Top quark decay at next-to-leading order in the standard model effective field theory

Abstract

We consider top quark decay in the Standard Model Effective Field Theory (SMEFT). We present a calculation of the total decay width and the W -boson helicity fractions at next-to-leading order (NLO) in SMEFT. Our result includes the complete set of contributing four-fermion operators in addition to QCD dipole operators and bottom-mass suppressed effects. We show that operators that first appear at NLO in the SMEFT can be bounded by the current data as well as future data from both a high-luminosity LHC and a potential e + e − collider, demonstrating the importance of going beyond leading order when studying the SMEFT. We discuss technical aspects of our calculation that we believe will be useful in future higher-order studies of the SMEFT, in particular the treatment of γ 5 in loop diagrams.

Electroweak and QCD corrections to Z and W pole observables in the standard model EFT

“…A program of calculations has begun to treat the SMEFT contributions at NLO, for both the QCD and electroweak (EW) contributions. The SMEFT QCD corrections to gauge boson pair production [11,12] and top quark production and decay [13][14][15][16] are known. The electroweak SMEFT corrections to Higgs decays to bb [17][18][19], γγ [20][21][22][23], Zγ [24,25], ZZ [24], and W W [20] have also been computed, along with partial corrections to the Drell Yan process [26].…”

Renormalization and non-renormalization of scalar EFTs at higher orders

“…[104][105][106][107][108] (see also e.g. [109] for a recent discussion in the SMEFT). Such operators are not typically associated with theories of scalars, but at high enough mass dimension a class of such operators does in fact exist, see [42,110].…”

New method for fitting coefficients in standard model effective theory

“…Following Ref. [36], we fit the coefficients C tW , C bW , C φtb , C tg , and C bg , which correspond to the operators…”

“…We make use of the expressions in Ref. [36] for SMEFT contributions to Γ tot , the total decay width to bW , F L , the fractional decay rate for a longitudinally polarized W boson, and F − , the fractional decay rate for a W boson with negative helicity. 4 We include the QCD corrections that are given in Ref.…”

“…4 We include the QCD corrections that are given in Ref. [36]. We note that the standard-model QCD corrections are also given in Ref.…”