Eighth-order vacuum-polarization function formed by two light-by-light-scattering diagrams and its contribution to the tenth-order electron<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>g</mml:mi><mml:mo>−</mml:mo><mml:mn>2</mml:mn></mml:math>

Abstract

We have evaluated the contribution to the anomalous magnetic moment of the electron from six tenth-order Feynman diagrams which contain eighth-order vacuum-polarization function formed by two light-by-light-scattering diagrams connected by three photons. The integrals are constructed by two different methods. In the first method the subtractive counter terms are used to deal with ultraviolet (UV) singularities together with the requirement of gauge invariance. In the second method, the Ward-Takahashi identity is applied to the light-by-light-scattering amplitudes to eliminate UV singularities. Numerical evaluation confirms that the two methods are consistent with each other within their numerical uncertainties. Combining the two results statistically and adding small contribution from the muons and/or tau leptons, we obtain 0.000 399 9 (18) $(\ensuremath{\alpha}/\ensuremath{\pi}{)}^{5}$. We also evaluated the contribution to the muon $g\ensuremath{-}2$ from the same set of diagrams and found $\ensuremath{-}1.263\text{ }44\text{ }(14)$ $(\ensuremath{\alpha}/\ensuremath{\pi}{)}^{5}$.