Ordinary and radiative muon capture on the proton and the pseudoscalar form factor of the nucleon

We calculate ordinary and radiative muon capture on the proton in an effective field theory of pions, nucleons and delta isobars. We work to second order in the small scale expansion. To this order, ordinary muon capture is not affected by the delta. We demonstrate that the isobar effects on the photon spectrum and total rate in radiative muon capture are of the order of a few percent, consistent with earlier findings in a more phenomenological approach. We also discuss the induced pseudoscalar form factor of the nucleon and comment on the existing discrepancy between the TRIUMF data and the theoretical calculations