Hadronic Spectrum in the Chiral Large $N_c$ Extension of Quantum Chromodynamics

TL;DR

This paper explores the hadronic spectrum in a specialized large $N_c$ limit of QCD with unique fermion content, analyzing mass scaling, scattering amplitudes, and novel baryonium states.

Contribution

It introduces a new large $N_c$ extension of QCD with specific fermion representations and studies its hadronic spectrum, mass scaling, and unique non-trivial processes.

Findings

All hadron masses scale as ~N_c^0 n_q

Scattering amplitudes scale similarly to the lightest hadron mass

Identification of novel baryonium states and their decay processes

Abstract

We study Quantum Chromodynamics in the chiral large $N_c$ limit which contains a left-handed Weyl fermion in the fundamental representation, a left-handed Weyl fermion in the two index antisymmetric representation and $(N_c-3)$ left-handed Weyl fermions in the antifundamental representation of the $SU(N_c)$ gauge group. We construct gauge singlet composite operators and study their masses and correlation functions at large $N_c$. It is shown that all hadron masses scale as $\sim N_c^0 n_q$ where $n_q$ is the number of constituent quarks in the hadron. In addition by simple gluon exchange considerations it is seen that scattering amplitudes between hadrons have the same $N_c$ scaling as the mass of the lightest hadron involved. This is the case provided the hadrons in the scattering amplitude share a sufficiently large number of constituent quarks. The chiral large $N_c$ extension also allows for other non-trivial processes. For instance we consider two different baryonium states that are unique to this extension and that decay via emissions of two- and three-quark hadrons. Also other non-trivial scattering processes are considered. Finally, we study composites made of a mix of left- and right-handed fields. We categorize multiple groups of hadrons within the full spectrum according to their flavor structure. Within these groups all $n$-point functions scale the same.