arXiv subjects
Publications and source records attributed to Viljami Leino.
We report progress towards computing the heavy quark momentum diffusion coefficient from the lattice correlator of two chromoelectric fields attached to a Polyakov loop in pure SU(3) gauge theory. Using a multilevel algorithm and tree-level improvement, we study the behavior of the diffusion coefficient as a function of temperature in the wide range $1.1 < T/Tc < 10^4$.
We present a novel approach to compute the force between a static quark and a static antiquark from lattice gauge theory directly, rather than extracting it from the static energy. We explore this approach for SU(3) pure gauge theory using the multilevel algorithm and smeared operators.
We present the first numerical study of the ultraviolet dynamics of non-asymptotically free gauge-fermion theories at large number of matter fields. As testbed theories we consider non-abelian SU(2) gauge theories with 24 and 48 Dirac fermions on the lattice. For these number of flavors asymptotic freedom is lost and the theories are governed by a gaussian fixed point at low energies. In the ultraviolet they can develop a physical cutoff and therefore be trivial, or achieve an interacting safe fixed point and therefore be fundamental at all energy scales. We demonstrate that the gradient flow method can be successfully implemented and applied to determine the renormalized running coupling when asymptotic freedom is lost. Additionally, we prove that our analysis is connected to the gaussian fixed point as our results nicely match with the perturbative beta function. Intriguingly, we observe that it is hard to achieve large values of the renormalized coupling on the lattice. This might be an early sign of the existence of a physical cutoff and imply that a larger number of flavors is needed to achieve the safe fixed point. A more conservative interpretation of the results is that the current lattice action is unable to explore the deep ultraviolet region where safety might emerge. Our work constitutes an essential step towards determining the ultraviolet fate of non asymptotically free gauge theories.
We review our recent results on the infrared behaviour of the SU(2) gauge theory with $N_f$ massless fundamental flavour fermions. We have analyzed the running of the coupling in SU(2) gauge theories with six and eight fermionic flavours using the gradient flow step scaling method. From the running of the coupling, we see a clear indication of an infrared stable fixed point in theories with six and eight flavours. These results are confirmed by our mass spectrum study, where we varied the number of flavours from two to six. We also compute the anomalous dimensions of mass and coupling.
We compute the running of the coupling in SU(2) gauge theory with six fermions in fundamental representation of the gauge group. We establish an infrared stable fixed point at strong coupling and measure also the anomalous dimension of the fermion mass operator at the fixed point. This theory therefore likely lies close to the boundary of the conformal window and will display novel infrared dynamics if coupled with the electroweak sector of the Standard Model.
We consider measurement of the leading irrelevant scaling exponent $γ_g^\ast$, given by the slope of the beta function, at the fixed point of SU(2) gauge theory with six or eight flavors. We use the running coupling measured using the gradient flow method and perform the continuum extrapolation by interpolating the measured beta function. We study also the dependence of the results on different discretization of the flow. For the eight flavor theory we find $γ_g^\ast=0.19(8)_{-0.09}^{+0.21}$. Applying the same analysis also for the six flavor theory, we find $γ_g^\ast=0.648(97)_{-0.1}^{+0.16}$ consistently with the earlier analysis.
We compute the spectrum of SU(2) gauge theory with two, four or six Dirac fermions in the fundamental representation of the gauge group. We investigate the scaling of the meson masses as a function of the quark mass when approaching the chiral limit. We find behavior compatible with the usual pattern of chiral symmetry breaking at $N_f\le 4$ and with the existence of an infrared fixed point at $N_f=6$. In the six flavor case we determine the anomalous dimension of the quark mass operator from the spectrum and find results fully consistent with earlier analyses.
We present the updated results of the infrared behavior of the SU(2) 6 and 8 fundamental representation fermions. We use the gradient flow method with the Schrödinger functional boundary conditions to measure the running of the coupling in these theories and find fixed points on both. We also measure the mass anomalous dimension from these configurations.
We study the evolution of the coupling in SU(2) gauge field theory with $N_f=8$ fundamental fermion flavors on the lattice. This model is expected to have an infrared fixed point at high coupling. We use HEX-smeared Wilson-clover action, and measure the gradient flow running coupling with Dirichlet boundary conditions. Extrapolating our results to continuum, we find an infrared fixed point at $g^2=8.24(59)^{+0.97}_{-1.64}$, with statistical and systematic error estimates. We also measure the anomalous dimension of the quark mass operator, and find its value at the fixed point $γ\approx 0.15 \pm 0.02$.
SU(2) with N_f = 6 and N_f = 8 are believed to have an infrared conformal fixed point. We use the spectral density method cross referenced with the mass step scaling method to evaluate the coupling constant dependence of the mass anomalous dimension for massless HEX smeared, clover improved Wilson fermions with Schrödinger functional boundary conditions.
We present preliminary results of the running of the coupling in SU(2) gauge theory with 6 massless fundamental representation fermion flavors. We measure the coupling using the gradient flow method with Schrödinger functional boundary conditions. The results are consistent with the perturbation theory in the weak coupling and we see an indication of an infrared fixed point at strong coupling.
SU(2) with Nf=8 is believed to have an infrared conformal fixed point. We use the spectral density method to evaluate the coupling constant dependence of the mass anomalous dimension for massless HEX smeared, clover improved Wilson fermions with Schrödinger functional boundary conditions.
We study the running of the coupling in SU(2) gauge theory with 8 massless fundamental representation fermion flavours, using the gradient flow method with the Schrödinger functional boundary conditions. Gradient flow allows us to measure robust continuum limit for the step scaling function. The results show a clear indication of infrared fixed point consistent with perturbation theory.
We present preliminary results of the gradient flow running coupling with Dirichlet boundary condition in the SU(2) gauge theory with 8 fermion flavours. Improvements to the gradient flow measurement allow us to obtain a robust continuum limit. The results are consistent with perturbative running in the weak coupling region.