Sensitivity to new physics: a_e vs. a_mu

TL;DR

This paper proposes a new tree-level mechanism for new physics contributions to leptonic magnetic moments, showing a linear mass dependence that enhances the sensitivity of the electron magnetic moment to potential new physics effects.

Contribution

It introduces an alternative tree-level contribution mechanism for a_l with linear mass dependence, contrasting the traditional quadratic dependence in quantum loop effects.

Findings

Linear dependence on lepton mass increases a_e sensitivity to new physics

Tree-level contributions can dominate over loop effects in certain models

Potential for improved detection of new physics via electron magnetic moment

Abstract

At present it is generally believed that ``new physics'' effects contribute to leptonic anomalous magnetic moment, a_l, via quantum loops only and they are proportional to the squared lepton mass, (m_l)^2. An alternative mechanism for a contribution by new physics is proposed. It occurs at the tree level and exhibits a linear rather than quadratic dependence on m_l. This leads to a much larger sensitivity of a_e to the new physics than was expected so far.