Exotic QQ\qbar\qbar States in QCD

TL;DR

This paper demonstrates that QCD predicts stable four-quark states involving heavy and light quarks, with potential for weakly bound meson molecules, especially in the bottom quark sector, due to pion exchange forces.

Contribution

It introduces the existence of stable four-quark QQ extbar q extbar q states in the heavy quark limit, highlighting the role of pion exchange in their binding.

Findings

Stable four-quark states predicted in QCD with heavy quarks.

Long-range pion exchange can bind two mesons into a weakly bound state.

Potential for observable bound states in the bottom quark sector.

Abstract

We show that QCD contains stable four-quark QQ\qbar\qbar hadronic states in the limit where the heavy quark mass goes to infinity. (Here Q denotes a heavy quark, \qbar a light antiquark and the stability refers only to the strong interactions.) The long range binding potential is due to one pion exchange between ground state Q\qbar mesons, and is computed using chiral perturbation theory. For the Q=b, this long range potential may be sufficiently attractive to produce a weakly bound two meson state.