One-loop effects in supergravity models with an additional U(1)

For an Abelian extended Supergravity model, we investigate some important low energy parameters: tan�, Z − Zmixing angle, lightest CP-even Higgs mass bound, Zmass, and effective µ parameter. By integrating the RGE's from string scale down to the weak scale we constuct the scalar potential, and analyze the quantities above at the tree- and one-loop levels by including the contributions of top squarks and top quark in the effective potential. PACS: 04.65.+e, 12.60.Jv