New molecular bonds existing in the strong interaction

TL;DR

This paper extends the hadronic covalent bond concept to explain new exotic hadrons like Zc(3900) and X(3872), emphasizing the role of shared quarks, sea quark-antiquark pairs, and the Pauli principle in strong interactions.

Contribution

It introduces an improved mechanism for hadronic bonds involving shared light quarks and antiquarks, accounting for creation and annihilation processes in strong interactions.

Findings

Explains Zc(3900) as a molecular state with shared light quark-antiquark pairs.

Highlights the importance of sea quark-antiquark pairs in hadronic bonding.

Proposes that creation and annihilation bonds are unique to strong interactions, aiding QCD confinement studies.

Abstract

Similar to the covalent bond in chemical molecules induced by shared electrons, we proposed in [Commun. Theor. Phys. 74 (2022) 125201] the hadronic covalent bond induced by shared light quarks to explain the $T_{cc}(3875)$ and the deuteron. In this paper we improve and extend this mechanism to explain the $Z_c(3900)$, which is bound by the shared light quark-antiquark pair along with sea quark-antiquark pairs from the vacuum. Our analysis is based on the following forward and backward reasoning: a hadronic molecule exists, iff the attraction between its components is strong enough, iff the wave functions of its components significantly overlap with each other, iff the Pauli principle is well satisfied among all the shared quarks and antiquarks. Additionally, the $X(3872)$ is so unique that we need to further consider the annihilation of the shared light quark-antiquark pair, just in line with the reasoning that the creation and annihilation of sea quark-antiquark pairs should be given equal consideration. Both the creation and annihilation molecular bonds exist only in the strong interaction, not in the electromagnetic interaction, and they provide a quasi-static low-energy platform for studying the QCD confinement.