Why static bound-state calculations of tetraquarks should be met with scepticism

Abstract：

Recent experimental signals have led to a revival of tetraquarks, the hypothetical q²q² hadronic states proposed by Jaffe in 1976 to explain the light scalar mesons. Mesonic structures with exotic quantum numbers have indeed been observed recently, though a controversy persists as to whether these are true resonances and not merely kinematical threshold enhancements, or otherwise states not of a true q²q² nature. Moreover, puzzling non-exotic mesons are also often claimed to have a tetraquark configuration. However, the corresponding model calculations are practically always carried out in pure and static bound-state approaches, ignoring completely the coupling to asymptotic two-meson states and unitarity, especially the dynamical effects thereof. In this short paper we argue that these static predictions of real tetraquark masses are highly unreliable and provide little evidence of the very existence of such states.