A detailed analysis is made of the pion photoproduction and pion radiative-capture data in the first resonance region in terms of a simple model incorporating $C$-violating and isotensor effects. An excellent fit is obtained, and the data can only be understood in the presence of the exotic terms. The stability of the parameters representing these effects is investigated against detailed variations in the model and against possible ambiguities in the proton data. The parameters specifying the ratio of isotensor to isovector resonance excitation ($t$) and the $T$-violating phase on neutrons ${\phi }_n$ are found to be stable, and have the values $t\sim -0.28\mathrm{}$ and ${\phi }_n\sim -{11}^{\circ }$. The consequences of this on other processes are briefly summarized, and found to be compatible with the present information. A discussion of the model-independent aspects of these questions is also given, including a critical review of other work known to the authors. Conventional models, i.e., those without exotic terms, are demonstrated to be incapable of describing the present data without violating more fundamental requirements. The particular exotic terms needed depend to some extent on the model; however, this dependence can be eliminated by improved data.

• Received 30 July 1971

DOI:https://doi.org/10.1103/PhysRevD.5.1117