We present the current Standard Model (SM) prediction for the muon anomalous magnetic moment, $a_μ$, updating the first White Paper (WP20) [1]. The pure QED and electroweak contributions have been further consolidated, while hadronic contributions continue to be responsible for the bulk of the uncertainty of the SM prediction. Significant progress has been achieved in the hadronic light-by-light scattering contribution using both the data-driven dispersive approach as well as lattice-QCD calculations, leading to a…

Abstract We present results for single axial-vector and scalar meson pole contributions to the hadronic light-by-light scattering (HLbL) part of the muon’s anomalous magnetic moment. In the dispersive approach to these quantities (in narrow width approximation) the central inputs are the corresponding space-like electromagnetic transition form factors. We determine these directly using a functional approach to QCD by Dyson–Schwinger and Bethe–Salpeter equations in the very same setup we used previously to determin…

The form factor $F_{3π}(s,t,u)$ for the anomalous process $γ^\ast π\rightarrow ππ$ is calculated in the isospin limit for several values of the light current-quark mass (i.e., the pion mass) using Dyson-Schwinger and Bethe-Salpeter equations. Beyond a quark interaction kernel representing gluon-mediated interactions, leading beyond-rainbow-ladder effects at low energies are incorporated by back-coupling pions as explicit degrees of freedom. Building upon an earlier calculation of the quark-photon vertex that captu…

We present quantitative results for masses and the internal structure of four-quark states with two heavy quarks, i.e., <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi>Q</a:mi><a:msup><a:mi>Q</a:mi><a:mo>′</a:mo></a:msup><a:mover accent="true"><a:mi>q</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:msup><a:mover accent="true"><a:mi>q</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:mo>′</a:mo></a:msup></a:mrow></a:math> with <g:math xmlns:g="http://www.w3.org/1998/Math/MathML…

Five-point functions and five-body wave functions play an important role in many areas of nuclear and particle physics, e.g., in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>2</a:mn><a:mo stretchy="false">→</a:mo><a:mn>3</a:mn></a:math> scattering processes, in the five-gluon vertex, or in the study of pentaquarks. In this work we consider the permutation group <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:msub><d:mi>S</d:mi><d:mn>5</d:mn></d:msub></d:math>…