Multi-flavor massless QED$_2$ at finite densities via Lefschetz thimbles
  We consider multi-flavor massless $(1+1)$-dimensional QED with chemical potentials at finite spatial length and the zero-temperature limit. Its sign problem is solved using the mean-field calculation with complex saddle points. 
Yuya Tanizaki and Motoi Tachibana
hep-th hep-lat