73 research outputs found
Schwinger Model Mass Anomalous Dimension
The mass anomalous dimension for several gauge theories with an infrared
fixed point has recently been determined using the mode number of the Dirac
operator. In order to better understand the sources of systematic error in this
method, we apply it to a simpler model, the massive Schwinger model with two
flavours of fermions, where analytical results are available for comparison
with the lattice data.Comment: 7 pages, 3 figures, talk given at the 33rd International Symposium on
Lattice Field Theory, 14 - 18 July 2015, Kobe, Japan. Reference adde
(Dimensional) twisted reduction in large N gauge theories
We show that the spontaneous breaking of center symmetry can be avoided on a
lattice with the appropriate choice of twisted boundary
conditions. In order for this to work it is crucial that the twisted boundary
conditions are chosen in the reduced plane. This suggests that the choice of
twist tensor can influence the directions in which color and space degrees of
freedom become indistinguishable. We also present some preliminary quantitative
data comparing the value of the plaquette for different forms of reduction.Comment: Proceedings of the 33rd International Symposium on Lattice Field
Theory. References update
Anomalous dimensions of four-fermion operators from conformal EWSB dynamics
(Quasi)conformal scaling of composite operators from a strongly coupled EWSB
dynamics helps to produce the characteristic hierarchies exhibited by the
flavour couplings of the SM. It is however crucial to ensure that specific
models satisfy bounds on Higgs and flavour dynamics; this in turn requires to
control not only the anomalous dimensions of bilinears, but also those of
higher-dimensional operators. We report on an ongoing effort to determine
four-fermion operator anomalous dimensions, via Schr\"odinger Functional
techniques, in the benchmark scenario of Minimal Walking Technicolour.Comment: 7 pages, 2 figures, presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Mass anomalous dimension of Adjoint QCD at large N from twisted volume reduction
In this work we consider the gauge theory with two Dirac fermions in
the adjoint representation, in the limit of large . In this limit the
infinite-volume physics of this model can be studied by means of the
corresponding twisted reduced model defined on a single site lattice. Making
use of this strategy we study the reduced model for various values of up to
289. By analyzing the eigenvalue distribution of the adjoint Dirac operator we
test the conformality of the theory and extract the corresponding mass
anomalous dimension.Comment: 17 pages, 11 figures. Version to appear in JHEP - corrected typos and
reference
The twisted gradient flow running coupling
We measure the running of the 't Hooft coupling by performing a
step scaling analysis of the Twisted Eguchi-Kawai (TEK) model, the SU()
gauge theory on a single site lattice with twisted boundary conditions. The
computation relies on the conjecture that finite volume effects for SU(N) gauge
theories defined on a 4-dimensional twisted torus are controlled by an
effective size parameter , with the torus period. We
set the scale for the running coupling in terms of and use the
gradient flow to define a renormalized 't Hooft coupling .
In the TEK model, this idea allows the determination of the running of the
coupling through a step scaling procedure that uses the rank of the group as a
size parameter. The continuum renormalized coupling constant is extracted in
the zero lattice spacing limit, which in the TEK model corresponds to the large
limit taken at fixed value of . The coupling constant is
thus expected to coincide with that of the ordinary pure gauge theory at . The idea is shown to work and permits us to follow the evolution of
the coupling over a wide range of scales. At weak coupling we find a remarkable
agreement with the perturbative two-loop formula for the running coupling.Comment: 22 pages, 7 figure
`t Hooft model on the Lattice
Lattice results are presented for the meson spectrum of 1+1 dimensional gauge
theory at large , using the Twisted Eguchi-Kawai model. Comparison is made
to the results obtained by `t Hooft in the light cone gauge.Comment: pdflatex 7 page
Mass anomalous dimension in SU(2) with two adjoint fermions
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
Running of the coupling and quark mass in SU(2) with two adjoint fermions
We simulate SU(2) gauge theory with two massless Dirac fermions in the
adjoint representation. We calculate the running of the Schroedinger Functional
coupling and the renormalised quark mass over a wide range of length scales.
The running of the coupling is consistent with the existence of an infrared
fixed point (IRFP), and we find 0.07 < gamma < 0.56 at the IRFP, depending on
the value of the critical coupling.Comment: Talk presented at the XXVII International Symposium on Lattice Field
Theory, July 26-31, 2009, Peking University, Beijing, China; 7 pages, 4
figure
- âŠ