Scattering of mesons and emergence of tetraquarks in two-dimensional QCD

TL;DR

This paper investigates meson scattering in two-dimensional QCD with multiple flavors, revealing that unitarized scattering amplitudes produce a tetraquark bound state near the two-meson threshold.

Contribution

It demonstrates how a tetraquark state emerges from meson scattering in 2D QCD through unitarization of coupled-channel amplitudes.

Findings

Finiteness of scattering amplitudes at order N_c^{-2}

Emergence of a tetraquark bound state near the elastic threshold

Effective meson interaction via quark-exchange contact term

Abstract

Scattering of two mesons is considered in the framework of two-dimensional QCD in the large-$N_c^{}$ limit with four different quark flavors. The scattering takes place through two coupled channels, corresponding to direct and quark-exchange processes, which are of order $O(N_c^{-2})$ and $O(N_c^{-1})$, respectively. Finiteness of the scattering amplitudes to order $N_c^{-2}$ is pointed out. The theory reduces, at low energies, to an effective theory of mesons, interacting by a quark-exchange process, by means of a contact term. The unitarization of the scattering amplitudes leads to the emergence of a tetraquark bound state, located very close to the lowest two-meson elastic threshold.