Abstract
Hadronic light-by-light scattering in the anomalous magnetic moment of the muon a_\muaμ is one of two hadronic effects limiting the precision of the Standard Model prediction for this precision observable, and hence the new-physics discovery potential of direct experimental determinations of a_\muaμ. In this contribution, I report on recent progress in the calculation of this effect achieved both via dispersive and lattice QCD methods.
Highlights
The magnetic moment of the muon is one of the most precisely measured quantities in particle physics.In units of e 2mμ · ħh 2, its value is given by the gyromagnetic factor g.The prediction that g = 2 was an early success of the Dirac equation, applied to the electron
The exploratory study [15] found that the LbL tensor (5) at moderate spacelike virtualities can be described by a set of resonance poles, much in the same way that aμhlbl is obtained in the model calculations
Several dispersive approaches have been proposed to handle the complicated physics of hadronic light-by-light scattering [20,21,22]
Summary
The magnetic moment of the muon is one of the most precisely measured quantities in particle physics. It is interesting to test whether all eight forward LbL amplitudes obtained from lattice computations can be described by such a sum of resonances via the dispersive sum rule Essential ingredients in this parametrization of σγ∗γ∗→hadrons are the transition form factors FMγ∗γ∗(Q21, Q22), describing the coupling of the resonance to two virtual photons. The exploratory study [15] found that the LbL tensor (5) at moderate spacelike virtualities can be described by a set of resonance poles, much in the same way that aμhlbl is obtained in the model calculations It would be worth exploring this avenue further, in particular by increasing the precision of the lattice calculation
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