On the mixing phase of isobaric analog resonances

Possible sources generating the mixing phase of an isobaric analog resonance are considered by means of the phenomenological theory of resonance reactions. For the case of direct mixing of overlapped doorway resonances, the large mixing phase can be produced only by the interference of internal coupling and coupling through a continuum of comparable strength. For the mixing of the resonance with the ocean of compound states, the mixing phase is known to be connected with the correlation between the spreading matrix elements of the resonance and those which couple background states to the continuum. Alternatively, we calculate the mixing phase due to the asymmetry of the resonance position with respect to the energy interval of background states. Using an approach associated with the estimates of the complexity of compound wave functions and a corresponding scaling of matrix elements, the reasons for the small variations in the spreading widths of the IAR are discussed. The consideration is of a general character and can be applied to any resonance reaction. (orig.)