arXiv:hep-th/0506055v1 7 Jun 2005 Stable False Vacuum Mohammad R. Garousi and Kazem Bitaghsir Fadafan Department of Physics, Ferdowsi university, P.O. Box 1436, Mashhad, Iran Institute for Studies in Theoretical Physics and Mathematics IPM P.O. Box 19395-5531, Tehran, Iran ABSTRACT Recently a tachyon DBI action is proposed for describing the non-coincident D p -brane-anti- D p -brane system. For branes separation larger than √ 2π 2 α ′ , the tachyon potential has both false and true vacuums. We shall show that due to the non-standard form of the kinetic term in the effective action, the ”overshoot” argument of Coleman does not satisfy. This indicates that for p> 0, the vacuum tunneling from the false to the true vacuum occurs only when the branes separation is smaller than some critical value, and the false vacuum is stable otherwise. 0