Absence of sign problem in the (saddle point approximation of the) nilpotency expansion of QCD at finite chemical potential

Understand

We have developed a method to derive the (approximate) quark contribution to the fermion free energy of QCD on a lattice, at finite temperature and chemical potential, with Kogut-Susskind fermions in the flavor basis.

• We show here the expression at zero temperature.
• This result has been obtained at the lowest order of the nilpotency expansion.
• At this order the well known "sign problem" does not arise and the quark contribution to the action can be used as a statistical weight in the Monte Carlo simulations.