A New Approach to Weak Amplitudes in Large-Nc QCD

Abstract

We report on some recent progress made in understanding weak matrix elements of mesons in the context of the next-to-leading order of the large-Nc approximation to QCD. Specifically, we first use the example of the weak contributions to the pi^+ - pi^0 mass difference to exhibit how a systematic matching can be achieved analytically between short distances and long distances within our large-Nc framework. We are then also able to compute matrix elements of the operator Q_7, as they turn out to depend on the same QCD correlator as the previous pion mass difference. As a final example we determine the chiral counterterms governing the pseudoscalar decay into a lepton pair, where we briefly comment also on the special case K_L -> mu^+ mu^-.

15 pages, 4 figures. LateX. This report covers the material presented by the authors in three separate talks at the QCD'99 conference in Montpellier

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• QCD Short-distance Constraints and Hadronic Approximations
• Final State Interactions in Kaon Decays
• New QCD estimate of the kaon penguin matrix elements and epsilon'/epsilon
• A Critical Reassessment of Q7 and Q8 Matrix Elements
• Novel patterns for vector mesons from the large-Nc limit
• An example of resonance saturation at one loop
• Light Hadron Weak Matrix Elements
• Charged Kaon K \to 3 pi CP Violating Asymmetries at NLO in CHPT
• Minimal Hadronic Ansatz to Large-Nc QCD and Hadronic tau Decay
• epsilon'/epsilon in the Standard Model
• Relations between vacuum condensates and low energy parameters from a rational approach
• Chiral Limit Prediction for epsilon'/epsilon at NLO in 1/N_c
• Form factor in K+ --> pi+ pi0 gamma: interference versus direct emission
• B_K in the chiral limit within the 1/Nc expansion
• Theoretical status of epsilon'/epsilon