Spin Chains in N=2 Superconformal Theories: from the Z_2 Quiver to Superconformal QCD

TL;DR

This paper investigates the potential integrability of N=2 superconformal QCD by analyzing the one-loop dilation operator and spin-chain models, providing evidence that it may be integrable in the large N limit.

Contribution

It introduces a novel spin-chain model for N=2 superconformal QCD and explores its integrability properties through scattering and Yang-Baxter equation analysis.

Findings

The spin-chain Hamiltonian includes flavor dimer excitations.

The two-magnon S-matrix satisfies the Yang-Baxter equation at the orbifold point.

Evidence suggests one-loop integrability of planar N=2 superconformal QCD in the large N limit.

Abstract

In this paper we find preliminary evidence that N=2 superconformal QCD, the SU(N_c) SYM theory with N_f= 2 N_c fundamental hypermultiplets, might be integrable in the large N Veneziano limit. We evaluate the one-loop dilation operator in the scalar sector of the N=2 superconformal quiver with SU(N_c) X SU(N_{\check c}) gauge group, for N_c = N_{\check c}. Both gauge couplings g and \check g are exactly marginal. This theory interpolates between the Z_2 orbifold of N=4 SYM, which corresponds to \check g=g, and N=2 superconformal QCD, which is obtained for \check g -> 0. The planar one-loop dilation operator takes the form of a nearest-neighbor spin-chain Hamiltonian. For superconformal QCD the spin chain is of novel form: besides the color-adjoint fields \phi^a_{b}, which occupy individual sites of the chain, there are "dimers" Q^a_{i} \bar Q^i_{b} of flavor-contracted fundamental fields, which occupy two neighboring sites. We solve the two-body scattering problem of magnon excitations and study the spectrum of bound states, for general \check g/g. The dimeric excitations of superconformal QCD are seen to arise smoothly for \check g -> 0 as the limit of bound wavefunctions of the interpolating theory. Finally we check the Yang-Baxter equation for the two-magnon S-matrix. It holds as expected at the orbifold point \check g = g. While violated for general \check g \neq g, it holds again in the limit \check g -> 0, hinting at one-loop integrability of planar N=2 superconformal QCD.