Probing Scalar and Pseudoscalar Solutions of the g-2 Anomaly

TL;DR

This paper explores scalar and pseudoscalar particle models as potential solutions to the g-2 anomaly, analyzing experimental constraints and identifying a small viable mass window for future experiments.

Contribution

It provides a comprehensive analysis of experimental constraints on scalar and pseudoscalar solutions to the g-2 anomaly within 1 MeV to 40 GeV, highlighting a narrow remaining viable mass window.

Findings

Most of the parameter space is excluded by existing experiments.

A small mass window between ~30 MeV and 200 MeV remains viable.

Future experiments like NA64 can probe this remaining window.

Abstract

I investigate a class of models with scalar and pseudoscalar solutions to the g-2 anomaly in the mass range between 1 MeV and 40 GeV. In particular, I investigate the constraints from BaBar, beam dump experiments and from Z decay measured quantities. I find that most of the favored region in this mass range is excluded except for a small window between ~30 MeV and 200 MeV. This open window is expected to be covered by the proposed NA64 experiment. The results can be readily applied to other proposed solutions of the anomaly, such as solutions with Z0 or with the dark photon.