581 research outputs found
Vector and axial-vector current correlators within the instanton model of QCD vacuum
The pion electric polarizability, \alpha^E_\pi^\pm, the leading order
hadronic contribution to the muon anomalous magnetic moment, ,
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
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
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
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