Chiral properties of quarkyonic matter and excited hadrons

Quantum-Chromo-Dynamics (QCD), a fundamental theory of strong interactions of quarks and gluons, at low temperatures and densities is realised in the confining mode with spontaneous breaking of chiral symmetry. It was recently argued that at moderate and low temperatures and reasonably large density a new phase must exist, called quarkyonic. A prominent feature is that the deconfining and chiral restoration phase transitions can be separated at low temperatures and consequently there should exist a confining but chirally symmetric matter. The only allowed excitations in this matter are confined but chirally symmetric hadrons. We want to carefully study this phase in order to understand it microscopically. Within this phase the hadron mass is generated with the manifestly chirally symmetric dynamics. This is consistent with a recent proposal of effective chiral restoration in excited hadrons at zero temperature and density. According to this scenario most of the mass of highly excited hadrons comes from the manifestly chirally-invariant dynamics. A definite prediction of this scenario is a decoupling of states from pions and small axial couplings. The diagonal axial couplings of excited states cannot be measured experimentally but can be studied on the lattice. We want to apply the lattice Monte-Carlo techniques to study the axial couplings of excited baryons to get the insight into their mass generation mechanism.

Hadrons, the strongly interacting particles, are made of quarks and gluons. A fundamental theory of quarks and gluons is Quantum-Chromo-Dynamics (QCD). There are two crucial properties of QCD confinement and chiral symmetry. Confinement means that only hadrons are directly observed, not quarks and gluons: Both quarks and gluons are confined inside hadrons. Masses of the u and d quarks are much smaller than masses of hadrons such as proton and neutron. We can approximately neglect these u and d masses. This property is called chiral symmetry. Masses of hadrons are generated due to both confinement and spontaneous (dynamical) breaking of chiral symmetry. We have studied a manifestation of spontaneous chiral symmetry breaking on observable hadron mass spectra. In particular, while this breaking is crucially important for masses of the ground states of hadrons, its effect is essentially reduced in hadrons with large spins. This is called the effective restoration of chiral symmetry. We have observed a survival of hadrons upon artificial restoration of chiral symmetry in computer simulations. It is complementary evidence that approximately chirally symmetric hadrons might exist high in the spectrum. This also suggests that there might exist a phase where a matter consists of chirally symmetric hadrons. A model for such a matter at low temperature and high density has been constructed and studied. As another aspect, we have connected the angular momentum content of some hadrons with the chiral symmetry breaking and studied it in computer simulations.