Confronting spin-3/2 and other new fermions with the muon g-2 measurement

TL;DR

This paper evaluates the impact of hypothetical spin-3/2 fermions on the muon g-2 measurement, establishing constraints on their properties and comparing their effects to other new fermions in particle physics models.

Contribution

It introduces an effective field theory framework to analyze spin-3/2 fermion contributions to muon g-2 and derives new constraints on their properties, contrasting with other fermions.

Findings

Spin-3/2 fermions produce small contributions to muon g-2.

Constraints on spin-3/2 fermion mass and couplings are established.

Compared effects of spin-3/2 fermions with spin-1/2 counterparts.

Abstract

The new measurement of the muon's anomalous magnetic moment released by the Muon g-2 experiment at Fermilab sets strong constraints on the properties of many new particles. Using an effective field theory approach to the interactions of higher-spin fields, we evaluate the contribution of an electrically neutral and colour singlet spin-3/2 fermion to $(g-2)_\mu$ and derive the corresponding constraints on its mass and couplings. These constraints are then compared with the ones on spin-1/2 fermions, such as the vector-like leptons that are predicted by various extensions of the Standard Model, the excited leptons which appear in composite models, as well as the charginos and neutralinos of supersymmetric theories. Unlike these new spin-1/2 fermions, the spin-3/2 particles generate only small contributions to the muon anomalous magnetic moment.