The coupled N,N system is described by a K-matrix method. The parameters in this model are adjusted to get an optimal fit to N→N, N→N, and ␥N→N data in an energy range of about 100 MeV each side of the threshold. In the notation T Ϫ1 ϩiq ϭ1/aϩ ͑r 0 /2͒ q 2 ϩsq 4 , q being the momentum in the N center of mass, the resulting effective range parameters for N scattering are found to be a ͑fm͒ ϭ0.75͑4͒ϩi0.27 (3), r 0 ͑fm͒ ϭ-1.50͑13͒Ϫi0.24͑4͒, and s ͑fm 3 ) ϭ-0.10͑2͒Ϫi0.01͑1͒. ͓S0556-2813͑97͒50705-9͔ PACS number͑s͒: 13.75.Gx, 25.80.Ϫe, 25.40.VeThe pion-nucleon and pion-nucleus interactions have been much studied, both theoretically and experimentally, for many years. However, the corresponding interactions of the meson, mainly because of the lack of -beams, have-by comparison-been neglected. The main interest in 's has been the possibility of -nuclear quasibound states. Such states were first predicted by Haider and Liu ͓1͔ and Li et al.͓2͔, when it was realized that the -nucleon interaction was attractive. Calculations by Ueda indicated ͓3͔ that this may *Electronic

Using multiple scattering theory the scattering lengths of η mesons on helium nuclei are calculated and checked against final state η interactions from the pd → η 3 He and dd → η 4 He reactions. The existence of an η 4 He quasibound state is indicated.

The present status of the theory of nucleon resonances in nuclei is reviewed.A detailed account is given of the techniques used to generate these resonance configurations from the purely nucleonic configurations. Situations in two-and threenucleon systems in which the resonance configurations appear to play a role are discussed. Heavier nuclei are also mentioned. The effect of resonances in nuclear and neutron matter is also reviewed.