The Muon Anomalous Magnetic Moment: A Harbinger For "New Physics"

TL;DR

This paper analyzes the muon anomalous magnetic moment $a_BM$ as a sensitive probe of new physics. It decomposes the Standard Model prediction into QED, hadronic, and electroweak contributions, highlighting hadronic uncertainties as the dominant limitation and presenting a SM value near $a_BM^{\rm SM} \approx 1.1659\times 10^{-4}$ with a reported experimental deviation of about $2.6\sigma$. The authors explore New Physics explanations, with supersymmetric loop effects (large $\tan\beta$ and moderate superpartner masses) and radiative muon-mass models providing natural mechanisms to account for the observed discrepancy, potentially locating new physics at the TeV scale. They also discuss alternative NP scenarios (anomalous $W$ properties, extra gauge bosons) and conclude that forthcoming experimental and theoretical refinements are crucial to determine if the deviation is a harbinger of new physics. The outlook emphasizes coordinated improvements in $a_Bmu^{\rm exp}$ and $a_Bmu^{\rm SM}$ and the significant implications for collider and flavor-violation programs should the hint persist.

Abstract

QED, Hadronic, and Electroweak Standard Model contributions to the muon anomalous magnetic moment, a_mu = (g_mu-2)/2, and their theoretical uncertainties are scrutinized. The status and implications of the recently reported 2.6 sigma experiment vs.theory deviation a_mu^{exp}-a_mu^{SM} = 426(165) times 10^{-11} are discussed. Possible explanations due to supersymmetric loop effects with m_{SUSY} \simeq 55 sqrt{tan beta} GeV, radiative mass mechanisms at the 1--2 TeV scale and other ``New Physics'' scenarios are examined.

Figures (6)

• Figure 1: Leading hadronic vacuum polarization corrections to $a_\mu$.
• Figure 2: One-loop electroweak radiative corrections to $a_\mu$.
• Figure 3: Supersymmetric loops contributing to the muon anomalous magnetic moment.
• Figure 4: Example of a pair of one-loop diagrams which can induce a finite radiative muon mass.
• Figure 5: Potential diagrams that can contribute to the anomalous magnetic moment in radiative muon mass models.