PRE-BIG-BANG INFLATION REQUIRES FINE-TUNING

The pre-big-bang cosmology inspired by superstring theories has been s uggested as an alternative to slow-roll inflation. We analyze, in both the Jordan and Einstein frames, the effect of spatial curvature on th is scenario and show that too much curvature - of either sign - reduce s the duration of the inflationary era to such an extent that the flat ness and horizon problems are not solved. Hence, a fine-tuning of init ial conditions is required to obtain enough inflation to solve the cos mological problems. [S0556-2821(97)01020-5].