Exotics in the $\pi D$ system

TL;DR

This paper investigates exotic states in the $$ system, combining theoretical models and lattice QCD simulations to suggest some states are hadronic molecules rather than simple quark-antiquark pairs.

Contribution

It provides evidence from lattice QCD and chiral perturbation theory that certain exotic states are better described as multiquark or molecular states rather than traditional quark-antiquark mesons.

Findings

Identification of a $$ bound state in the flavor-sextet representation.

Observation of repulsion in the [15] representation consistent with Goldstone boson interactions.

Support for the molecular structure hypothesis of certain exotic states.

Abstract

In this proceedings we consider several states, namely the $D^*_{s0}(2317)$, $D_{s1}(2460)$, $D^*_{0}(2300)$ and $D_{1}(2430)$, which appear to defy description as simple quark-antiquark pairs. Theoretical input from unitarized chiral perturbation theory suggests they can be understood as emerging from Goldstone-Boson--$D$-meson scattering. We present results from an $SU(3)$ flavor-symmetric lattice QCD simulation at large pion masses suggesting that there exists a $\pi D$ bound state in the flavor-sextet representation that cannot emerge for quark-antiquark states, but that appears naturally from the multiquark states. Moreover, we find repulsion in the [15] representation, which establishes the pattern predicted for the interactions of Goldstone bosons with $D$ mesons. This suggests these states may have the structure of hadronic molecules.