Chiral Phase Transition And Mesonic Superfluidity In QCD Matter

A fundamental question of physics is what happens to matter when it is extremely heated or compressed.At very high temperature and density,the fundamental degrees of freedom of the strong interaction,quarks and gluons,come into play and a transition from confined baryons and mesons to a state with deconfined quarks and gluons is expected.Quantum Chromodynamics(QCD,describes interactions between quarks and gluons)is the theory of strong interactions-one of the four fundamental interactions occurring in nature,and an essential part of the standard model of particle physics.It describes interactions between quarks and gluons.At low temperature and low density,the basic phase of QCD matter is confined hadron(include baryon and meson);at high temperature and/or high density,the confined hadron could be transformed to a deconfined quark-glon plasma(QGP).Thestudy of the possible phases and physical properties of QCD matter is at the focus of many research activities worldwide,such as the evolution of the early universe(also called "Big Bang"),the relativistic heavy ion collison(also called "little bang"),the inner core of neutron stars and so on.Recently,the influence of new dimension—such as the electromagnatic field and rotation-on the properties and possible phase transition of QCD matter has been rapidly growing interests.In this article,we discuss the influence of vector interection on the chiral transition phase diagram in the functional renormalization group framework and the influence of rotation on the mesonic superfluidity transition.Firstly,we study the phase diagram of two-flavor massless QCD at finite baryon den-sity by applying the functional renormalization group(FRG)for a quark-meson model with?,?,and ? mesons.The dynamical fluctuations of quarks,?,and ? are included in the flow equations,while the amplitudes of ? fields are also allowed to fluctuate.At high temperature the effects of the ? field on the phase boundary are qualitatively similar to the mean-field calculations;the phase boundary is shifted to the higher chemical potential region.As the temperature is lowered,however,the transition line bends back to the lower chemical poten-tial region,irrespective of the strength of the vector coupling.In our FRG calculations,the driving force of the low temperature first order line is the fluctuations rather than the quark density,and the effects of ? fields have little impact.At low temperature,the effective poten-tial at small ? field is very sensitive to the infrared cutoff scale,and this significantly affects our determination of the phase boundaries.The critical chemical potential at the tricritical point is affected by the ?-field effects but its critical temperature stays around the similar value.Secondely,we investigate the mesonic superfluidity in isospin matter under rotation.Using the two-flavor NJL effective model under the presence of global rotation,we demon-strate two important effects of the rotation on its phase structure:a rotational suppression of the scalar-channel condensates,in particular the pion superfluidity region;and a rotational enhancement of the rho superfluidity region with vector-channel condensate.A new phase diagram for isospin matter under rotation is mapped out on the ?-?I plane where three distinctive phases,corresponding to ?,?,? dominated regions respectively,are separated by a second-order line at low isospin chemical potential and a first-order line at high rotation which are further connected at a tri-critical point.