Tetraquarks made of sufficiently unequal-mass heavy quarks are bound in QCD

TL;DR

This study demonstrates that tetraquarks with sufficiently unequal heavy quark masses are bound states in QCD, providing critical mass ratios and detailed structural insights using advanced computational methods.

Contribution

It is the first to show bound tetraquarks occur only with sufficiently unequal heavy quark masses, using variational and Green's function Monte Carlo methods in potential nonrelativistic QCD.

Findings

Bound tetraquarks exist for large enough mass ratios.

No bound states for equal-mass quark-antiquark pairs.

Predicted critical mass ratios for binding.

Abstract

Tetraquarks, bound states composed of two quarks and two antiquarks, have been the subject of intense study but are challenging to understand from first principles. We apply variational and Green's function Monte Carlo methods to compute tetraquark ground-state energies in potential nonrelativistic QCD using a wide range of color and spatial wavefunctions. We find no evidence for bound tetraquarks composed of equal-mass quarks and antiquarks. Conversely, we find clear evidence for the existence of bound tetraquarks for sufficiently unequal quark/antiquark mass ratios at all overall mass scales where our effective theory results are applicable. We predict the critical mass ratios for bound state formation and study tetraquark bound states' spatial and color structure at leading order and next-to-leading order in potential nonrelativistic QCD.