Kaon theory news

Abstract

During the last fifteen years Bs, d decays, B0s, d - B0s, d mixings, related mixing induced CP-violating asymmetries SψKS and Sψφ and CP violation in charm decays provided the dominant information about the pattern of flavour violation within the Standard Model (SM) and its extensions. K meson physics was solely represented by the CP-violating parameter ϵk which by itself could still provide a very powerful constraint on new physics (NP) models but could not offer by far as much information about the pattern of flavour violation in nature as the observables in heavy meson decays. We emphasize that in the coming years K meson physics will certainly strike back through the measurements of the branching ratios of theoretically very clean decays K+ → π+vv and Kl → n0 vv and improved calculations of the ratio ϵ'/ϵ provided recently by lattice QCD and large N approach. Also the improved calculations of the K0 - K̄0 mass difference ΔMk could be of help in this context. We summarize the status of K+ → π+vv and Kl → n0vv within the SM and simplified NP models and update the picture of flavour violation in the Littlest Higgs model with T-parity (LHT) taking all available constraints into account. But the highlight of this talk are new results on ϵ'/ϵ from lattice QCD and large N approach that give a strong indication for a new anomaly in flavour physics, this time coming from K mesons. Indeed, ϵ'/ϵ within the SM is found to be significantly below the data of NA48 and KTeV collaborations. Combining lattice results on the non-perturbative parameters B(1/2)6 and B(3/2)8 with the assumption that the SM dynamics dominates the ΔI = 1/2 rule a 3σ anomaly in ϵ'/ϵ emerges. Moreover, the recently derived upper bounds on B(1/2)6 and B(3/2)8 from large N approach with B(1/2)6 ≤B(3/2)8 < 1, fully consistent with lattice results, increase the confidence that the found anomaly could be an important signal of NP at work. Of particular importance are the correlations between K+ → π+vv, KL → π0vv and ϵ'/ϵ. With future precise measurements of K+ → π+vv and KL → π0 vv and improved calculations of ϵ'/ϵ they will surely provide powerful tools for selecting the favourite NP models. We illustrate this with the help of the LHT model and simplified models in which NP in K → π vv and ϵ'/ϵ is governed by Z with flavour violating couplings or by a heavy Z'.