Solving the gravitino problem by the axino

In a large class of supersymmetric (SUSY) axion models the mass of the axino a (a fermionic superpartner of the axion) is predicted as m((a) over tilde) less than or similar to O(1) keV. Thus, the axino is the lightest SUSY particle (LSP). We pointed out that such a light axino provides a natural solution to the gravitino problem, if the gravitino is the next LSP. We derive a constraint on the reheating temperature T-R of inflation, T-R less than or similar to 10(15) GeV for the gravitino mass m(3/2) similar or equal to 100 GeV, which is much weaker than that obtained in the minimal SUSY standard model. (C) 2000 Published by Elsevier Science B.V.