Many-body theory for simultaneous photoionization and photoexcitation of helium

Brueckner-Goldstone many-body perturbation theory is applied to study the simultaneous photoionization and photoexcitation (SSP) of helium. The results are used to examine the validity and limitations of other approaches to the problem. The oscillator strengths ($\text{d}\text{?}\text{?}$) for the transition 1s²→(2s ?p)¹P and 1s²→(2p ?s)¹P are compared with the results of Brown. The cross section for SPP at the photoexcitation threshold (65.399 eV) is found to be in agreement with the experimental result of Samson.