Origin of the N1 (1150) enhancement and the d1(2200) effect

Using pion exchange and Δ(1236) excitation inside the deuteron, the N¹(1150) enhancement with isospin $\text{I =}\text{1}\text{2}$, seen in evidence in dp coherent interactions, is explained. Good agreement is obtained, without any arbitrary normalization, between the Frascati-Caen-Saclay data and the predictions of this model. Its leading features and applications to other experiments are given.