R-Symmetry and Gravitino Abundance

Supersymmetry breaking sectors generically have an approximate global U(1) $R$-symmetry. Thermal effects tend to restore the $R$-symmetry in the reheated early universe. We revisit the gravitino generation from the thermal plasma and we argue that an $R$-symmetric phase suppresses the gaugino masses and thereby the production of the helicity $\pm 1/2$ gravitino component. For reasonable values of the hidden sector parameters the gravitino can account for the dark matter of the universe with a relic abundance characterized by a remarkable insensitivity to the reheating temperature.