# The Tetraquark Candidate Zc(3900) from Dynamical Lattice QCD Simulations

## TL;DR

This study uses lattice QCD simulations to analyze the structure of the Zc(3900) tetraquark candidate, concluding it is a threshold cusp rather than a conventional resonance based on coupled-channel scattering data.

## Contribution

The paper provides the first lattice QCD analysis of the Zc(3900) structure, revealing it as a threshold cusp instead of a resonance, using dynamical simulations and coupled-channel scattering.

## Key findings

- Zc(3900) is a threshold cusp, not a conventional resonance.
- Interactions are dominated by off-diagonal couplings.
- Lattice QCD simulations support the cusp interpretation.

## Abstract

The structure of the tetraquark candidate $Z_{c}(3900)$, which was experimentally reported in $e^+ e^-$ collisions, is studied by the s-wave meson-meson coupled-channel scattering on the lattice. The s-wave interactions among the $\pi J/\psi$, $\rho \eta_{c}$ and $D \bar{D}^{*}$ channels are derived from (2+1)-flavor dynamical QCD simulations at $m_{\pi}=410$--$700$ MeV. It is found that the interactions are dominated by the off-diagonal $\pi J/\psi$-$D \bar{D}^{*}$ and $\rho \eta_{c}$-$D \bar{D}^{*}$ couplings. With the interactions obtained, the s-wave two-body amplitudes and the pole position in the $\pi J/\psi$-$\rho \eta_{c}$-$D \bar{D}^{*}$ coupled-channel scattering are calculated. The results show that the $Z_{c}(3900)$ is not a conventional resonance but a threshold cusp. A semiphenomenological analysis with the coupled-channel interaction to the experimentally observed decay mode is also presented to confirm the conclusion.