David Wands

I give a general formulation of the constraints on models of inflation ended by a first order phase transition arising from the requirement that they do not produce too many large (observable) true vacuum voids -- the `big bubble problem'. It is shown that this constraint can be satisfied by a simple model in Einstein gravity -- a variant of `hybrid' or `false vacuum' inflation. The idea that inflation could be ended by a first order phase transition is often dismissed as too problematic following Guth's original trouble in finding a graceful exit from the false vacuum [1]. The scalar field, /, whose self-interaction potential acts like a cosmological constant driving the expansion, is trapped in a local potential minimum so cannot evolve classically. A fixed tunnelling rate to the true vacuum in a de Sitter universe leads to a time invariant state. One expects the phase transition to complete either at once or not at all. First order inflation was revived in the guise of extended infl..