SYK model with quadratic perturbations: the route to a non-Fermi-liquid

A. V. Lunkin, K. S. Tikhonov, M. V. Feigel'man

We study the stability of the SYK${}_4$ model with a large but finite number of fermions $N$ with respect to a perturbation, quadratic in fermionic operators. We develop analytic per…