Non-Commutativity of the Zero Chemical Potential Limit and the   Thermodynamic Limit in Finite Density Systems
  Monte Carlo simulations of finite density systems are often plagued by the complex action problem. We point out that there exists certain non-commutativity in the zero chemical potential limit and the thermodynamic limit when one tries to study such systems by reweighting techniques. This is demonstrated by explicit calculations in a Random Matrix Theory, which is thought to be a simple qualitative model for finite density QCD. The factorization method allows us to understand how the non-commutativity, which appears at the intermediate steps, cancels in the end results for physical observables. 
Jan Ambjorn (NBI and ITP Utrecht), Konstantinos N. Anagnostopoulos (U.   Crete and NTUA), Jun Nishimura (KEK) and Jacobus J....