Correlations in non-Hermitian systems and diagram techniques for the steady state

Abstract

I construct a diagrammatic technique for non-Hermitian fermionic systems which allows addressing correlation effects in the steady state by systematic expansion. Applying this method to exceptional points or rings, I find that nodal objects in non-Hermitian systems are generically displaced in momentum-space due to interactions. This is a consequence of the fact that exceptional points invariably break a class of orthonormal symmetries that are generally present for nodal points in Hermitian systems and which protect the integrity of the node at low energy scales.