The recent measurement of the muon anomalous magnetic moment $a_{\mu }$ shows a $2.6\sigma$ deviation from the standard model value. We show that it puts an interesting bound on the mass of the second generation leptoquarks. To account for the data the leptoquark must have both left- and right-handed couplings to the muon. Assuming that the couplings have electromagnetic strength, the mass is restricted in the range 0.7 $\mathrm{TeV}<M_{\mathrm{LQ}}<2.2\mathrm{}\hspace{0.5em}\mathrm{TeV}\mathrm{}$ at 95% C.L. We also discuss constraints coming from other low energy and high energy experiments. If first-second-generation universality is assumed, constraints come from atomic-parity violation and charged-current universality. We show that the coexistence with other leptoquarks can satisfy these additional constraints and at the same time does not affect $a_{\mu }.$

• Received 21 February 2001

DOI:https://doi.org/10.1103/PhysRevD.64.033001