Coupled channel approach for pionic atoms 1H and 3He

The momentum-space method by Vincent and Phatak is extended to deal with a two-particle bound state, coupled to other open channels. The present approach is applied to two systems of coupled channels represented by π-p, π0n, γn and π-3He, π03H, γ3H, respectively. The energy shifts and absorption widths of the 1s levels of pionic hydrogen and the 3He π-atom are calculated and compared with existing experimental data. (orig.)