Beyond the Conventional Quark Model: Using QCD Sum Rules to Explore the Spectrum of Exotic Hadrons

Abstract

Exotic hadrons are theoretical structures allowed by our current understanding of Quantum Chromodynamics (QCD), lying outside the traditional $q\bar{q}$, $qqq$, or $\bar{q}\bar{q}\bar{q}$ understanding of mesons and baryons. These exotic hadrons potentially give us a unique window into the properties of the gluon, the nature of color confinement, and the strong interaction. As we progress through the precision-era of particle physics and experiments such as BESIII, Belle, BaBar, LHCb, GlueX, and PANDA amass experimental data across the expected mass ranges of exotic hadrons (such as hybrid mesons with both $\bar{q}q$ quark content and a gluonic component), theoretical predictions of the individual mass states and the overall multiplet structure are crucial in identifying exotic states as well as departures from predicted behaviour. Using the methodology of QCD sum-rules (QCDSRs), we explore the properties of exotic hadrons, and discuss the QCDSR methodology and its extensions