Partial Breaking of N=2 Supersymmetry and Decoupling Limit of Nambu-Goldstone Fermion in U(N) Gauge Model

We study the N=1 U(N) gauge model obtained by spontaneous breaking of N=2 supersymmetry. The Fayet-Iliopoulos term included in the N=2 action does not appear in the action on the N=1 vacuum and the superpotential is modified to break discrete R symmetry. We take a limit in which the Kahler metric becomes flat and the superpotential preserves non-trivial form. The Nambu-Goldstone fermion is decoupled from other fields but the resulting action is still N=1 supersymmetric. It shows the origin of the fermionic shift symmetry in N=1 U(N) gauge theory.