Abstract
Non-Abelian gauge theories with fermions transforming in the adjoint representation of the gauge group (AdjQCD) are a fundamental ingredient of many models that describe the physics beyond the Standard Model. Two relevant examples are N=1 Supersymmetric Yang-Mills (SYM) theory and Minimal Walking Technicolor, which are gauge theories coupled to one adjoint Majorana and two adjoint Dirac fermions, respectively. While confinement is a property of N=1 SYM, Minimal Walking Technicolor is expected to be infrared conformal. We study the propagators of ghost and gluon fields in the Landau gauge to compute the running coupling in the MiniMom scheme. We analyze several different ensembles of lattice Monte Carlo simulations for the SU(2) adjoint QCD with Nf=1/2, 1, 3/2, and 2 Dirac fermions. We show how the running of the coupling changes as the number of interacting fermions is increased towards the conformal window.
Highlights
Strong interactions are responsible for the confinement of quarks and for the generation of the hadron masses in QCD.The coupling (g or α ≡ g2 4π )of the strong interactions as a function of the energy scale μ decreases at high energies and asymptotic freedom allows a description of the interactions in a perturbative framework
We explore the nonperturbative dynamics of gluons and ghosts in the Landau gauge by means of numerical lattice simulations for an SU(2) gauge theory coupled to one, two, three and four Majorana fermions, corresponding to Nf 1⁄4 1=2, 3=2, and 2 Dirac fermions
We investigate how the ghost and gluon propagators and the running coupling change when the number of fermions is increased starting from a confining theory, N 1⁄4 1 supersymmetric Yang-Mills (SYM), to the point where the conformal window is reached at Nf 1⁄4 2
Summary
We investigate how the ghost and gluon propagators and the running coupling change when the number of fermions is increased starting from a confining theory, N 1⁄4 1 SYM, to the point where the conformal window is reached at Nf 1⁄4 2. The running of the coupling freezes, and gluon and ghost propagators both diverge following a power law in the infrared limit These conclusions arise from the solutions of coupled DSEs. In [8,9] the onset of the conformal window for fermions in the fundamental representation has been investigated applying this DysonSchwinger approach. The perturbative calculation will be used to compute the Λ-parameter of the adjoint QCD (AdjQCD) with different numbers of fermions in the MOM scheme and to verify whether our simulations are in a region where the lattice spacing is small enough such that the coupling at high energies follows the asymptotic scaling. Similar methods have been widely employed in previous lattice calculations of the running coupling for many BSM theories in the Schrödinger functional or the Wilson flow schemes [28,29,30,31,32,33,34], we will not attempt to use step scaling at directly zero fermion mass but we will compute the coupling from simulations at nonzero fermion mass produced by our collaboration to study the spectrum of bound states
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