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arXiv · hep-ph/0305104

Delta I=1/2 and epsilon'/epsilon in Large-Nc QCD

T. Hambye·S. Peris·E. de Rafael
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Abstract

We present new results for the matrix elements of the Q_6 and Q_4 penguin operators, evaluated in a large-Nc approach which incorporates important O(N_c^2\frac{n_f}{N_c}) unfactorized contributions. Our approach shows analytic matching between short- and long-distance scale dependences within dimensional renormalization schemes, such as MS-bar. Numerically, we find that there is a large positive contribution to the Delta I =1/2 matrix element of Q_6 and hence to the direct CP-violation parameter epsilon'/epsilon. We also present results for the Delta I = 1/2 rule in K -> pi pi amplitudes, which incorporate the related and important ``eye-diagram'' contributions of O(N_c^2\frac{1}{N_c}) from the Q_2 operator (i.e. the penguin-like contraction). The results lead to an enhancement of the Delta I = 1/2 effective coupling. The origin of the large unfactorized contributions which we find is discussed in terms of the relevant scales of the problem.

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T. Hambye, S. Peris, E. de Rafael. 2003-05-30. Delta I=1/2 and epsilon'/epsilon in Large-Nc QCD. https://doi.org/10.1088/1126-6708%2F2003%2F05%2F027

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