Controlling the Sign Problem in Finite Density Quantum Field Theory

Understand

Quantum field theories at finite matter densities generically possess a partition function that is exponentially suppressed with the volume compared to that of the phase quenched analogue.

• The smallness arises from an almost uniform distribution for the phase of the fermion determinant.
• Large cancellations upon integration is the origin of a poor signal to noise ratio.
• We study three alternatives for this integration: the Gaussian approximation, the "telegraphic" approximation, and a novel expansion in terms of theory-dependent moments and universal coefficients.