自由电子气体的费米量计算规律的探讨

通过对自由电子气体的费米量计算规律的探讨,归纳和总结了费米系统的宏观量计算的一般规律.

Multiple solutions and fermion mass effect in QED_3

Due to the negligible non-perturbation effect in the low-energy region, quantum chromodynamics （QCD） is limited to be applied to hadron problems in particle physics. However, QED has mature non-perturbation models which can be applied to Fermi acting-energy between quark and gluon. This paper applies quantum electrodynamics in 2 ＋ 1 dimensions （QED3） to the Fermi condensation problems. First, the Dyson-Schwinger equation which the fermions satisfy is constructed, and then the Fermi energy gap is solved. Theoretical calculations show that within the chirality limit, there exist three solutions for the energy gap; beyond the chirality limit, there are two solutions; all these solutions correspond to different fermion condensates. It can be concluded that the fermion condensates within the chirality limit can be used to analyze the existence of antiferromagnetic, pseudogap, and superconducting phases, and two fermion condensates are discovered beyond the chirality limit.

Conservation Laws and Symmetries of the Levi Equation

The conservation laws of the Levi equation are presented.Two types of symmetry of the Levi equationhierarchy are deduced.Further it is proved that these symmetries construct an infinite-dimensional Lie algebra.

Functional Integrals and Collective Excitations in Boson-Fermion Model

In this paper, collective excitations in the boson-fermion model are investigated by means of functional integration method. The equations of energy gap and excitation spectrum are derived. Moreover, the Bose energy spectrum of zero wave vector Fermi fields is also calculated.

Neutron Star Magnetic Field as for Nonzero Photon Mass

We investigate the neutron star magnetic field by the relative mean-field theory, where the photon effective mass depending on baryon density of charged particles is nonzero. This field is produced by star itself, which is the function of baryon density. The result fits the observations.

Fermion Corrections to Mass of Scalar Glueball in QCD Sum Rule

Contributions of fermions to the mass of the scalar glueball 0++are calculated at two-loop level in theframework of QCD sum rules.It slightly changes the coefficients in the operator product expansion （OPE） and shiftsthe mass of glueball to 1.72 ± 0.07 GeV.

Electron Dispersion in Liquid Alkali and Their Alloys

Ashcroft＇s local empty core （EMC） model pseudopotential in the second-order perturbation theory is used to study the electron dispersion relation, the Fermi energy, and deviation in the Fermi energy from free electron value for the liquid alkali metals and their equiatomic binary alloys for the first time. In the present computation, the use of pseudo-alloy-atom model （PAA） is proposed and found successful. The influence of the six different forms of the local field correction functions proposed by Hartree （H）, Vashishta Singwi （VS）, Taylor （T）, lehimaru-Utsumi （IU）, Farid et al. （F）, and Sarkar et al. （S） on the aforesaid electronic properties is examined explicitly, which reflects the varying effects of screening. The depth of the negative hump in the electron dispersion of liquid alkalis decreases in the order Li --→ K, except for Rb and Cs, it increases. The results of alloys are in predictive nature.

Magnetic Manipulation of Massless Dirac Fermions in Graphene Quantum Dot

We have theoretically analyzed the quasibound states in a Mraphene quantum dot （GO, D） with a magnetic flux -φ in the centre. It is shown that the two-fold time reversal degeneracy is broken and the quasibound states of GQD with positive^negative angular momentum shifted upwards/downwards with increasing the magnetic flux. The variation of the quasibound energy depends linearly on the magnetic flux, which is quite different from the parabolic relationship for SchrSdinger electrons. The GQD＇s quasibound states spectrum shows an obvious Aharonov-Bohm （AB） oscillations with the magnetic flux. It is also shown that the quasibound state with energy equal to the barrier height becomes a bound state completely confined in GQD.

Associated Production of Z Boson and a Pair of New Quarks at LHC

The associated production of Z boson and a pair of new quarks at the Large Hadron Collider （LHC） is studied. The cross sections for both sequential fermions and vector-like fermions are presented. It is found that for sequential fermions the cross sections can reach 1 - 10^2 /b for heavy quark mass mQ from 1000 GeV to 200 GeV. For vector-like quarks, the cross sections are suppressed by mixing parameter sin OL. Focusing on process pp → b＇b＇, we investigate the possibility of detecting the 6l 4- 2j signal. For a b＇ with light mass and a large branching ratio of b＇ → bZ, it is found that only several signal events （ parton level ） can be produced with 1000 fb^-1 integrated luminosity. Although the signal events are rare, all the final states are produced centrally and multi lepton final states are clear at hadron collider, which could be easily detected.

