Chiral Symmetry,Ward-Takahashi Identities and Mass Spectra in (2+1) Dimensional Chiral Gross-Neveu Model

Chiral Ward-Takahashi identities with composite fields are applied to investigate mass spectra in (2+1) dimensional chiral Gross-Neveu model.The fermion mass and bound state spectra are obtained,which are in agreement with large-N expansion in the lowest approximation.When the chiral symmetry is an approximate one,we obtain the PCAC.     

Chiral Bag Model at Finite Temperature

By taking the thermodynamical contributions of the pion mesons cloud outside the bag into account,the chiral bag model is extended to finite temperature.The temperature dependence of the radius of the chiral bag and the critical temperature of quark deconfinement are given.     

Chiral Phase Transition at Finite Isospin Density in Linear Sigma Model

Using the linear sigma model, we have introduced the pion isospin chemical potential. The chiral phase transition is studied at finite temperatures and finite isospin densities. We have studied the μ-T phase diagram for the chiral phase transition and found the transition cannot happen below a certain low temperature because of the Bose-Einstein condensation in this system. Above that temperature, the chiral phase transition is studied by the isotherms of pressure versus density. We indicate that the transition, in the chiral limit, is a first-order transition from a low-density phase to a high-density phase like a gas-liquid phase transition.     

(2+1)-Dimensional Fermion Determinant in a Constant Background Field at Finite Temperature and Density

We evaluate exactly both the nonrelativistic and relativistic fermion determinant in 2+1 dimensions in a constant background field at finite temperature. The effect of finite chemical potential is also considered. In both cases, the systems are decoupled into an infinite number of 1+1 fermions by Fourier transformation in the -variable. The total effective actions demonstrate nonextensiveness in the -dimension.     

Ward-Takahashi Identities and Mass Spectra in (2+1) Dimensional SU(2) Four-fermi Model

Ward-Takahashi identities with composite fields are utilized to inverstigate (2+1) dimensional model with SU(2) four-fermion couplings.When SU(2) chiral symmetry is both explicitly and dynamically broken,fermion mass is dynamically generated and mass spectra of the bound states are obtained The properties of vector and axial-vector currents are discussed.It turns out that the bound state π_α acquires a mass and the axial-vector current is partially conserved,and the Goldberger-Treimab relation is approximately valid in the case of small fermion current masses.     

Disappearance of Chiral Soliton Solutions and Chiral Phase Transition at High Temperature

The behavior of the chiral soliton model at high temperature is investigated.as well as the influence of thermal effects on the chiral soliton solutions and the fermion condensation is analysed.One possible physical mechanism is established,which is responsible for why there exists a difference between the critical temperature in deconfinement phase transition and that in chiral restoration phase transition.     

有限温度QED中的轫致辐射修正

用有限温度场论方法,通过计算费曼图分析了在QED中由于温度效应导致的新红外发散.结果表明零温场论中的红外发散和由温度效应引起的红外发散可以用描写虚过程的费曼图同时消除.计算了轫致辐射中光子的辐射几率,在Eikonal近似下所得到的结果和半经典近似给出的结果一致.     

Investigation of U(1) Lattice Gauge Model at Finite Temperature to Higher Order Expansion

The cumulant expansion of U(1) lattice gauge model at finite temperature (N_T=1) to the sixth order is presented. The variational parameters are determined by requiring thatthe corrections to the zeroth order approximation are the smallest. The order parameter,Polyakov line , converges well and is in good agreement with Monte Carlo simulations.Especially, the deconfinement phase transition point can be determined with accuracy.     

Structures of (ΩΩ)0 and (([1])Ω)1 in Extended Chiral SU(3) Quark Model

The structures of (ΩΩ)0 and (([1])Ω)1 are studied in the extended chiral SU(3) quark model in whichvector meson exchanges are included. The effect from the vector meson fields is very similar to that from the one-gluonexchange (OGE) interaction. Both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model,di-omega (ΩΩ)0 is always deeply bound, with over one hundred MeV binding energy, and (([1])Ω)1 ‘s binding energyis around 20 MeV. An analysis shows that the quark exchange effect plays a very important role for making di-omega(ΩΩ)0 deeply bound.     

