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The explicit form of the correlation function for the most general local baryon operators is obtained for staggered fermions, in the center of mass. From the discrete symmetries of the action, it is shown that all operators couple to spin-12 states only. The whole physical information coming from any numerical simulation, including parity assignments, can be extracted from only one real function of the lattice time. All other correlation functions which can be measured vanish in the limit of large samples of gauge configurations, which may be used as a measure of the statistical significance of data.  相似文献   

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By Monte Carlo simulation on the lattice, we calculate the high-temperature behaviour of the energy density ? in SU(2) and SU(3) QCD with Wilson fermions. From the leading term of the hopping parameter expansion, we find that ? converges very rapidly to the Stefan-Boltzmann limit of an asymptotically free quark-gluon gas. The behaviour in the non-asymptotic region indicates that chiral symmetry restoration occurs at a higher temperature (Tch) than colour deconfinement (Tc), with TchTc ≈ 1.3.  相似文献   

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A large number of one-loop integrals emerging in a gauge perturbation theory on a lattice with Wilson fermions at r = 1 are evaluated with the use of the Burgio-Caracciolo-Pelissetto algorithm and the FORMpackage. In the bosonic case, an explicit analytical form of the recursion relations is presented.  相似文献   

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The chiral properties of the continuum limit of lattice QCD with Wilson fermions are studied. We show that a partially conserved axial current can be defined, satisfying the usual current algebra requirements.A proper definition of the chiral symmetry order parameter, 〈0|ψψ|0〉, is given, and the chiral properties of composite operators are investigated. The implications of our analysis to the lattice determination of non-leptonic weak amplitudes are also discussed.  相似文献   

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We address a long standing problem regarding topology in lattice simulations of QCD with unimproved Wilson fermions. Earlier attempt with unimproved Wilson fermions at β=5.6 to verify the suppression of topological susceptibility with decreasing quark mass (mq) was unable to unambiguously confirm the suppression. We carry out systematic calculations for two degenerate flavours at two different lattice spacings (β=5.6 and 5.8). The effects of quark mass, lattice volume and the lattice spacing on the spanning of different topological sectors are presented. We unambiguously demonstrate the suppression of the topological susceptibility with decreasing quark mass, expected from chiral Ward identity and chiral perturbation theory.  相似文献   

9.
Two possible ways of extending Symanzik's improvement programme to lattice fermions namely improvement to first and second order in the lattice sppacing a are discussed. The corresponding lattice actions for fermions are constructed and tree-level improvement conditions are derived by considering “classical” improvement. The concept of “on-shell” improvement is generalized to the lattice fermions studied here and the free parameters are determined for O(a) and O(a2) on-shell improved actions to all orders of perturbation theory. No evidence is found that the complicated structure of the O(a2) on-shell improved action, especially thearising fermion contact terms can be removed beyond tree level. The effect of terms in the action that explicitly break chiral symmetry and therefore remove the phenomenon of species doubling are investigated by considering the energy-momentum relations of the arising tree-level improved actions. Our main result is that the O(a) improved action is a slightly modified Wilson fermion action can still be written with only nearest-neighbour fermion interactions.  相似文献   

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Using 4 flavors of staggered fermions at infinite gauge coupling, we compare various analytic results for the hadron spectrum with exact Monte Carlo simulations. Agreement with [O. Martin, Large N gauge theory at strong coupling with chiral fermion, PhD thesis, CALT-68-1048, 1983; O. Martin, B. Siu, Phys. Lett. B 131 (1983) 419; O. Martin, Phys. Lett. B 130 (1983) 411] is very good, at the level of a few percent. Our results give credence to a discrepancy between the baryon mass and the critical chemical potential, for which baryons fill the lattice at zero temperature and infinite gauge coupling. Independent determinations of the latter set it at about 30% less than the baryon mass. The likely explanation is that the nuclear attraction becomes strong at infinite gauge coupling.  相似文献   

11.
《Physics letters. [Part B]》1987,195(3):448-452
A lattice Thirring model is defined using a finite-element differencing scheme. The momentum-space propagator is calculated to second order in the coupling, and it is shown that the form of the ultraviolet divergence as the lattice spacing is taken to zero is identical to that found in continuum perturbation theory. This provides further evidence for the absence of fermion species-doubling present in most other lattice formulations.  相似文献   

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A diagrammatic approach to the evaluation of correlated variational wave functions for strongly interacting fermions is presented. Diagrammatic rules for the calculation of the one-particle density matrix and the Hubbard interaction are derived which are valid for arbitraryd-dimensional lattices. An exact evaluation of expectation values is performed in the limitd=. The wellknown Gutzwiller approximation is seen to become the exact result for the expectation value of the Hubbard Hamiltonian in terms of the Gutzwiller wave function ind=. An efficient procedure to correct the Gutzwiller approximation in finite dimensions is developed. A detailed discussion of expectation values ind= in terms of explicit antiferromagnetic wave functions is given. Thereby an approximate result for the ground state energy of the Hubbard model, obtained recently within a slave-boson approach, is recovered.  相似文献   

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《Nuclear Physics B》1996,478(3):687-719
We describe an algebraic algorithm which allows us to express every one-loop lattice integral with gluon or Wilson-fermion propagators in terms of a small number of basic constants which can be computed with arbitrary high precision. Although the presentation is restricted to four dimensions the technique can be generalized to every space dimension. Various examples are given, including the one-loop self-energies of the quarks and gluons and the renormalization constants for some dimension-three and dimension-four lattice operators. We also give a method to express the lattice free propagator for Wilson fermions in coordinate space as a linear function of its values in eight points near the origin. This is an essential step in order to apply the recent methods of Lüscher and Weisz to higher-loop integrals with fermions.  相似文献   

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The chiral symmetry breaking at strong coupling in lattice QCD for naive and Wilson fermion cases is investigated by the Green function method with the Hartre-Fock approximation. Solving the coupled equations of the Green functions for the composite fields we compute the pion mass which directly satisfies the current algebra mass formula for both fermion cases.  相似文献   

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The topological charge density and topological susceptibility are determined by a multi-probing approximation using overlap fermions in quenched SU(3) gauge theory. Then we investigate the topological structure of the quenched QCD vacuum, and compare it with results from the all-scale topological density. The results are consistent.Random permuted topological charge density is used to check whether these structures represent underlying ordered properties. The pseudoscalar glueball mass is extracted from the two-point correlation function of the topological charge density. We study 3 ensembles of different lattice spacing a with the same lattice volume 16~3×32. The results are compatible with the results of all-scale topological charge density, and the topological structures revealed by multi-probing are much closer to all-scale topological charge density than those from eigenmode expansion.  相似文献   

20.
《Annals of Physics》1987,175(1):64-111
We present a novel numerical method for solving dynamical strong field problems in quantum mechanics and classical field theory based on expansion of functions in terms of splines. The method differs from traditional approaches by the introduction of a mapping onto a collocation lattice, which is generally nonuniform and time dependent depending on the particular physical application. This approach results in a set of finite matrix transformations of a type which can be evaluated rapidly on supercomputers possessing either vector or matrix coprocessors. As an example of the method, we present a study of the relativistic quantum-mechanical many-electron problem interacting via very strong time-dependent classical fields.  相似文献   

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