  Minimal supersymmetric hybrid inflation utilizes a canonical Kahler potential
and a renormalizable superpotential which is uniquely determined by imposing a
U(1) R-symmetry. In computing the scalar spectral index $n_s$ we take into
account modifications of the tree level potential caused by radiative and
supergravity corrections, as well as contributions from the soft supersymmetry
breaking terms with a negative soft mass-squared term allowed for the inflaton.
All of these contributions play a role in realizing $n_s$ values in the range
0.96-0.97 preferred by WMAP. The U(1) R-symmetry plays an important role in
flipped SU(5) by eliminating the troublesome dimension five proton decay. The
proton decays into $e^+ \pi^0$ via dimension six operators arising from the
exchange of superheavy gauge bosons with a lifetime of order
$10^{34}$-$10^{36}$ years.
