Shu-Sheng Xu

Completing the Picture of the Roper Resonance.

We employ a continuum approach to the three valence-quark bound-state problem in relativistic quantum field theory to predict a range of properties of the protons radial excitation and thereby unify them with those of numerous other hadrons. Our analysis indicates that the nucleons first radial excitation is the Roper resonance. It consists of a core of three dressed quarks, which expresses its valence-quark content and whose charge radius is 80% larger than the proton analogue. That core is complemented by a meson cloud, which reduces the observed Roper mass by roughly 20%. The meson cloud materially affects long-wavelength characteristics of the Roper electroproduction amplitudes but the quark core is revealed to probes with Q(2)≳3m(N)(2).

Chiral phase transition with a chiral chemical potential in the framework of Dyson-Schwinger equations

Within the framework of Dyson-Schwinger equations , we discuss the chiral phase transition of QCD with a chiral chemical potential μ 5 as an additional scale. We focus especially on the issues related to the widely accepted as well as interesting critical end point (CEP). With the help of a scalar susceptibility, we find that there might be no CEP 5 in the T - μ 5 plane, and the phase transition in the T - μ 5 plane might be totally crossover when μ 50 MeV , which has apparent consistency with the lattice QCD calculation. Our study may also provide some useful hints to some other studies related to μ 5 .

Studies of two-solar-mass hybrid stars within the framework of Dyson-Schwinger equations

In this paper we introduce an equation of state (EOS) of quark matter within the framework of Dyson-Schwinger equations to study the structure of compact stars. The smooth crossover from hadronic matter to quark matter in the hybrid star is studied. We compare different strategies to obtain crossover EOSs and find a new way to construct two-solar-mass hybrid stars with even a relatively soft quark EOS, while earlier works showed that the quark EOS should be stiff enough to support a massive hybrid star.

Contact-interaction Faddeev equation and, inter alia , proton tensor charges

A confining, symmetry-preserving, Dyson-Schwinger equation treatment of a vector-vector contact interaction is used to formulate Faddeev equations for the nucleon and Delta-baryon in which the kernel involves dynamical dressed-quark exchange and whose solutions therefore provide momentum-dependent Faddeev amplitudes. These solutions are compared with those obtained in the static approximation and with a QCD-kindred formulation of the Faddeev kernel. They are also used to compute a range of nucleon properties, amongst them: the protons sigma-term; the large Bjorken-x values of separate ratios of unpolarised and longitudinally-polarised valence u- and d-quark parton distribution functions; and the protons tensor charges, which enable one to directly determine the effect of dressed-quark electric dipole moments (EDMs) on neutron and proton EDMs.

Continuum study of the QCD phase diagram through an OPE-modified gluon propagator

Within the Dyson-Schwinger equation framework, a gluon propagator model incorporating a quarks feedback through operator product expansion is introduced to investigate the QCD phase diagram in the temperature-chemical-potential (T - mu) plane. Partial restoration of chiral symmetry at zero temperature and finite temperature are both studied, suggesting a first order phase transition point on the mu axis and a critical end point at (T-E,mu(E))/T-c = (0.85,1.11), where T-c is the pseudocritical temperature. In addition, we find the pseudocritical line can be well parametrized with the curvature parameter. and a consistent decrease in., with more of the gluon propagator distributed to the quarks feedback.

Critical end point in the presence of a chiral chemical potential

A class of Polyakov-loop-modified Nambu\char21{}Jona-Lasinio models has been used to support a conjecture that numerical simulations of lattice-regularized QCD defined with a chiral chemical potential can provide information about the existence and location of a critical end point in the QCD phase diagram drawn in the plane spanned by baryon chemical potential and temperature. That conjecture is challenged by conflicts between the model results and analyses of the same problem using simulations of lattice-regularized QCD (lQCD) and well-constrained Dyson-Schwinger equation (DSE) studies. We find the conflict is resolved in favor of the lQCD and DSE predictions when both a physically motivated regularization is employed to suppress the contribution of high-momentum quark modes in the definition of the effective potential connected with the Polyakov-loop-modified Nambu\char21{}Jona-Lasinio models and the four-fermion coupling in those models does not react strongly to changes in the mean field that is assumed to mock-up Polyakov-loop dynamics. With the lQCD and DSE predictions thus confirmed, it seems unlikely that simulations of lQCD with

2+1 flavors QCD equation of state at zero temperature within Dyson–Schwinger equations

{\ensuremath{\mu}}_{5}g0

Proper time regularization at finite quark chemical potential

can shed any light on a critical end point in the regular QCD phase diagram.

Susceptibilities and critical exponents within the Nambu–Jona-Lasinio model

Within the framework of Dyson–Schwinger equations (DSEs), we discuss the equation of state (EOS) and quark number densities of 2+1 flavors, that is to say, u, d, and s quarks. The chemical equilibrium and electric charge neutrality conditions are used to constrain the chemical potential of different quarks. The EOS in the cases of 2 flavors and 2+1 flavors are discussed, and the quark number densities, the pressure, and energy density per baryon are also studied. The results show that there is a critical chemical potential for each flavor of quark, at which the quark number density turns to nonzero from 0; and furthermore, the system with 2+1 flavors of quarks is more stable than that with 2 flavors in the system. These discussions may provide some useful information to some research fields, such as the studies related to the QCD phase transitions or compact stars.

Pion and kaon valence-quark quasiparton distributions

In this paper, we use the two-flavor Nambu–Jona-Lasinio (NJL) model to study the quantum chromodynamics (QCD) chiral phase transition. To deal with the ultraviolet (UV) issue, we adopt the popular proper time regularization (PTR), which is commonly used not only for hadron physics but also for the studies with magnetic fields. This regularization scheme can introduce the infrared (IR) cutoff to include quark confinement. We generalize the PTR to zero temperature and finite chemical potential case use a completely new method, and then study the chiral susceptibility, both in the chiral limit case and with finite current quark mass. The chiral phase transition is second-order in μ = 0 and T = 0 and crossover at μ≠0 and T = 0. Three sets of parameters are used to make sure that the results do not depend on the parameter choice.