Circular loops of string and spherical domain-wall bubbles of radius equal to the horizon can spontaneously nucleate in de Sitter space. These objects are expanded by the subsequent inflation, and by the end of the inflationary era they have a spectrum of sizes extending well beyond the present Hubble length. Monopole-antimonopole pairs with an initial separation equal to the horizon can also be produced. The cosmological implications of these effects are briefly discussed.

• Received 18 March 1991

DOI:https://doi.org/10.1103/PhysRevD.44.340