EPS-HEP2019

Flavor-exotic tetraquarks in large-Nc QCD: do they exist?

13 Jul 2019, 10:45

15m

ICC - Baekeland 1 (Ghent)

Parallel talk QCD and Hadronic Physics QCD and Hadronic Physics

Speaker

Dmitri Melikhov (HEPHY)

Description

A salient feature shared by all tetraquark candidates observed in experiment is the absence of flavor-exotic states of the type $\overline{a}b\overline{c}d$, with four different quark flavors.This phenomenon may be understood from the properties of large-Nc QCD: On the one hand, previous work shows that consistency conditions for flavor-exotic Green functions, potentially containing these tetraquark poles, require the existence of two tetraquarks $T_A$ and $T_B$: each of them should decay dominantly via a single two-meson channel, $T_A\to M_{ab}{M}_{cd}$ and $T_B\to M_{ad}{M}_{cb}$. On the other hand, we have at hand only one diquark-antidiquark flavor structure $(\overline{a}\overline{c})(bd)$ that might produce a compact tetraquark bound state. Taking into account that the diquark-antidiquark structure is the only viable candidate for a compact tetraquark state, one concludes that it is impossible to obtain two different narrow tetraquarks decaying dominantly into distinct two-meson channels. This contradiction suggests that large-$N_c$ QCD does not support the existence of narrow flavor-exotic tetraquarks. This argument does not rule out the possible existence of broad molecular-type flavor-exotic states, or of molecular-type bound states lying very close to the two-meson thresholds.

Presentation materials

Melikhov_Exotic.pdf