Abstract
The diquark is a strongly correlated quark pair that plays an important role in hadrons and hadronic matter. In order to treat the diquak as a building block of hadrons, we formulate an effective theory of diquark fields with $SU(3)_R \times SU(3)_L$ chiral symmetry. We concentrate on the scalar ($0^+$) and pseudoscalar ($0^-$) diquarks and construct a linear-sigma-model Lagrangian. It is found that the effective Lagrangian contains a new type of chirally symmetric meson-diquark-diquark coupling that breaks axial $U_A(1)$ symmetry. We discuss consequences of the $U_A(1)$ anomaly term to the diquark masses as well as to the singly heavy baryon spectrum, which is directly related to the diquark spectrum. We find an inverse mass ordering between strange and nonstrange diquarks. The parameters of the effective theory can be determined by the help of lattice QCD calculations of diquarks and also from the mass spectrum of the singly heavy baryons. We determine the strength of the $U_A(1)$ anomaly term, which is found to give a significant portion of the diquark masses.
Highlights
Recent developments of hadron spectroscopy has brought a completely new picture of hadrons
We determine the strength of the UAð1Þ anomaly term, which is found to give a significant portion of the diquark masses
We have proposed a chiral effective theory of scalar and pseudoscalar diquarks
Summary
Recent developments of hadron spectroscopy has brought a completely new picture of hadrons. Effective theories of diquarks were explored in the context of color superconductivity at high density QCD [20,21], where it is shown that the axial UAð1Þ anomaly plays an important role [22,23]. We propose a chiral effective theory of scalar and pseudoscalar diquarks, based on linear representations of SUð3ÞR × SUð3ÞL symmetry. Such an effective theory may be applied, once the parameters are determined by the known experimental data, to the heavy baryon systems, and to tetraquarks, and the other multiquark hadrons.
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