Pion leptonic decays and supersymmetry

We compute supersymmetric contributions to pion leptonic (pil2) decays in the minimal supersymmetric standard model (MSSM). When R-parity is conserved, the largest contributions to the ratio Re/µ[equivalent]Gamma[pi+-->e+nue(gamma)]/Gamma[pi+-->µ+nuµ(gamma)] arise from one-loop (V-A)[direct-product](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 Re/µ while remaining consistent with all other precision observables.