Singularity-free Next-to-leading Order $ΔS= 1$ Renormalization Group Evolution and $ε_{K}^{\prime}/ε_{K}$ in the Standard Model and Beyond

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 $ε_K^{\prime}$, the measure of direct $CP$ violation in $K\to ππ$ decays. Using our new RG evolution and the latest lattice results for the hadronic matrix elements, we calculate the ratio $ε_{K}^{\prime}/ε_{K}$ (with $ε_{K}$ quantifying indirect $CP$ violation) in the Standard Model (SM) at NLO to $ε_{K}^{\prime}/ε_{K} = (1.06 \pm 5.07) \times 10^{-4}$, 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 $α_{EM}^2/α_s^2$, which is numerically unimportant for the SM case but should be included in studies of high-scale new-physics.

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