Effects of Composite Pions on the Chiral Condensate within the PNJL Model at Finite Temperature

We investigate the effect of composite pions on the behaviour of the chiral condensate at finite temperature within the Polyakov-loop improved NJL model. To this end we treat quark-antiquark correlations in the pion channel (bound states and scattering continuum) within a Beth–Uhlenbeck approach that uses medium-dependent phase shifts. A striking medium effect is the Mott transition which occurs when the binding energy vanishes and the discrete pion bound state merges the continuum. This transition is triggered by the lowering of the continuum edge due to the chiral restoration transition. This in turn also entails a modification of the Polyakov-loop so that the SU(3) center symmetry gets broken at finite temperature and dynamical quarks (and gluons) appear in the system, taking over the role of the dominant degrees of freedom from the pions. At low temperatures our model reproduces the chiral perturbation theory result for the chiral condensate while at high temperatures the PNJL model result is recovered. The new aspect of the current work is a consistent treatment of the chiral restoration transition region within the Beth–Uhlenbeck approach on the basis of mesonic phase shifts for the treatment of the correlations.     

Calculation on U(1) Lattice Gauge Theory at Finite Temperature

The order parameter for the U(1) lattice gauge model at finite temperature with N_{τ=1 is calculated by using the variational-cumulant expansion method.The result is in agreement with the Monte Carlo simulations.The specific simplification in the case of Nτ=1 is discussed.The relationship between the variational method and the accumulation point method for determing the parameters introduced into the cumulant expansion is clarified.}     

2+1 Dimensional Noncommutative Dirac Oscillator and (Anti)-Jaynes-Cummings Models

We study Dirac oscillator in 2+1 dimensional noncommutative space. The model is solved exactly and the relationship with Jaynes-Cummings (JC) or anti-Jaynes-Cummings (AJC) models are investigated. We find that for a positive noncommutative parameter, there is an exact map from the 2+1 dimensional noncommutative Dirac oscillator to AJC model. However, for a negative noncommutative parameter, the noncommutative planar Dirac oscillator contains both AJC and JC terms simultaneously. Our investigation may afford a new way to study relativistic quantum mechanics models in noncommutative space by means of quantum optics method, and vice verse.     

Quantum Chromodynamics in 1+3 Dimensions at High Temperature: Dimensional Reduction Revisited

The gluon sector of QCD in 1+3 dimensions in analyzed at high temperature (much larger than the critical ones) thereby generalizing previous results by other authors. The imaginary time formalism is used. The analysis is carried out to all orders in an improved perturbation theory which includes all second-order internal quark loops in the “free” gluon propagators. General results are given for the leading high temperature contributions to all renormalized connected gluon Green's functions (for fixed external threemomenta, much smaller than the temperature). The latter are generated by a new (dimensionally reduced) high-temperature partition function Z_HT, which corresponds to: i) the Yang-Mills (“magnetic”) gluon field coupled to a massive scalar (“electric”) gluon field, all in 3 spatial dimensions and at zero imaginary time, ii) the quark field, which continues to depend on imaginary time, coupled to the above gluon fields Z_HT also depends on the renormalized quark masses and gauge coupling constant at zero temperature, the second order quark-loop contributions to the zero-temperature renormalization constants for the gluon field and the three and four gluon vertices and on new gluon mass terms. The latter correspond to a finite number of diagrams in the improved perturbation theory at high temperature. Z_HT could be useful as the starting point for further non-perturbative studies. For the pure Yang-Mills plus ghosts theory (no quarks), it is conjectured that contributions to Green's functions depending on external momenta due to internal electric gluons could be regarded, as subdominant. Arguments are given in order to justify that conjecture. Then, the above Z_HT can be simplified and another high-temperature generating functional depending only on magnetic gluon fields is given. For the full theory including quarks, the possibility of neglecting contributions due to internal quark loops is discussed: certain infrared divergences beyond the oneloop level appear to imply that such a simplification, although not discarded, is rather hard to establish.