Implications of a Class of Grand-Unified Theories for Large-Scale Structure in the Universe

We consider a class of grand-unified theories in which cosmologically significant axion and neutrino energy densities arise naturally. To obtain large-scale structure we consider (1) an inflationary scenario, (2) inflation followed by string production, and (3) a noninflationary scenario with density fluctuations caused solely by strings. We show that inflation may be compatible with the recent observational indications that $\Omega <1\mathrm{}$ on the scale of superclusters, particularly if strings are present.