It has been argued that supergravity models of inflation with vanishing sound speeds, c s , lead to an unbounded growth in the production rate of gravitinos. We consider several models of inflation to delineate the conditions for which c s = 0 . In models with unconstrained superfields, we argue that the mixing of the Goldstino and inflatino in a time-varying background prevents the uncontrolled production of the longitudinal modes. This conclusion is unchanged if there is a nilpotent field associated with supersymmetry breaking with constraint S 2 = 0 , i.e., (s)Goldstino-less models. Models with a second orthogonal constraint, S ( Φ ? Φ ˉ ) = 0 , where Φ is the inflaton superfield, which eliminates the inflatino, may suffer from the overproduction of gravitinos. However, we point out that these models may be problematic if this constraint originates from a UV Lagrangian, as this may require using higher derivative operators. These models may also exhibit other pathologies, such as c s > 1 , which are absent in theories with the single constraint or unconstrained fields.
展开▼
