UWThPh-2001-39 Comment on ‘Analysis of O(p 2) Corrections to 〈ππ|Q7,8|K〉’

Analysis of O(p 2) Corrections to 〈ππ|Q7,8|K〉

Determination of 〈(ππ)I=2|Q7,8|K〉 in the Chiral Limit

We reconsider the dispersive evaluation of the weak matrix elements 〈(ππ)I=2|Q7,8|K〉 in the chiral limit. The perturbative matching is accomplished fully within the scheme dependence used in the two loop weak OPE calculations. The effects of dimension eight (and higher dimension) operators are fully accounted for. We perform a numerical determination of the weak matrix elements using our disper...

ar X iv : h ep - p h / 02 09 33 2 v 1 2 7 Se p 20 02 1 K → ππ Electroweak Penguins in the Chiral Limit

We report on dispersive and finite energy sum rule analyses of the electroweak penguin matrix elements (ππ)2|Q7,8|K 0 in the chiral limit. We accomplish the correct perturbative matching (scale and scheme dependence) at NLO in αs, and we describe two different strategies for numerical evaluation.

Electroweak Penguins and Large N C

I review the progress made in the calculation of the electroweak penguins Q7,8 in the framework of the Hadronic Approximation to large-Nc QCD, and give an update of results. A nonzero value of ǫ ′ /ǫ signals the existence of direct CP violation in the decay K → ππ and is a measure of the amount of CP violation in the Standard Model. At present the world average is given by 1 ǫ ′ ǫ = (16.6 ± 1.6...

Electromagnetic corrections to γπ ± → π 0 π ±

The amplitude for the anomalous transitions γπ → ππ is analyzed within Chiral Perturbation Theory including electromagnetic interactions. The presence of a t-channel one-photon exchange contribution induces sizeable O(e2) corrections which enhance the cross-section in the threshold region and bring the theoretical prediction into agreement with available data. In the case of the crossed reactio...