The Running Coupling from SU(3) Potentials

We present data from the ALPHA Collaboration about lattice calculation of SU(2) pure--gauge running coupling constant, obtained with two different definitions of the coupling itself, which show universality of the continuum limit and clarify the applicability of renormalized perturbation theory.

We present results for the reference scale r_0 in SU(3) Lattice Gauge Theory for beta = 6/g_0^2 in the range 5.7 <= beta <= 6.57. The high relative accuracy of 0.3-0.6% in r_0/a was achieved through good statistics, the application of a multi-hit procedure and a variational approach in the computation of Wilson loops. A precise definition of the force used to extract r_0 has been used throughout the calculation which guarantees that r_0/a is a smooth function of the bare coup...

We have calculated the $q\bar q$ potential over a wide range of lattice separations on a $48^3\cdot56$ lattice at $\beta = 2.85$. We are able to investigate both long-range and (by correcting for the effects of lack of rotational invariance) short-range potentials. From the former we estimate the string tension and from the latter we are able to investigate asymptotic scaling. Fitting to this enables us to give an estimate for the $\Lambda$-parameter of pure-gauge SU(2).

We determine the three-loop coefficient of the beta function in the asymmetric momentum subtraction scheme in Landau gauge. This scheme is convenient for lattice studies of \alpha_s, the running coupling constant of QCD. We present high statistics lattice results for \alpha_s in the SU(3) Yang-Mills theory without quark, compare with the three-loop running and extract the value of the corresponding \Lambda_\msbar parameter. We estimate the systematic error coming from four-lo...

We present results on the spin-independent quark-antiquark potential in SU(3) gauge theory from a simulation on a 48^3*64 lattice at Beta = 6.8, corresponding to a volume of (1.7 fm)^3. Moreover, a comprehensive analysis of spin- and velocity-dependent potentials is carried out for SU(2) gauge theory, with emphasis on the short range structure, on lattices with resolutions ranging from .02 fm to .04 fm.

Schr\"odinger functional, the propagation kernel for going from some field configuration at time $x^0=0$ to some other configuration at $x^0=T$, is used to define a running coupling, $\bar g^2(L)$, at a length scale, $L$, in pure gauge theories. Using a lattice formulation and finite size scaling techniques, this running coupling is calculated non-perturbatively in the continuum for a wide range of $L$, that extends from the perturbative scales to non-perturbative scales, for...

The scaling behavior of pure gauge SU(3) in the region $\beta=5.85 - 7.60$ is examined by a Monte Carlo Renormalization Group analysis. The coupling shifts induced by factor 2 blocking are measured both on 32$^4$ and 16$^4$ lattices with high statistics. A systematic deviation from naive 2-loop scaling is clearly seen. The mean field and effective coupling constant schemes explain part, but not all of the deviation. It can be accounted for by a suitable change of coupling con...

In this Letter, we provide a determination of the coupling constant in three-flavor quantum chromodynamics (QCD), $\alpha^{\overline{\mathrm{MS}}}_s(\mu)$, for $\overline{\mathrm{MS}}$ renormalization scales $\mu \in (1,\,2)$ GeV. The computation uses gauge field configuration ensembles with $\mathcal{O}(a)$-improved Wilson-clover fermions generated by the Coordinated Lattice Simulations (CLS) consortium. Our approach is based on current-current correlation functions and has ...

We estimate the $\Lambda$-parameter in the $\overline{\mathrm{MS}}$ scheme for the SU(3) pure gauge theory with the twisted gradient flow method non-perturbatively. We obtain $\Lambda_{\overline{\mathrm{MS}}}/\sqrt{\sigma}=0.527(13)(10)$ and $r_{0}\Lambda_{\overline{\mathrm{MS}}}=0.605(15)(5)$ which are consistent with the known values.This demonstrates the validity of the present method.

One possibility for Beyond Standard Model physics is a new strongly-interacting gauge theory. One way to determine if a non-abelian gauge theory is QCD-like or conformal is to measure the running of the renormalized gauge coupling. We define the renormalized coupling from Wilson loop ratios, and measure these ratios via lattice simulations. We test this method in SU(3) pure gauge theory and show some first results for simulations with dynamical fermions in the fundamental rep...