20,596 research outputs found

    Improved lattice QCD with quarks: the 2 dimensional case

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    QCD in two dimensions is investigated using the improved fermionic lattice Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved theory leads to a significant reduction of the finite lattice spacing errors. The quark condensate and the mass of lightest quark and anti-quark bound state in the strong coupling phase (different from t'Hooft phase) are computed. We find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures

    Phase Structure of Compact QED3QED_3 with Massless Fermions

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    In the framework of (2+1)-dimensional compact lattice QED with light fermions, we investigate the phase diagram in the (β,N)(\beta, N) plane. The approximations involved are related to an expansion of the effective fermionic action as a power series of the flavor number NN. We also develop a new mechanism for understanding the NN-critical phenomenon in the full theory. Our results for the specific heat indicate that only one phase does exist. We give strong evidences that this qualitative result should not be changed with the inclusion of higher order terms in the NN expansion.Comment: 10 pages and two figures; DFTUZ 92.2

    Exotic mesons from quantum chromodynamics with improved gluon and quark actions on the anisotropic lattice

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    Hybrid (exotic) mesons, which are important predictions of quantum chromodynamics (QCD), are states of quarks and anti-quarks bound by excited gluons. First principle lattice study of such states would help us understand the role of ``dynamical'' color in low energy QCD and provide valuable information for experimental search for these new particles. In this paper, we apply both improved gluon and quark actions to the hybrid mesons, which might be much more efficient than the previous works in reducing lattice spacing error and finite volume effect. Quenched simulations were done at β=2.6\beta=2.6 and on a ξ=3\xi=3 anisotropic 123×3612^3\times36 lattice using our PC cluster. We obtain 2013±26±712013 \pm 26 \pm 71 MeV for the mass of the 1+1^{-+} hybrid meson qˉqg{\bar q}qg in the light quark sector, and 4369±37±994369 \pm 37 \pm 99Mev in the charm quark sector; the mass splitting between the 1+1^{-+} hybrid meson cˉcg{\bar c}c g in the charm quark sector and the spin averaged S-wave charmonium mass is estimated to be 1302±37±991302 \pm 37 \pm 99 MeV. As a byproduct, we obtain 1438±32±571438 \pm 32 \pm 57 MeV for the mass of a P-wave 1++1^{++} uˉu{\bar u}u or dˉd{\bar d}d meson and 1499±28±651499 \pm 28 \pm 65 MeV for the mass of a P-wave 1++1^{++} sˉs{\bar s}s meson, which are comparable to their experimental value 1426 MeV for the f1(1420)f_1(1420) meson. The first error is statistical, and the second one is systematical. The mixing of the hybrid meson with a four quark state is also discussed.Comment: 12 pages, 3 figures. Published versio

    Thermodynamical quantities of lattice full QCD from an efficient method

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    I extend to QCD an efficient method for lattice gauge theory with dynamical fermions. Once the eigenvalues of the Dirac operator and the density of states of pure gluonic configurations at a set of plaquette energies (proportional to the gauge action) are computed, thermodynamical quantities deriving from the partition function can be obtained for arbitrary flavor number, quark masses and wide range of coupling constants, without additional computational cost. Results for the chiral condensate and gauge action are presented on the 10410^4 lattice at flavor number Nf=0N_f=0, 1, 2, 3, 4 and many quark masses and coupling constants. New results in the chiral limit for the gauge action and its correlation with the chiral condensate, which are useful for analyzing the QCD chiral phase structure, are also provided.Comment: Latex, 11 figures, version accepted for publicatio

    Bound States and Critical Behavior of the Yukawa Potential

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    We investigate the bound states of the Yukawa potential V(r)=λexp(αr)/rV(r)=-\lambda \exp(-\alpha r)/ r, using different algorithms: solving the Schr\"odinger equation numerically and our Monte Carlo Hamiltonian approach. There is a critical α=αC\alpha=\alpha_C, above which no bound state exists. We study the relation between αC\alpha_C and λ\lambda for various angular momentum quantum number ll, and find in atomic units, αC(l)=λ[A1exp(l/B1)+A2exp(l/B2)]\alpha_{C}(l)= \lambda [A_{1} \exp(-l/ B_{1})+ A_{2} \exp(-l/ B_{2})], with A1=1.020(18)A_1=1.020(18), B1=0.443(14)B_1=0.443(14), A2=0.170(17)A_2=0.170(17), and B2=2.490(180)B_2=2.490(180).Comment: 15 pages, 12 figures, 5 tables. Version to appear in Sciences in China

    Comment on "General nonlocality in quantum fields"

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    In this paper, we first incorporate the weak interaction into the theory of General Nonlocality by finding a appropriate metric for it. Accordingly, we suggest the theoretical frame of General Nonlocality as the candidate theory of unifying three microscope interactions in low energy limit. In this unifying scenario, the essential role of photon field is stressed.Comment: Only partial content published in the following reference. The part asserting the fermion mass problem now proved to be wrong, though remains in the versio

    Comment on "Time-Dependent Density-Matrix Renormalization Group: A Systematic Method for the Study of Quantum Many-Body Out-of- Equilibrium Systems"

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    In a recent Letter [Phys. Rev. Lett. 88, 256403(2002), cond-mat/0109158] Cazalilla and Marston proposed a time-dependent density- matrix renormalization group (TdDMRG) algorithm for the accurate evaluation of out-of-equilibrium properties of quantum many-body systems. For a point contact junction between two Luttinger liquids, a current oscillation develops after initial transient in the insulating regime. Here we would like to point out that (a) the observed oscillation is an artifact of the method; (b) the TdDMRG can be significantly improved by incorporating the non-equilibrium evolution of the goundstate into the density matrix.Comment: 1 page, 2 figure
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