Probing new light scalars with the lepton anomalous magnetic moment and the weak equivalence principle violation

TL;DR

This paper investigates how a new light scalar particle could explain anomalies in lepton magnetic moments and violate the weak equivalence principle, deriving constraints from recent experiments and proposing a favored scalar-muon-electron coupling relationship.

Contribution

It provides one-loop calculations of scalar contributions to lepton magnetic moments and derives improved experimental constraints on scalar couplings.

Findings

Constraints on scalar-lepton and scalar-photon couplings are significantly improved.

The scalar-muon-electron coupling scaling relationship is supported by experimental data.

The minimal scalar extension of the standard model is favored and tightly constrained.

Abstract

A new scalar particle with generic couplings to the standard-model particles is a possible source for the lepton anomalous magnetic moment and the violation of the weak equivalence principle. Here, one-loop contributions to the lepton anomalous magnetic moment, involving the scalar-photon and scalar-lepton couplings, are calculated. Then, employing the recent experimental results of the electron anomalous magnetic moment, the muon anomalous magnetic moment, and the MICROSCOPE mission, we find the improved constraints on scalar-lepton and scalar-photon couplings: $|\lambda_e|\leq 6.0 \times 10^{-6}$, $|\lambda_\mu|\leq 3.5\times 10^{-4}$, and $|\lambda_\gamma|\leq 4.5 \times 10^{-13}$ ${\rm eV^{-1}}$ for scalar mass below $10^4$ eV. We find that the naive scaling relationship between the scalar-muon coupling and the scalar-electron coupling is favored by three experimental results. Furthermore, the minimal standard-model extension by one scalar is also favored by all three experiments, and the model parameter is constrained best to $|\mathcal{A}|\leq 1.7 \times 10^{-11}$ eV for $m_{\phi}< 10^{-13}$ eV.