The QCD sign problem as a total derivative

Understand

We consider the distribution of the complex phase of the fermion determinant in QCD at nonzero chemical potential and examine the physical conditions under which the distribution takes a Gaussian form.

• We then calculate the baryon number as a function of the complex phase of the fermion determinant and show 1) that the exponential cancellations produced by the sign problem take the form of total derivatives 2) that the full baryon number is orthogonal to this noise.
• These insights allow us to define a self-consistency requirement for measurements of the baryon number in lattice simulations.