Hadronic light-by-light contribution to $a_\mu$: extended Nambu-Jona-Lasinio, chiral quark models and chiral Lagrangians

TL;DR

This paper reviews and extends calculations of the hadronic light-by-light contribution to the muon g-2, incorporating various meson exchanges, quark loops, and pion effects with recent updates and unpublished insights.

Contribution

It provides an extended analysis of the hadronic light-by-light contribution using Nambu-Jona-Lasinio, chiral quark models, and chiral Lagrangians, including new considerations for connected contributions and polarizability effects.

Findings

Possible large enhancement in $ ext{π}^0$-exchange with connected contributions.

Updated estimates for quark-loop contributions.

Inclusion of effects from $a_1$ and polarizability in pion-loop analysis.

Abstract

This talk discusses our old work on the hadronic light-by-light contribution to the muon anomalous magnetic moment and some more recent contributions. I discuss the various contributions starting with pseudo-scalar meson exchange, the quark- and pion-loop, as well as scalar and $a_1$-exchange. For the $\pi^0$-exchange I point out a possible large enhancement when only connected contributions are included. For the quark-loop I include some comments about the more recent estimates of this contribution. The pion-loop is discussed in more detail, in particular I discuss our unpublished work on including effects from $a_1$ and the polarizability.