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 gβ2 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 gβ2 anomaly.Comment: 23 pages, 7 figure