Gluon-propagator functional form in the Landau gauge in SU(3) lattice QCD: Yukawa-type gluon propagator and anomalous gluon spectral function

Abstract

We study the gluon propagator $D_{\mu \nu }^{ab}(x)$ in the Landau gauge in SU(3) lattice QCD at $\beta$ = 5.7, 5.8, and 6.0 at the quenched level. The effective gluon mass is estimated as $400\sim 600$MeV for $r\equiv (x_{\alpha }{x}_{\alpha }{)}^{1/2}=0.5\sim 1.0$ fm. Through the functional-form analysis of $D_{\mu \nu }^{ab}(x)$ obtained in lattice QCD, we find that the Landau-gauge gluon propagator $D_{\mu \mu }^{aa}(r)$ is well described by the Yukawa-type function $e^{-mr}/r$ with $m\simeq 600$MeV for $r=0.1\sim 1.0$ fm in the four-dimensional Euclidean space-time. In the momentum space, the gluon propagator ${\tilde{D}}_{\mu \mu }^{aa}(p^2)$ with $(p^2{)}^{1/2}=0.5\sim 3$ GeV is found to be well approximated with a new-type propagator of $(p^2+m^2{)}^{-3/2}$, which corresponds to the four-dimensional Yukawa-type propagator. Associated with the Yukawa-type gluon propagator, we derive analytical expressions for the zero-spatial-momentum propagator $D_0(t)$, the effective mass $M_{\mathrm{eff}}(t)$, and the spectral function $\rho (\omega )$ of the gluon field. The mass parameter $m$ turns out to be the effective gluon mass in the infrared region of $\sim$ 1fm. As a remarkable fact, the obtained gluon spectral function $\rho (\omega )$ is almost negative-definite for $\omega >m$, except for a positive $\delta$-functional peak at $\omega =m$.

Comments: 20 pages, 15 figures