Yukawa enhancement of Z -mediated new physics in ∆ S = 2 and ∆ B = 2 processes

TLDR: In this article, the authors discuss Yukawa-enhanced contributions from Z-mediated new physics to down-type quark ΔF = 2 processes in the framework of the standard model gauge-invariant effective theory (SMEFT).

Abstract: We discuss Yukawa-enhanced contributions from Z-mediated new physics to down-type quark ΔF = 2 processes in the framework of the standard model gauge-invariant effective theory (SMEFT). Besides the renormalization group (RG) mixing of the Z-mediating ψ 2 H 2 D operators into ΔF = 2 operators, we include at the electroweak scale one-loop (NLO) matching corrections consistently, necessary for the removal of the matching scale dependence. We point out that the right-handed Z-mediated interactions generate through Yukawa RG mixing ΔF = 2 left-right operators, which are further enhanced through QCD RG effects and chirally enhanced hadronic matrix elements. We investigate the impact of these new effects on the known correlations between ΔF = 2 and ΔF = 1 transitions in the SMEFT framework and point out qualitative differences to previous parameterizations of Z-mediated new physics that arise for the left-handed case. We illustrate how specific models fit into our model-independent framework by using four models with vector-like quarks. We carry out model-independent analyses of scenarios with purely left-handed and purely right-handed new-physics Z couplings for each of the three sectors s → d, b → s and b → d. Specifically we discuss the correlations between e′/e, e K , $$ {K}_L\to {\mu}^{+}{\mu}^{-}{K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ and $$ {K}_L\to {\pi}^0\nu \overline{\nu} $$ in the Kaon sector, and ϕ s , B s → μ + μ − and B → K (*)(μ + μ − , $$ \nu \overline{\nu} $$ ) in the b → s sector and B d → μ + μ − in the b → d sector.