Inflation in no-scale supergravity

$R+{R}^{2}$ supergravity is known to be equivalent to standard supergravity coupled to two chiral supermultiples with a no-scale K\"ahler potential. Within this framework, that can accommodate vanishing vacuum energy and spontaneous supersymmetry breaking, we consider modifications of the associated superpotential and study the resulting models, which, viewed as generalizations of the Starobinsky model, for a range of the superpotential parameters, describe viable single-field slow-roll inflation. In all models studied in this work, the tensor-to-scalar ratio is found to be small, well below the upper bound established by the very recent PLANCK and BICEP2 data.