and in the decay A 0 → tbW , which, unlike the h 0 case, becomes competitive with the A 0 two-body decay modes.

Rare decay of the topt→cggin the standard model

“…These three body decays are suppressed with respect to two-body decays in the SM but some of them get comparably large within models of NP, such as two-Higgs-Doublet [11], especially after including finite-width effects [10].…”

Factorization in the model of unstable particles with continuous masses

“…Using the factorization method one can describe complicated decay-chain and scattering processes in a simple way. The same results could be obtained as approximations within the framework of the standard treatment, such as the narrow-width approximation [24,32], convolution method [33][34][35][36][37][38], decay-chain method [33], and semianalytical approach [24]. All of these approximations get a strict analytical formulation within the framework of the factorization method.…”

“…Also, it should be noted that there is no unique definition of the UP propagators in the literature. For example, the following expressions are used instead of P (1) µν ( ): µν − µ ν /( − Γ/2) 2 [33], µν − µ ν /( 2 − Γ) [34], and P (1) µν ( ) ( 2 )+ µ ν / 2 ( 2 ) [54]. It should be emphasized that the structures (10) and (11) are not constrained by the choice of the gauge.…”

“…In order to overcome these obstacles, some approximation schemes and methods have been worked out. For instance, double-pole approximation (DPA) [25][26][27]53], pinch-technique method [28,29], complex-mass scheme (CMS) [30,31], semi-analytical approximation [24], narrow-width approximation (NWA) [24,32], convolution method (CM) [33][34][35][36][37][38], etc. At the same time, alternative ways to deal with UPs were developed, such as effective theories of UP's [39,40], modified perturbation theory [10,21] and models with continuous mass spectrum [41,[55][56][57][58][59][60].…”

Top quark flavor-changing neutral-current decay to a 125 GeV Higgs boson in the littlest Higgs model withTparity

“…Besides, three-body FCNC decays of the top quark were also found to be a sensitive probe of the new physics, such as t → cX 1 X 2 (X = g, γ, Z, H) [11][12][13]. Very recently, ATLAS collaboration has measured the top quark decays t → cH with H → γγ and set the upper limit on the tcH coupling as 0.17 [14].…”