Bell＇s Theorem Without Inequalities for Arbitrarily High-Dimensional Fermionic System

A generalized proof of Bell's theorem without inequalities via the singlet state of two spin-(2n + 1)/2 fermionic particles for two observers is proposed. It is a direct and meaningful extension of that presented by A. Cabello [Phys. Rev. A67 (2003) 032107] and the proof from A. Cabello is included in our proof as a special example.

Two-Component Description for Relativistic Fermions

We propose a two-component form to describe massive relativistic fermions in gauge theories. Relations between the Green＇s functions in this form and those in the conventional four-component form are derived. It is shown that the S-matrix elements in both forms are exactly the same. The description of the fermion in the new form simplifies significantly the γ-matrix algebra in the four-component form. In particular, in perturbative calculations the propagator of the fermion is a scalar function. As examples, we use this form to reproduce the relativistic spectrum of hydrodron atom, the S-matrix of e＋e-→μ＋μ- and QED one-loop vacuum polarization of photon.

Quasiparticle Spectrum of Quantum Degenerate Fermi Gas in the Presence of Self—Consistent Magnetization Field

In this paper, we develop a systematic and simple method to derive quasiparticle spectrum of the quantum degenerate Fermi gases within the framework of Hartree–Fock–Bogoliubov theory which turns a general nonlinear two-body interaction Hamiltonian into a bilinear Hamiltonian by introducing certain self-consistent mean fields. Applying the approach, we obtain the quasi-particle spectrum of the model describing the superfluid phase transition that arises when a Feshbach resonance pairing occurs in a dilute Fermi gas in the presence of the magnetization fields and . When the gap parameter Δ is smaller than one or both of the magnetization fields, the spectrum manifests roton-type structure dramatically different from the spectrum in the absence of the magnetization fields.

Lattice QCD Calculation of ππ Scattering Length

We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the ＂Asqtad＂ improved staggered fermion formulation, we measure full ππ four-point correlators for isospin I = 0 and 2 channels, and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results. Extrapolating to the physical pion mass yields scattering lengths as mna01=2 = -0.041 6（2） and mna01= 0.186（2） for isospin I = 2 and 0 channels, respectively. Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study, where we include the disconnected contribution, and our preliminary result is near to its experimental value. These simulations are carried out with MILC 2 ＋ 1 flavor gauge configurations at lattice spacing a ≈0.15 fm.

Interaction between Fermions via Mass less Bosons and Massive Particles

By using a Hamiltonian based on the coupling through flux lines, we have calculated the interaction energy between two fermions via mass less bosons as well as via massive particles. In the case of interaction via mass less bosons we obtain an equivalent expression for the Coulomb＇s energy on the form cthc/r, where a is the fine structure constant. In the case of the interaction via massive particles we obtain that the interaction energy contains a term building the potential well. Also, we take into account the spin-spin interaction of the nucleons and we show that this interaction modulates the interaction potential through a cosine factor. The obtained results are in a good agreement with experimental data, for example, of deuteron. We have determined the radial functions for the deuteron.

Classification of Topological Insulators with Time-Reversal and Inversion Symmetry

In this paper, we find that topological insulators with time-reversal symmetry and inversion symmetry featuring two-dimensional quantum spin Hall （QSH） state can be divided into 16 classes, which are characterized by four Z2 topological variables ζk =0, 1 at four points with high symmetry in the Brillouin zone. We obtain the corresponding edge states for each one of these sixteen classes of QSHs. In addition, it is predicted that massless fermionic excitations appear at the quantum phase transition between different QSH states. In the end, we also briefly discuss the threedimensional case.

