303 research outputs found

    Effects of Nonperturbative Improvement in Quenched Hadron Spectroscopy

    Full text link
    We discuss a comparative analysis of unimproved and nonperturbatively improved quenched hadron spectroscopy, on a set of 104 gauge configurations, at beta=6.2. We also present here our results for meson decay constants, including the constants f_D and f_Ds in the charm-quark region.Comment: LATTICE98(spectrum

    SU(2) lattice gluon propagators at finite temperatures in the deep infrared region and Gribov copy effects

    Full text link
    We study numerically the SU(2) Landau gauge transverse and longitudinal gluon propagators at non-zero temperatures T both in confinement and deconfinement phases. The special attention is paid to the Gribov copy effects in the IR-region. Applying powerful gauge fixing algorithm we find that the Gribov copy effects for the transverse propagator D_T(p) are very strong in the infrared, while the longitudinal propagator D_L(p) shows very weak (if any) Gribov copy dependence. The value D_T(0) tends to decrease with growing lattice size; however, D_T(0) is non-zero in the infinite volume limit, in disagreement with the suggestion made in [1]. We show that in the infrared region D_T(p) is not consistent with the pole-type formula not only in the deconfinement phase but also for T < T_c. We introduce new definition of the magnetic infrared mass scale ('magnetic screening mass') m_M. The electric mass m_E has been determined from the momentum space longitudinal gluon propagator. We study also the (finite) volume and temperature dependence of the propagators as well as discretization errors.Comment: 11 pages, 14 figures, 3 tables. Few minor change

    The Minimal Landau Background Gauge on the Lattice

    Get PDF
    We present the first numerical implementation of the minimal Landau background gauge for Yang-Mills theory on the lattice. Our approach is a simple generalization of the usual minimal Landau gauge and is formulated for general SU(N) gauge group. We also report on preliminary tests of the method in the four-dimensional SU(2) case, using different background fields. Our tests show that the convergence of the numerical minimization process is comparable to the case of a null background. The uniqueness of the minimizing functional employed is briefly discussed.Comment: 5 pages, 1 tabl

    Numerical Study of Gluon Propagator and Confinement Scenario in Minimal Coulomb Gauge

    Get PDF
    We present numerical results in SU(2) lattice gauge theory for the space-space and time-time components of the gluon propagator at equal time in the minimal Coulomb gauge. It is found that the equal-time would-be physical 3-dimensionally transverse gluon propagator Dtr(k)D^{tr}(\vec{k}) vanishes at k=0\vec{k} = 0 when extrapolated to infinite lattice volume, whereas the instantaneous color-Coulomb potential D44(k)D_{44}(\vec{k}) is strongly enhanced at k=0\vec{k} = 0. This has a natural interpretation in a confinement scenario in which the would-be physical gluons leave the physical spectrum while the long-range Coulomb force confines color. Gribov's formula Dtr(k)=(k/2)[(k2)2+M4]1/2D^{tr}(\vec{k}) = (|\vec{k}|/2)[(\vec{k}^2)^2 + M^4]^{1/2} provides an excellent fit to our data for the 3-dimensionally transverse equal-time gluon propagator Dtr(k)D^{tr}(\vec{k}) for relevant values of k\vec{k}.Comment: 23 pages, 12 figures, TeX file. Minor modifications, incorporating referee's suggestion

    Numerical Study of the Ghost-Ghost-Gluon Vertex on the Lattice

    Full text link
    It is well known that, in Landau gauge, the renormalization function of the ghost-ghost-gluon vertex \widetilde{Z}_1(p^2) is finite and constant, at least to all orders of perturbation theory. On the other hand, a direct non-perturbative verification of this result using numerical simulations of lattice QCD is still missing. Here we present a preliminary numerical study of the ghost-ghost-gluon vertex and of its corresponding renormalization function using Monte Carlo simulations in SU(2) lattice Landau gauge. Data were obtained in 4 dimensions for lattice couplings beta = 2.2, 2.3, 2.4 and lattice sides N = 4, 8, 16.Comment: 3 pages, 1 figure, presented by A. Mihara at the IX Hadron Physics and VII Relativistic Aspects of Nuclear Physics Workshops, Angra dos Reis, Rio de Janeiro, Brazil (March 28--April 3, 2004

    The No-Pole Condition in Landau gauge: Properties of the Gribov Ghost Form-Factor and a Constraint on the 2d Gluon Propagator

