Correction exponents in the chiral Heisenberg model at 1/N²: singular contributions and operator mixing

We calculate the correction exponents in the chiral Heisenberg model in the 1/ N expansion. These exponents are related to the slopes of β β functions at the phase transition point. We present the results at order 1/N² 1 / N 2 and check that they agree with the results of the ε ϵ expansion near $$d = 4$$ d = 4 . We find that one of the correction exponents diverges as d → 3 d → 3 . We argue that the appearance of the pole is a rather general phenomenon and is associated with operator mixing involving the system of four-fermion operators. After analyzing the operator mixing structure, we propose a resummation procedure which modifies the exponents already at leading order . We also perform calculations directly in the three-dimensional model and find complete agreement with the resummed exponents.