Quantum critical behavior in three dimensional lattice Gross-Neveu models

We study quantum critical behavior in three dimensional lattice Gross-Neveu models containing two massless Dirac fermions. We focus on two models with SU(2) flavor symmetry and either a $Z_2$ or a U(1) chiral symmetry. Both models could not be studied earlier due to sign problems. We use the fermion bag approach which is free of sign problems and compute critical exponents at the phase transitions. We estimate $ u = 0.83(1)$, $eta = 0.62(1)$, $eta_psi = 0.38(1)$ in the $Z_2$ and $ u = 0.849(8)$, $eta = 0.633(8)$, $eta_psi = 0.373(3)$ in the U(1) model.