Pauli-Villars regularization
In theoretical physics, the Pauli-Villars regularization is a particular procedure to get rid of infinities in divergent integrals that correspond to Feynman diagrams. It was devised by Wolfgang Pauli and Felix Villars in 1949.
In this treatment, a divergence arising from loop effects of a particle is cancelled by the opposite divergence induced by a very heavy fictitious particle with negative norm. When the mass of the fictitious particle is sent to infinity, one expects that the effects of the fictitious particle disappear.
This regulator isn't gauge invariant.