Gravitational instantons and the branching off of the expanding universe
Rubakov V. A. , Tinyakov P. G.
A model of a gravitational field which interacts with the fields of matter was used to find the instanton which describes the branching off from a flat universe of a little, closed universe which subsequently expands classically under inflationary conditions. The existence of such instantons raises the possibility of self-nucleation of systems of expanding universes.