Abstract
Extensions to the Standard Model that use strictly off-shell degrees of freedom---the fakeons---allow for new measurable interactions at energy scales usually precluded by the constraints that target the on-shell propagation of new particles. Here we employ the interactions between a new fake scalar doublet and the muon to explain the recent Fermilab measurement of its anomalous magnetic moment. Remarkably, unlike in the case of usual particles, the experimental result can be matched for fakeon masses below the electroweak scale without contradicting the stringent precision data and collider bounds on new light degrees of freedom. Our analysis, therefore, demonstrates that the fakeon approach offers unexpected viable possibilities to model new physics naturally at low scales.
Highlights
The longstanding anomaly concerning the magnetic moment of the muon, aμ 1⁄4 ðg − 2Þμ=2, is generally interpreted as the effect of new degrees of freedom that, coupling to the muon, leave their imprint in this precision observable
The presence of an anomaly in ðg − 2Þμ is supported by the final result of the Brookhaven E821 experiment [1], aEμ821 1⁄4 116592089ð63Þ × 10−11, which gives rise to a 3.7σ deviation ΔaEμ821 1⁄4 aEμ821 − aSμM 1⁄4 ð279 Æ 76Þ × 10−11 when confronted with the worldwide consensus of the SM contribution [2], aSμM 1⁄4 116591810ð43Þ × 10−11
We have proposed a new solution to the puzzle of the muon anomalous magnetic moment by modelling the physics beyond the SM with purely virtual degrees of freedom: the fakeons
Summary
The longstanding anomaly concerning the magnetic moment of the muon, aμ 1⁄4 ðg − 2Þμ=2, is generally interpreted as the effect of new degrees of freedom that, coupling to the muon, leave their imprint in this precision observable. AμFlþE821 1⁄4 116592061ð41Þ × 10−11; ð2Þ leads to a 4.2σ discrepancy with the theory prediction: ΔaμFlþE821 1⁄4 aFμlþE821 − aSμM 1⁄4 ð251 Æ 59Þ × 10−11: ð3Þ This significant deviation could be explained by not yet understood low-energy hadronic physics [5], or, as we propose, by new physics contributions. To this purpose, we address the ðg − 2Þμ problem in a new framework that overcomes the limitations of conventional model building by relying on new, strictly-virtual, degrees of freedom: the fakeons. We consider an extension of the SM that contains a new fake scalar doublet The latter does not acquire a vacuum expectation value (VEV) and, besides the gauge and Higgs bosons, couples significantly only to muons. The fakeon prescription can be used to consistently include fake ghost particles in the theory and prevent their on-shell propagation
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