We examine, in the context of certain string compactifications resulting in
five dimensional brane worlds the mechanisms of (self) tuning of the
cosmological constant and the recovery of standard cosmological evolution. We
show that self tuning can occur only as long as supersymmetry is unbroken
(unless additional assumptions are made) and that the adjustment of the
cosmological constant to zero after supersymmetry breaking and the recovery of
standard evolution are the same problem verifying previously made statements in
the context of general i.e. not necessarily string theoretic brane worlds. We
emphasize, however, that contrary to general brane worlds where the above
adjustment requires a fine tuning, stringy brane worlds contain an additional
integration constant due to the presence of the compact space thus allowing the
adjustment to be done only with integration constants.Comment: Talk given at the "M-theory Cosmology" conference in Cambridge,
England and at various other place
