Flavor-violating ALPs, electron g−2 , and the Electron-Ion Collider

We revisit the possibility that light axionlike particles (ALPs) with lepton-flavor-violating couplings could give significant contributions to the electron’s anomalous magnetic moment <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi>g</a:mi></a:mrow><a:mrow><a:mi>e</a:mi></a:mrow></a:msub><a:mo>−</a:mo><a:mn>2</a:mn></a:mrow></a:math>. Unlike flavor diagonal lepton-ALP couplings, which are exclusively axial, lepton-flavor-violating couplings can have arbitrary chirality. Focusing on the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>e</c:mi><c:mtext>−</c:mtext><c:mi>τ</c:mi></c:mrow></c:math> ALP coupling, we find that the size of the contribution to <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi>g</e:mi><e:mi>e</e:mi></e:msub><e:mo>−</e:mo><e:mn>2</e:mn></e:math> depends strongly on the chirality of the coupling. A significant part of the parameter space for which such a coupling can explain experimental anomalies in <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:msub><g:mi>g</g:mi><g:mi>e</g:mi></g:msub><g:mo>−</g:mo><g:mn>2</g:mn></g:math> can be probed at the Electron-Ion Collider, which is uniquely sensitive to the chirality of the coupling using the polarization of the electron beam. Published by the American Physical Society 2024