Oscillons: Resonant configurations during bubble collapse

Oscillons are localized, nonsingular, time-dependent, spherically symmetric solutions of nonlinear scalar field theories which, although unstable, are extremely long lived. We show that they naturally appear during the collapse of subcritical bubbles in models with symmetric and asymmetric double-well potentials. By a combination of analytical and numerical work we explain several of their properties, including the conditions for their existence, their longevity, and their final demise. We discuss several contexts in which we expect oscillons to be relevant. In particular, their nucleation during cosmological phase transitions may have wide-ranging consequences.