Space-Time Duality and Vacuum Energy

The concept of Euclidean time is proposed which is dual to the usual Minkowski time. The De Sitter solution is shown to be dual to the anti-De Sitter solution under the dual transformation in which Euclidean time and Minkowski time are interchanged. This observation enables us to make a proposal in which supersymmetry is broken, but the four dimensional cosmological constant remains zero. An explicit model is proposed in which we calculate the cosmological constant. The phenomenology based on this model is presented, including the issue of the quark-lepton-Higgs mass matrix.