Unitarity Bounds on the Massive Spin-2 Particle Explanation of Muon $g-2$ Anomaly

TL;DR

This paper explores the unitarity constraints on a theoretical model where a massive spin-2 particle explains the muon g-2 anomaly, providing bounds on the particle's couplings based on high-energy scattering amplitudes.

Contribution

It derives unitarity bounds for a massive spin-2 particle model addressing the muon g-2 discrepancy, offering analytic constraints on couplings.

Findings

Derived unitarity bounds on spin-2 particle couplings.

Constrained parameter space for muon g-2 explanation.

Provided high-energy scattering amplitude calculations.

Abstract

Motivated by the long-standing discrepancy between the Standard Model prediction and the experimental measurement of the muon magnetic dipole moment, we have recently proposed to interpret this muon $g-2$ anomaly in terms of the loop effect induced by a new massive spin-2 field $G$. In the present paper, we investigate the unitarity bounds on this scenario. We calculate the $s$-wave projected amplitudes for two-body elastic scatterings of charged leptons and photons mediated by $G$ at high energies for all possible initial and final helicity states. By imposing the condition of the perturbative unitarity, we obtain the analytic constraints on the charged-lepton-$G$ and photon-$G$ couplings. We then apply our results to constrain the parameter space relevant to the explanation of the muon $g-2$ anomaly.