GUT inflation and proton decay after WMAP5 data

We employ Coleman-Weinberg and Higgs potentials to implement inflation in nonsupersymmetric grand unified theories (GUTs) such as SU(5) and SO(10). To realize a scalar spectral index close to 0.96, as indicated by the most recent WMAP 5-year analysis, the energy scale of observable inflation turns out to be of order 10(16) GeV. This implies a GUT symmetry breaking scale of similar magnitude and proton lifetime of order 10(34)-10(38) years. In some SO(10) models with axion dark matter, the scalar leptoquark boson exchange leads to proton decay with a lifetime of order 10(34)-10(35) years.