Mass hierarchy and localization of gravity in extra time

We consider Randall-Sundrum model with localized gravity, replacing the ext ra compact space-like dimension by a time-like one. In this way the solutio n to the hierarchy problem can be reconciled with a correct cosmological ex pansion of the visible universe, just as a trivial result of the sign flip of cosmological constants in the bulk and on the 3-branes relative to the c ase of extra space-like dimension. Some phenomenological aspects of the pro posed scenario related to the tachyonic nature of Kaluza-Klein states of gr aviton are also discussed. (C) 2000 Published by Elsevier Science B.V.