Grand Unified Inflation Confronts WMAP

In a class of realistic four and five dimensional supersymmetric grand unified models, the scalar spectral index is found to be $n_s=0.98 (\pm 0.01)$, in excellent agreement with the values determined by several previous experiments and most recently by the Wilkinson Microwave Anisotropy Probe (WMAP). The models predict $dn_s/d{\rm ln}k\sim 10^{-3}$ and a negligible tensor-to-scalar ratio $r\sim 10^{-8}$. A new five dimensional supersymmetric SO(10) model along these is presented in which inflation is associated with the breaking of SO(10) to SU(5) at scale $M$, with $\delta T/T\propto (M/M_{\rm Planck})^2$, so that $M\simeq 10^{16}$ GeV. The inflaton decay leads to the observed baryon asymmetry via leptogenesis. We also discuss how the monopole problem is solved without the use of non-renormalizable terms.