Fermion bag solutions to some sign problems in four-fermion field theories

Understand

Lattice four-fermion models containing $N$ flavors of staggered fermions, that are invariant under $Z_2$ and U(1) chiral symmetries, are known to suffer from sign problems when formulated using the auxiliary field approach.

• Although these problems have been ignored in previous studies, they can be severe.
• In this talk, we show that the sign problems disappear when the models are formulated in the fermion bag approach, allowing us to solve them rigorously for the first time.