Proton-Neutron Mass Difference in a Unified Gauge Model of Leptons and Hadrons

We discuss some problems associated with the physical interpretation and the renormalization of the model devised by Weinberg which combines the SU (2) (1) gauge theory of leptons and the model. Some of the problems we discuss are: (1) renormalization counterterms of this model, (2) complications due to the existence of two scalar multiplets which develop vacuum expectation values, (3) the proton-neutron mass difference in this model. We point out that in this model there is a "zeroth-order" relation connecting the proton-neutron mass difference and certain coupling constants. Departure from this relation in higher orders is computable and we discuss the one-loop correction to this relation.