Pion leptonic decays and supersymmetry

We compute supersymmetric contributions to pion leptonic (${\pi }_{l2}$) decays in the minimal supersymmetric standard model (MSSM). When R-parity is conserved, the largest contributions to the ratio $R_{e/\mu }\equiv \Gamma [{\pi }^{+}\to e^{+}{\nu }_e(\gamma )]/\Gamma [{\pi }^{+}\to {\mu }^{+}{\nu }_{\mu }(\gamma )]$ arise from one-loop $(V-A)\otimes (V-A)$ corrections. These contributions can be potentially as large as the sensitivities of upcoming experiments; if measured, they would imply significant bounds on the chargino and slepton sectors complementary to current collider limits. We also analyze R-parity-violating interactions, which may produce a detectable deviation in $R_{e/\mu }$ while remaining consistent with all other precision observables.