1,798 research outputs found

    Muon g-2, rare decays P \to l^+l^- and transition form factors P \to \gamma\gamma^*

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    Measuring the muon anomalous magnetic moment g-2 and the rare decays of light pseudoscalar mesons into lepton pair P \to l+l- serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model predictions the data on the transition form factors of light pseudoscalar mesons play significant role. Recently new data on behavior of these form factors at large momentum transfer was supplied by the BABAR collaboration. We comment on the (in)consistency of these data with perturbative QCD expectation.Comment: 4 pages, 3 figures, invited talk at the 3rd Joint International Hadron Structure'09 Conference, Tatranska Strba (Slovak Republic), Aug. 30--Sept. 3, 2009; v2 - some typos are correcte

    Vector and axial-vector current correlators within the instanton model of QCD vacuum

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    The pion electric polarizability, \alpha^E_\pi^\pm, the leading order hadronic contribution to the muon anomalous magnetic moment, aμhvp1a_\mu^{hvp 1} , and the ratio of the difference to the sum of vector and axial-vector correlators, (V-A)/(V+A), are found within the instanton model of QCD vacuum. The results are compared with phenomenological estimates of these quantities following from the ALEPH and OPAL data on vector and axial-vector spectral densities.Comment: 5 pages, 1 figure, talk given at the 16th Intern. Spin Physics Symposium, SPIN2004, Trieste, Italy (October 10-16, 2004

    Adler function and hadronic contribution to the muon g-2 in a nonlocal chiral quark model

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    The behavior of the vector Adler function at spacelike momenta is studied in the framework of a covariant chiral quark model with instanton-like quark-quark interaction. This function describes the transition between the high energy asymptotically free region of almost massless current quarks to the low energy hadronized regime with massive constituent quarks. The model reproduces the Adler function and V-A correlator extracted from the ALEPH and OPAL data on hadronic \tau lepton decays, transformed into the Euclidean domain via dispersion relations. The leading order contribution from hadronic part of the photon vacuum polarization to the anomalous magnetic moment of the muon, a_\mu^{hvp,1}, is estimated.Comment: 20 pages, 9 figure

    Singlet VA \tilde V correlator within the instanton vacuum model

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    The correlator of singlet axial-vector and vector currents in the external electromagnetic field is studied within the instanton liquid model of QCD vacuum. In the chiral limit we calculate the longitudinal w_L^0 and transversal w_T^0 with respect to axial-vector index invariant amplitudes at arbitrary momentum transfer q. It is demonstrated how the anomalous longitudinal part of the correlator is renormalized at low momenta due to the presence of the U_A(1) anomaly.Comment: 9 pages, 4 figure