Nankai Univ, Dept Phys, Tianjin 300071, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
; China Ctr Adv Sci & Technol, World Lab, Beijing 100080, Peoples R China
The properties of nuclear matter are discussed with the relativistic mean-field (RMF) theory. Then, we use two models in studying the in-medium properties of Theta(+): A pointlike Theta(+) in the usual RMF and a K pi N structure for the pentaquark. It is found that the in-medium properties of Theta(+) are dramatically modified by its internal structure. The effective mass of Theta(+) in medium is, at normal nuclear density, about 1030 MeV in the pointlike model, whereas it is about 1120 MeV in the K pi N pentaquark model. The nuclear potential depth of Theta(+) in the K pi N model is approximately -37.5 MeV, much shallower than -90 MeV in the usual pointlike RMF model.