Spin-fermion model near the quantum critical point: one-loop renormalization group results

We consider spin and electronic properties of itinerant electron systems, described by the spin-fermion model, near the antiferromagnetic critical point. We expand in the inverse number of hot spots in the Brillouin zone, N and present the results beyond previously studied $N = \infty $ limit. We found two new effects: (i) Fermi surface becomes nested at hot spots, and (ii) vertex corrections give rise to anomalous spin dynamics and change the dynamical critical exponent from z=2 to z>2. To first order in 1/N we found $z = 2N/(N-2)$ which for a physical N=8 yields $z\approx 2.67$.