Marc Knecht

Hadronic light by light corrections to the muon g-2: The Pion pole contribution

The correction to the muon anomalous magnetic moment from the pion-pole contribution to the hadronic light-by-light scattering is considered using a description of the pi0 - gamma* - gamma* transition form factor based on the large-Nc and short-distance properties of QCD. The resulting two-loop integrals are treated by first performing the angular integration analytically, using the method of Gegenbauer polynomials, followed by a numerical evaluation of the remaining two-dimensional integration over the moduli of the Euclidean loop momenta. The value obtained, a_{mu}(LbyL;pi0) = +5.8 (1.0) x 10^{-10}, disagrees with other recent calculations. In the case of the vector meson dominance form factor, the result obtained by following the same procedure reads a_{mu}(LbyL;pi0)_{VMD} = +5.6 x 10^{-10}, and differs only by its overall sign from the value obtained by previous authors. Inclusion of the eta and eta-prime poles gives a total value a_{mu}(LbyL;PS) = +8.3 (1.2) x 10^{-10} for the three pseudoscalar states. This result substantially reduces the difference between the experimental value of a_{mu} and its theoretical counterpart in the standard model.

Hadronic light-by-light scattering contribution to the muon g - 2: An effective field theory approach

The hadronic light-by-light contribution to a(mu), the anomalous magnetic moment of the muon, is discussed from the point of view of an effective low-energy theory. As an application, the coefficient of the leading logarithm arising from the two-loop graphs involving two anomalous vertices is computed, and found to be positive. This corresponds to a positive sign for the pion-pole contribution to the hadronic light-by-light correction to a(mu), and to a sizable reduction of the discrepancy between the present experimental value of a(mu) and its theoretical counterpart in the standard model.

Resonance estimates of

Abstract. Starting from the study of the low-energy and high-energy behaviors of the QCD three-point functions

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low-energy constants and QCD short-distance constraints

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Virtual Photons in Low Energy π − π Scattering

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Electroweak hadronic contributions to the muon (g-2)

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Decay of pseudoscalars into lepton pairs and large N(c) QCD

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Patterns of spontaneous chiral symmetry breaking in the large-Nc limit of QCD-like theories

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A critical reassessment of Q7 and Q8 matrix elements

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