524 research outputs found
Anomalous Dimensions of Conformal Baryons
We determine the anomalous dimensions of baryon operators for the three color
theory as function of the number of massless flavours within the conformal
window to the maximum known order in perturbation theory. We show that the
anomalous dimension of the baryon is controllably small, within the
-expansion, for a wide range of number of flavours. We also find that
this is always smaller than the anomalous dimension of the fermion mass
operator. These findings challenge the partial compositeness paradigm.Comment: 4 pages, 4 figures. Matches published versio
Beta Function and Anomalous Dimensions
We demonstrate that it is possible to determine the coefficients of an
all-order beta function linear in the anomalous dimensions using as data the
two-loop coefficients together with the first one of the anomalous dimensions
which are universal. The beta function allows to determine the anomalous
dimension of the fermion masses at the infrared fixed point, and the resulting
values compare well with the lattice determinations.Comment: Version to match the published one in Phys. Rev. D. We added several
tables demonstrating how well the prediction for the anomalous dimensions at
the fixed point obtained via the all-orders beta function compares with the
one obtained in perturbation theory. We added also a figur
Hot Conformal Gauge Theories
We compute the nonzero temperature free energy up to the order g^6 \ln(1/g)
in the coupling constant for vector like SU(N) gauge theories featuring matter
transforming according to different representations of the underlying gauge
group. The number of matter fields, i.e. flavors, is arranged in such a way
that the theory develops a perturbative stable infrared fixed point at zero
temperature. Due to large distance conformality we trade the coupling constant
with its fixed point value and define a reduced free energy which depends only
on the number of flavors, colors and matter representation.
We show that the reduced free energy changes sign, at the second, fifth and
sixth order in the coupling, when decreasing the number of flavors from the
upper end of the conformal window. If the change in sign is interpreted as
signal of an instability of the system then we infer a critical number of
flavors. Surprisingly this number, if computed to the order g^2, agrees with
previous predictions for the lower boundary of the conformal window for
nonsupersymmetric gauge theories. The higher order results tend to predict a
higher number of critical flavors. These are universal properties, i.e. they
are independent on the specific matter representation.Comment: RevTeX, 2-columns, 10 pages, 10 figure
Ideal Walking Dynamics via a Gauged NJL Model
According to the Ideal Walking Technicolor paradigm large mass anomalous
dimensions arise in gauged Nambu--Jona-Lasinio (NJL) models when the
four-fermion coupling is sufficiently strong to induce spontaneous symmetry
breaking in an otherwise conformal gauge theory. We therefore study the
gauged NJL model with two adjoint fermions using lattice simulations. The model
is in an infrared conformal phase at small NJL coupling while it displays a
chirally broken phase at large NJL couplings. In the infrared conformal phase
we find that the mass anomalous dimension varies with the NJL coupling reaching
close to the chiral symmetry breaking transition, de facto
making the present model the first explicit realization of the Ideal Walking
scenario.Comment: 10 pages, 4 tables and 7 figure
Baryon currents in QCD with compact dimensions
On a compact space with non-trivial cycles, for sufficiently small values of
the radii of the compact dimensions, SU(N) gauge theories coupled with fermions
in the fundamental representation spontaneously break charge conjugation, time
reversal and parity. We show at one loop in perturbation theory that physical
signature for this phenomenon is a non-zero baryonic current wrapping around
the compact directions. The persistence of this current beyond the perturbative
regime is checked by lattice simulations.Comment: Minor changes, typos corrected; version accepted for publication in
Phys. Rev.
Fermions in higher representations. Some results about SU(2) with adjoint fermions
We discuss the lattice formulation of gauge theories with fermions in
arbitrary representations of the color group, and present the implementation of
the RHMC algorithm for simulating dynamical Wilson fermions. A first dataset is
presented for the SU(2) gauge theory with two fermions in the adjoint
representation, which has been proposed as a possible technicolor candidate.
Simulations are performed on 8^3x16 lattices, at fixed lattice spacing. The
PCAC mass, the pseudoscalar, vector and axial meson masses, the pseudoscalar
meson decay constant are computed. The extrapolation to the chiral limit is
discussed. However more extensive investigations are needed in order to control
the systematic errors in the numerical results, and then understand in detail
the phase structure of these theories.Comment: 7 pages, 3 figures. Talk presented at the XXVI International
Symposium on Lattice Field Theory, July 14-19, 2008, Williamsburg, VA, US
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