We study SU(2) lattice gauge theory with two flavours of Dirac fermions in the adjoint representation. We measure the running of the coupling in the Schroedinger Functional (SF) scheme and find it is consistent with existing results. We discuss how systematic errors affect the evidence for an infrared fixed point (IRFP). We present the first measurement of the running of the mass in the SF scheme. The anomalous dimension of the chiral condensate, which is relevant for phenomenological applications, can be easily extracted from the running of the mass, under the assumption that the theory has an IRFP. At the current level of accuracy, we can estimate 0.05 < gamma < 0.56 at the IRFP.Comment: 30 pages, 11 figure

We present the results of a systematic, first-principles study of the spectrum and decay constants of mesons for different numbers of color charges N , via lattice computations. We restrict our attention to states in the non-zero isospin sector, evaluating the masses associated with the ground-state and first excitation in the pseudoscalar, vector, scalar, and axial vector channels. Our results are based on a new set of simulations of four dimensional SU(N ) Yang-Mills theories with the number of colors ranging from N = 2 to N = 17; the spectra and the decay constants are computed in the quenched approximation (which becomes exact in the 't Hooft limit) using Wilson fermions. After discussing the extrapolations to the chiral and large-N limits, we present a comparison of our results to some of the numerical computations and analytical predictions available in the literature -including, in particular, those from holographic computations.

We simulate SU(2) gauge theory with six massless fundamental Dirac fermions. We measure the running of the coupling and the mass in the Schroedinger Functional scheme. We observe very slow running of the coupling constant. We measure the mass anomalous dimension gamma, and find it is between 0.135 and 1.03 in the range of couplings consistent with the existence of an IR fixed point.Comment: 14 pages, 4 figures; v3: published versio

We present an improved study of spectroscopic observables in the SU(2) Yang-Mills theory with two adjoint fermions. We make an improvement on the precision of previous results which clarify the scale of finite volume effects present. This analysis adds to the evidence for near-conformal dynamics of this theory, while indicating a preference for a low anomalous mass dimension of the massless theory. CERN-PH-TH Minimal Walking TechnicolorThe mechanism of dynamical electro-weak symmetry breaking (often referred to as technicolor) [1] remains a possible explanation for the breaking of the electro-weak symmetry observed in nature. Gauge theories which possess an approximate infra-red fixed point have been proposed as preferred candidates for the technicolor sector in models of extended technicolor [2] as it has been argued that they would allow suppression of flavour changing neutral currents while permitting generation of large fermion masses. This is achieved through the non-trivial renormalisation dynamics between the technicolor and extended technicolor scales. This property of the theory has been coined "walking" in reference to the slow running of the coupling between the two scales 1 .We can hope to generate an infra-red fixed point in a gauge theory, while minimising contributions to electroweak precision constraints, by adding a low number of fermion flavours in higher gauge representations to a gauge theory with a low number of colours. For these reasons the gauge theory theory with symmetry group SU(2) and two flavours of Dirac fermion in the adjoint representation has been termed minimal walking technicolor (MWT) [4].Conformal or near-conformal dynamics have not been conclusively identified in any theory as yet, although there are encouraging hints from a number of sources. Due to the non-perturbative nature of the problem, much of the investigation of this problem has arisen from lattice simulations, and this activity is growing. Some recent lattice studies of MWT [5,6,7] have attempted to identify a near-conformal behaviour directly from the behaviour of the coupling and anomalous dimensions of the theory under renormalisation flow. Others [8,9,10,11,12,13], including this work, perform measurements of physical observables in the theory and from their behaviour attempt to identify signals of near-conformal dynamics.This study builds on previous work in [9,13]. In particular we seek to support these results and establish their reliability by investigating the effect of performing measurements and analysis using alternative methods. In addition, through this we expect to ascertain the scale of systematic uncertainties present, which have as yet been largely unexplored. Signals of ConformalityThe question of whether MWT in the chiral limit posesses an actual infra-red fixed point, i.e. it lies within the conformal window, or an approximate fixed point, has not been conclusively answered. Nevertheless, it is clear that MWT with a non-zero fermion mass and defined in a finite volume, as simulated on the lat...