    Get PDF
    We study the Landau-gauge Gribov ghost form-factor sigma(p^2) for SU(N) Yang-Mills theories in the d-dimensional case. We find a qualitatively different behavior for d=3,4 w.r.t. d=2. In particular, considering any (sufficiently regular) gluon propagator D(p^2) and the one-loop-corrected ghost propagator G(p^2), we prove in the 2d case that sigma(p^2) blows up in the infrared limit p -> 0 as -D(0)\ln(p^2). Thus, for d=2, the no-pole condition \sigma(p^2) 0) can be satisfied only if D(0) = 0. On the contrary, in d=3 and 4, sigma(p^2) is finite also if D(0) > 0. The same results are obtained by evaluating G(p^2) explicitly at one loop, using fitting forms for D(p^2) that describe well the numerical data of D(p^2) in d=2,3,4 in the SU(2) case. These evaluations also show that, if one considers the coupling constant g^2 as a free parameter, G(p^2) admits a one-parameter family of behaviors (labelled by g^2), in agreement with Boucaud et al. In this case the condition sigma(0) <= 1 implies g^2 <= g^2_c, where g^2_c is a 'critical' value. Moreover, a free-like G(p^2) in the infrared limit is obtained for any value of g^2 < g^2_c, while for g^2 = g^2_c one finds an infrared-enhanced G(p^2). Finally, we analyze the Dyson-Schwinger equation (DSE) for sigma(p^2) and show that, for infrared-finite ghost-gluon vertices, one can bound sigma(p^2). Using these bounds we find again that only in the d=2 case does one need to impose D(0) = 0 in order to satisfy the no-pole condition. The d=2 result is also supported by an analysis of the DSE using a spectral representation for G(p^2). Thus, if the no-pole condition is imposed, solving the d=2 DSE cannot lead to a massive behavior for D(p^2). These results apply to any Gribov copy inside the so-called first Gribov horizon, i.e. the 2d result D(0) = 0 is not affected by Gribov noise. These findings are also in agreement with lattice data.Comment: 40 pages, 2 .eps figure

    Some exact properties of the gluon propagator

    Full text link
    Recent numerical studies of the gluon propagator in the minimal Landau and Coulomb gauges in space-time dimension 2, 3, and 4 pose a challenge to the Gribov confinement scenario. We prove, without approximation, that for these gauges, the continuum gluon propagator D(k)D(k) in SU(N) gauge theory satisfies the bound d1d1(2π)dddkD(k)k2N{d-1 \over d} {1 \over (2 \pi)^d} \int d^dk {D(k) \over k^2} \leq N. This holds for Landau gauge, in which case dd is the dimension of space-time, and for Coulomb gauge, in which case dd is the dimension of ordinary space and D(k)D(k) is the instantaneous spatial gluon propagator. This bound implies that limk0kd2D(k)=0\lim_{k \to 0}k^{d-2} D(k) = 0, where D(k)D(k) is the gluon propagator at momentum kk, and consequently D(0)=0D(0) = 0 in Landau gauge in space-time d=2d = 2, and in Coulomb gauge in space dimension d=2d = 2, but D(0) may be finite in higher dimension. These results are compatible with numerical studies of the Landau-and Coulomb-gauge propagator. In 4-dimensional space-time a regularization is required, and we also prove an analogous bound on the lattice gluon propagator, 1d(2π)dππddkμcos2(kμ/2)Dμμ(k)4λsin2(kλ/2)N{1 \over d (2 \pi)^d} \int_{- \pi}^{\pi} d^dk {\sum_\mu \cos^2(k_\mu/2) D_{\mu \mu}(k) \over 4 \sum_\lambda \sin^2(k_\lambda/2)} \leq N. Here we have taken the infinite-volume limit of lattice gauge theory at fixed lattice spacing, and the lattice momentum componant kμk_\mu is a continuous angle πkμπ- \pi \leq k_\mu \leq \pi. Unexpectedly, this implies a bound on the {\it high-momentum} behavior of the continuum propagator in minimum Landau and Coulomb gauge in 4 space-time dimensions which, moreover, is compatible with the perturbative renormalization group when the theory is asymptotically free.Comment: 13 page

    Magnetic Screening in Hot Non-Abelian Gauge Theory

    Get PDF
    We analyze the large distance and low-momentum behavior of the magnetic gluon propagator of the SU(2) gauge theory at finite temperature. Lattice calculations within the 4-dimensional as well as the effective, dimensionally reduced 3-dimensional gauge theories in generalized Landau gauges and MAG show that the magnetic propagator is strongly infrared suppressed in Landau gauges but stays large and finite in MAG. Despite these differences in the low-momentum behavior of the propagator calculated in different gauges the magnetic fields are exponentially screened in all gauges considered. From the propagator calculated in maximally Abelian gauge we find for the screening mass, m_M = (1.48 +/- 0.17) T at T=2 T_c.Comment: 11 pages, LaTeX2e, new data added, conclusions unchanged. The final version to appear in Phys. Lett.
    corecore