Large $N$ Tensor and SYK Models

Abstract

The SYK model proposed by Sachdev, Ye, and Kitaev consists of Majorana fermions that interact randomly four at a time. The model develops a dense spectrum above the ground state, due to which the model becomes nearly conformal. This suggests that a holographic dual may exist, which makes the SYK model interesting in the study of quantum gravity. It has been found that the SYK model is similar to large $N$ tensor models: in both models, only the melonic diagrams survive in the large $N$ limit. In this thesis, we explore the large $N$ tensor model with $O(N)^3$ symmetry containing two flavors of Majorana fermions in the fundamental representation. Its quartic Hamiltonian depends on a real parameter $\beta$. We derive the kernels of the four point functions. With the spectra that we find from the kernels, we calculate the scaling dimensions of several types of conformal primaries. We also find a duality relation between two Hamiltonians of different values of $\beta$. This is not a perfect duality, because the normalization of energy scales with the transformation. Nevertheless, the ratios of the energies are the same, and the operator dimensions are preserved. In addition, we discover that for $\beta > 1$ or $\beta < 0$ the scaling dimensions of one of the conformal primaries become complex, rendering the model unstable.