We study the qualitative behavior of nonlinear Dirac equations arising in quantum field theory on complete Riemannian manifolds. In particular, we derive monotonicity formulas and Liouville theorems for solutions of these equations. Finally, we extend our analysis to Diracharmonic maps with curvature term.(2) The Thirring model [28] describes the self-interaction of fermions in two-dimensional Minkowski space:The Nambu-Jona-Lasinio model [25] is a model for interacting fermions with chiral symmetry. It also contains a quartic interaction term and is defined on an even-dimensional spacetime:Note that this model does not have a term proportional to |ψ| 2 in the energy functional.