Lepton flavor-changing scalar interactions and $g-2$ of the muon

Y.-F. Zhou; Y.-L. Wu

doi:doi:10.1140/epjc/s2003-01137-1

EPJ

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2024 Impact factor 4.8

Particles and Fields

Eur. Phys. J. C 27, 577-585 (2003)
DOI: 10.1140/epjc/s2003-01137-1

Lepton flavor-changing scalar interactions and g-2 of the muon

Y.-F. Zhou¹ and Y.-L. Wu²

¹ Ludwig-Maximilians-Universität München, Sektion Physik, Theresienstraße 37, 80333 München, Germany
² Institute of Theoretical Physics, Chinese Academy of Science, Beijing 100080, P.R. China

(Received: 5 September 2002 / Revised version: 11 January 2003 / Published online: 26 February 2003 )

Abstract
A systematic investigation on the muon's anomalous magnetic moment and a related lepton flavor-violating process such as $\mu \to e\gamma$ , $\tau\to e\gamma$ and $\tau\to \mu \gamma$ is made at the two-loop level in the models with flavor-changing scalar interactions. The two-loop diagrams with double scalar exchanges are studied and their contributions are found to be compatible with the ones from the Barr-Zee diagram. By comparing with the latest data, the allowed ranges for the relevant Yukawa couplings Y_ij in the lepton sector are obtained. The results show the hierarchical structure $Y_{\mu e, \tau e} \ll Y_{\mu \tau} \simeq Y_{\mu\mu}$ in the physical basis if $\Delta a_{\mu}$ is found to be $>50\times 10^{-11}$ . It deviates from the widely used ansatz in which the off-diagonal elements are proportional to the square root of the products of the related fermion masses. An alternative Yukawa coupling matrix in the lepton sector is suggested to understand the current data. With such a reasonable Yukawa coupling ansatz, the decay rate of $\tau\to \mu \gamma$ is found to be near the current experiment upper bound.