Theory HEP Seminar

Real-Time Vacuum Decay: From the Lattice to the Lab

Jonathan Braden

CITA

Quantum decay of false vacuum states via the nucleation of bubbles may have played an important role in the early history of our Universe. For example, in multiverse models based on false vacuum eternal inflation, the Big Bang of our observable Universe corresponds to one of these bubble nucleation events. Further, our observable Universe may have undergone a series of symmetry-breaking first-order phase transitions as it cooled, which may have produced a remnant background of gravitational waves.

I will present results from a real-time picture of false vacuum decay which, in contrast to existing semiclassical techniques, does not rely on classically forbidden tunneling paths. Some novel applications of this technique include computing bubble-bubble correlations, and decays from non-vacuum and non-thermal initial states. Lattice simulations are used to evolve initial realizations of fluctuations around the false vacuum forward in time via the classical equations of motion. In these simulations, we observe the false vacuum decay via the formation and subsequent expansion and coalescence of true vacuum bubbles. By sampling initial field realizations, we build up ensembles of these decay histories and empirically determine the bubble nucleation rate. I will also show how renormalisation effects manifest in these numerical simulations, which must be accounted for in quantitative comparisons to other approaches to vacuum decay. In particular, I will show that corrections to the effective mass of the field can have important impacts on the decay rate inferred from the standard Euclidean formalism.

Finally, I will discuss the possibility to emulate relativistic false vacuum decay in the lab using a two component dilute gas Bose-Einstein condensate (BEC). Under suitable experimental conditions, the relative phase of the two condensates behaves as an effective relativistic scalar field with periodic potential. Through an appropriate tuning of experimental parameters, a potential with a false vacuum minimum for this effective scalar can be created. This allows for the exciting prospect to experimentally observe relativistic false vacuum decay. Further, it opens up the possibility for an experimental test of the various theoretical approaches to vacuum decay.