An inflationary model which satisfies constraints from particle physics and cosmology is presented. The key feature is an SU(5)-singlet field which drives inflation, leads to proper density fluctuations, and solves the strong $\mathrm{CP}$ problem by the invisible axion mechanism. Thus, for the first time, all reservations about the inflationary universe are removed.

• Received 10 February 1984

DOI:https://doi.org/10.1103/PhysRevLett.52.1725