The quark model was formulated in 1964 to classify mesons as bound states made of a
quark–antiquark pair, and baryons as bound states made of three quarks. For a long time all …

A large number of experimental discoveries especially in the heavy quarkonium sector that
did not meet the expectations of the until then very successful quark model led to a …

In the past decade many charmonium-like states were observed experimentally. Especially
those charged charmonium-like Z c states and bottomonium-like Z b states cannot be …

Multiquark resonances are undoubtedly experimentally observed. The number of states and
the amount of details on their properties have been growing over the years. It is very recent …

Many efforts have been made to reveal the nature of the overabundant resonant structures
observed by the worldwide experiments in the last two decades. Hadronic molecules attract …

Chiral symmetry and its spontaneous breaking play an important role both in the light
hadron and heavy hadron systems. The chiral perturbation theory (χ PT) is the low energy …

For many decades after the invention of the quark model in 1964 there was no evidence that
hadrons are formed from anything other than the simplest pairings of quarks and antiquarks …

In the past decade, exotic hadrons with charm and bottom flavors have been extensively
studied both in experiments and in theories. In this review, we provide topical discussions by …

Among the newly observed structures in the heavy-quarkonium mass region, some have
been proposed to be hadronic molecules. We investigate the consequences of heavy-quark …

The past decade witnessed a remarkable proliferation of exotic charmonium-like
resonances discovered at accelerators. In particular, the recently observed charged states …