Zooming in on Multiquark Hadrons within QCD Sum-Rule Approaches

TL;DR

This paper refines QCD sum-rule methods to distinguish genuine multiquark contributions from background effects, improving the theoretical understanding of exotic multiquark hadrons like tetraquarks.

Contribution

It introduces a clear classification of correlation function contributions, isolating multiquark-supporting terms for more accurate QCD sum-rule analyses.

Findings

Multiquark-phile contributions involve multiple gluon exchanges.

Non-multiquark contributions can be identified and discarded.

Enhanced criteria for studying exotic multiquark states.

Abstract

Aiming at self-consistent descriptions of multiquark hadrons (such as tetraquarks, pentaquarks, hexaquarks) by means of QCD sum rules, we note that the totality of contributions to two-point or three-point correlation functions that involve, respectively, either two or just a single operator capable of interpolating the particular multiquark under study can be straightforwardly disentangled into two disjoint classes defined by unambiguously identifiable members. The first is formed by so-called multiquark-phile contributions which indeed might support multiquarks. In the case of flavour-exotic tetraquarks, by definition composed of four (anti-) quarks of mutually different flavours, a tetraquark-phile contribution has to exhibit two or more gluon exchanges of appropriate topology. The second consists of contributions evidently not bearing any relation to multiquarks; these must be discarded when studying multiquarks by QCD sum rules. The first class only should enter the "multiquark-adequate" QCD sum rules for exotic hadrons.