Radiative correction effects of a very heavy top

Abstract

If the top is very heavy, m t ≫ M Z , the dominant radiative correction effects in all electroweak precision tests can be exactly characterized in terms of two quantities, the ρ-parameter and the GIM violating Z → bb coupling. These quantities can be computed using the Standard Model Lagrangian with vanishing gauge couplings. This is done here up to two loops for arbitrary values of the Higgs mass.

Universal extra dimensions andZ→bb¯

“…In that limit the gauge bosons play the role of external sources and the only propagating fields are the quarks, the Higgs field, and the charged and neutral Goldstone bosons G ± and G 0 . As explained in [28,29] one may relate the one-loop vertex Zbb to the corresponding G 0 bb vertex by means of a Ward identity; the latter is a direct consequence of current conservation, which holds for the neutral current before and after the Higgs doublet acquires a vacuum expectation value v. In practice, carrying out the calculation in the aforementioned limit amounts to the elementary computation of the one-loop off-shell vertex G 0 bb. In the gaugeless limit and for massless b-quarks the only contribution to this vertex is depicted in Fig.…”

The m W − m Z interdependence in the Standard Model: a new scrutiny

“…Concerning the EW corrections, the leading two-loop contribution O(α 2 M 4 t /m 4 W ) to δρ was first obtained in the large top-mass limit [10], neglecting all the other masses including the Higgs mass, and then in the socalled gaugeless limit of the SM, i.e. in the limit g, g → 0 where g (g ) is the SU(2) (U(1) Y ) gauge coupling [11][12][13]. The incorporation of these effects in ∆r was addressed in ref.…”

Complete Two-Loop Electroweak Fermionic Corrections to the Effective Leptonic Weak Mixing Anglesin2θefflAwramik1, Czakon2, Freitas3 et al. 2004Phys. Rev. Lett.

“…Besides the oneloop contributions also higher-order QCD corrections [2,3] are known. However, for the electroweak two-loop corrections, only the leading term in the large M H expansion [4] and the leading [5] and subleading [6] terms in the large top quark mass expansion are available up to now. The goal of the present work is the calculation of the complete two-loop electroweak contributions with one or two closed fermion loops.…”