Joule-Thomson Coefficient for Strongly Interacting Unitary Fermi Gas

The Joule-Thomson effect reflects the interaction among constituent particles of macroscopic system.Forclassical ideal gas,the corresponding Joule-Thomson coefficient is vanishing while it is non-zero for ideal quantum gasdue to the quantum degeneracy.In recent years,much attention is paid to the unitary Fermi gas with infinite two-bodyscattering length.According to universal analysis,the thermodynamical law of unitary Fermi gas is similar to that ofnon-interacting ideal gas,which can be explored by the virial theorem P = 2E/3V.Based on previous works,we furtherstudy the unitary Fermi gas properties.The effective chemical potential is introduced to characterize the nonlinear levelscrossing effects in a strongly interacting medium.The changing behavior of the rescaled Joule-Thomson coefficientaccording to temperature manifests a quite different behavior from that for ideal Fermi gas.

Localized 4f-electrons in the quantum critical heavy fermion ferromagnet CeRh_(6)Ge_(4)

Ferromagnetic quantum critical points were predicted to be prohibited in clean itinerant ferromagnetic systems,yet such a phenomenon was recently revealed in CeRh_(6)Ge_(4),where the Curie temperature can be continuously suppressed to zero under a moderate hydrostatic pressure.Here we report the observation of quantum oscillations in CeRh_(6)Ge_(4)from measurements using the cantilever and tunnel-diode oscillator methods in fields up to 45 T,clearly demonstrating that the ferromagnetic quantum criticality occurs in a clean system.In order to map the Fermi surface of CeRh_(6)Ge_(4),we performed angle-dependent measurements of quantum oscillations at ambient pressure,and compared the results to density functional theory calculations.The results are consistent with the Ce 4f electrons remaining localized and not contributing to the Fermi surface,suggesting that localized ferromagnetism is a key factor for the occurrence of a ferromagnetic quantum critical point in CeRh_(6)Ge_(4).

High-throughput screening for Weyl semimetals with S_(4) symmetry

Based on irreducible representations(or symmetry eigenvalues) and compatibility relations(CR), a material can be predicted to be a topological/trivial insulator(satisfying CR) or a topological semimetal(violating CR). However, Weyl semimetals(WSMs) usually go beyond this symmetry-based strategy. In other words, Weyl nodes could emerge in a material, no matter if its occupied bands satisfy CR, or if the symmetry indicators are zero. In this work, we propose a new topological invariant v for the systems with S4 symmetry(i.e., the improper rotation S_(4)(≡IC_(4z)) is a proper fourfold rotation(C_(4z)) followed by inversion(I)), which can be used to diagnose the WSM phase. Moreover, v can be easily computed through the onedimensional Wilson-loop technique. By applying this method to the high-throughput screening in our first-principles calculations, we predict a lot of WSMs in both nonmagnetic and magnetic compounds.Various interesting properties(e.g., magnetic frustration effects, superconductivity and spin-glass order,etc.) are found in predicted WSMs, which provide realistic platforms for future experimental study of the interplay between Weyl fermions and other exotic states.

Unveiling a critical stripy state in the triangular-lattice SU(4)spin-orbital model

The simplest spin-orbital model can host a nematic spin-orbital liquid state on the triangular lattice.We provide clear evidence that the ground state of the SU(4)Kugel-Khomskii model on the triangular lattice can be well described by a‘‘single”Gutzwiller projected wave function with an emergent parton Fermi surface,despite it exhibits strong finite-size effect in quasi-one-dimensional cylinders.The finite-size effect can be resolved by the fact that the parton Fermi surface consists of open orbits in the reciprocal space.Thereby,a stripy liquid state is expected in the two-dimensional limit,which preserves the SU(4)symmetry while breaks the translational symmetry by doubling the unit cell along one of the lattice vector directions.It is indicative that these stripes are critical and the central charge is c=3,in agreement with the SU(4)1Wess-Zumino-Witten conformal field theory.All these results are consistent with the Lieb-Schultz-Mattis-Oshikawa-Hastings theorem.

Superallowed Fermi transitions in RPA with a relativistic point-coupling energy functional

The self-consistent random phase approximation (RPA) approach with the residual interaction derived from a relativistic pointcoupling energy functional is applied to evaluate the isospin symmetry-breaking corrections δ c for the 0+ → 0+ superallowed Fermi transitions.With these δ c values,together with the available experimental f t values and the improved radiative corrections,the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is examined.Even with the consideration of uncertainty,the sum of squared top-row elements has been shown to deviate from the unitarity condition by 0.1% for all the employed relativistic energy functionals.