Normalizing flows for the real-time sign problem

Understand

We discuss the application of normalizing flows to bosonic lattice field theories with real-time sign problems.

• A normalizing flow, once it is found for such a lattice field theory, is guaranteed to solve its sign problem.
• We argue for the existence of normalizing flows for bosonic lattice field theories in the Schwinger-Keldish formalism in a few ways.
• We then discuss how this existence is a specific feature of bosonic theories: such arguments break down for fermionic systems, whether at finite density or in real-time.