Kaon Theory News
(Oct 1, 2015)Abstract
During the last fifteen years B\_s,d decays, B\_s,d^0-B^0\_s,d
mixings, CP-violating asymmetries S\_K\_S and S\_\psi\phi provided the
dominant information about the pattern of flavour violation within the SM and
its extensions. 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^+->pi^+\nu\barand K\_L->\pi^0\nu\bar\nu
and improved calculations of the ratio epsilon'/epsilon=\epe. We summarize the
status of K^+->pi^+\nu\barand K\_L->\pi^0\nu\barwithin the SM and
simplified NP models and update the picture of flavour violation in the
Littlest Higgs model with T-parity taking all available constraints into
account. But the highlight of this talk are new results on 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, within the SM is
found to be significantly below the data of NA48 and KTeV collaborations.
Combining lattice results on the non-perturbative parameters B6 and B8 with the
assumption that the SM dynamics dominates the Delta I=1/2 rule a 3 sigma
anomaly in emerges. Moreover, the recently derived upper bounds on B6 and
B8 from large N approach increase the confidence that the found anomaly could
be an important signal of NP at work. Of particular importance are the
correlations between K^+->pi^+\nu\bar\nu, K\_L->\pi^0\nu\barand \epe. With
future precise measurements of K^+->pi^+\nu\barand K\_L->\pi^0\nu\barand
improved calculations of 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\to\pi\nu\barand is
governed by Z with flavour violating couplings or by a heavy Z'.