They used to think that the inflaton (the field/particle system for inflation) was originally the Higgs Field, but as it turns out, the Higgs Field it isn't. They then thought it may have something to do with
GUT's, but the original theories for GUT's don't stack up so now they think it maybe something to do with
SUSY and
M Theory. What we do know is that when the symmetry was broken, the high energy, negative pressure false vacuum immediately collapsed into the low energy, positive pressure true vacuum via the nucleation of bubbles of true vacuum. These were essentially what turned out to be our universe.