Explicit CP violation in the Higgs sector of the next-to-minimal supersymmetric standard model

We analyze explicit CP violation in the Higgs sector of the next-to-minimal supersymmetric standard model which contains an additional gauge singlet held N. It is shown that there is no mixing among scalar and pseudoscalar Higgs fields in the two Higgs doublets, and scalar-pseudoscalar mixings could exist between two Higgs doublets and the singlet N, and between N itself. CP symmetry is conserved in the extreme limits [N] >> v, [N] << v and tan beta >> 1. In the region [N] = O(v) and tan beta = O(1), large scalar-pseudoscalar mixings are realized, and this effect can reduce the lightest Higgs mass. The mass difference between the no mixing and mixing cases is about 10 similar to 30 GeV. The neutron electric dipole moment in this model is consistent with the present experimental upper limit, provided that squark and gaugino masses are sufficiently heavy (O(1) TeV).