Singularity-free next-to-leading order ΔS = 1 renormalization group evolution and ϵK′/ϵK in the Standard Model and beyond
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- Kitahara, T., Nierste, U. & Tremper, P. J. High Energ. Phys. (2016) 2016: 78. doi:10.1007/JHEP12(2016)078
The standard analytic solution of the renormalization group (RG) evolution for the ΔS = 1 Wilson coefficients involves several singularities, which complicate analytic solutions. In this paper we derive a singularity-free solution of the next-to-leading order (NLO) RG equations, which greatly facilitates the calculation of ϵK′, the measure of direct CP violation in K → ππ decays. Using our new RG evolution and the latest lattice results for the hadronic matrix elements, we calculate the ratio ϵK′/ϵK (with ϵK quantifying indirect CP violation) in the Standard Model (SM) at NLO to ϵK′/ϵK = (1.06 ± 5.07) × 10− 4, which is 2.8 σ below the experimental value. We also present the evolution matrix in the high-energy regime for calculations of new physics contributions and derive easy-to-use approximate formulae. We find that the RG amplification of new-physics contributions to Wilson coefficients of the electroweak penguin operators is further enhanced by the NLO corrections: if the new contribution is generated at the scale of 1-10 TeV, the RG evolution between the new-physics scale and the electroweak scale enhances these coefficients by 50-100%. Our solution contains a term of order αEM2/αs2, which is numerically unimportant for the SM case but should be included in studies of high-scale new-physics.