AXINO MASS IN SUPERGRAVITY MODELS

We analyze the mass of the axino, the fermionic superpartner of the ax ion, in general supergravity models incorporating a Peccei-Quinn symme try and determine the cosmological constraints on this mass. In partic ular, we derive a simple criterion to identify models with an LSP axin o which has a mass of O(m(3/2)(2)/f(PQ)) = O(keV) and can serve as a c andidate for (warm) dark matter. We point out that such models have ve ry special properties and in addition, the small axino mass has to be protected against radiative corrections by demanding small couplings i n the Peccei-Quinn sector. Generically, we find an axino mass of order m(3/2). Such masses are constrained by the requirement of an axino de cay which occurs before the decoupling of the ordinary LSP. Especially , for a large Peccei-Quinn scale f(PQ) > 10(11) GeV this constraint mi ght be difficult to fulfill.