300 research outputs found
Signals of confinement in Green functions of SU(2) Yang-Mills theory
The vortex picture of confinement is employed to explore the signals of
confinement in Yang-Mills Green functions. By using SU(2) lattice gauge theory,
it has been well established that the removal of the center vortices from the
lattice configurations results in the loss of confinement. The running coupling
constant, the gluon and the ghost form factors are studied in Landau gauge for
both cases, the full and the vortex removed theory. In the latter case, a
strong suppression of the running coupling constant and the gluon form factor
at low momenta is observed. At the same time, the singularity of the ghost form
factor at vanishing momentum disappears. This observation establishes an
intimate correlation between the ghost singularity and confinement. The result
also shows that a removal of the vortices generates a theory for which
Zwanziger's horizon condition for confinement is no longer satisfied.Comment: 4 pages, 4 figure
Renormalization Flow of Bound States
A renormalization group flow equation with a scale-dependent transformation
of field variables gives a unified description of fundamental and composite
degrees of freedom. In the context of the effective average action, we study
the renormalization flow of scalar bound states which are formed out of
fundamental fermions. We use the gauged Nambu--Jona-Lasinio model at weak gauge
coupling as an example. Thereby, the notions of bound state or fundamental
particle become scale dependent, being classified by the fixed-point structure
of the flow of effective couplings.Comment: 25 pages, 3 figures, v2: minor corrections, version to appear in PR
TG7r1 channel model document for high rate PD communications
Purpose Providing channel models which allow a fair comparison of different physical layer (PHY) High Rate PD Communications proposals submitted to TG7r1 in response to the Call for Proposals (CFP). Notice This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein
Chiral Hierarchies, Compositeness and the Renormalization Group
A wide class of models involve the fine--tuning of significant hierarchies
between a strong--coupling ``compositeness'' scale, and a low energy dynamical
symmetry breaking scale. We examine the issue of whether such hierarchies are
generally endangered by Coleman--Weinberg instabilities. A careful study using
perturbative two--loop renormalization group methods finds that consistent
large hierarchies are not generally disallowed.Comment: 22 pp + 5 figs (uuencoded and submitted separately),
SSCL-Preprint-490; FERMI-PUB-93/035-
Non-perturbative dynamics and charge fluctuations in effective chiral models
We discuss the properties of fluctuations of the electric charge in the
vicinity of the chiral crossover transition within effective chiral models at
finite temperature and vanishing net baryon density. The calculation includes
non-perturbative dynamics implemented within the functional renormalization
group approach. We study the temperature dependence of the electric charge
susceptibilities in the linear sigma model and explore the role of quantum
statistics. Within the Polyakov loop extended quark-meson model, we study the
influence of the coupling of quarks to mesons and to an effective gluon field
on charge fluctuations. We find a clear signal for the chiral crossover
transition in the fluctuations of the electric charge. Accordingly, we stress
the role of higher order cumulants as probes of criticality related to the
restoration of chiral symmetry and deconfinement.Comment: 12 pages, 3 figure
Propagators in Coulomb gauge from SU(2) lattice gauge theory
A thorough study of 4-dimensional SU(2) Yang-Mills theory in Coulomb gauge is
performed using large scale lattice simulations. The (equal-time) transverse
gluon propagator, the ghost form factor d(p) and the Coulomb potential V_{coul}
(p) ~ d^2(p) f(p)/p^2 are calculated. For large momenta p, the gluon propagator
decreases like 1/p^{1+\eta} with \eta =0.5(1). At low momentum, the propagator
is weakly momentum dependent. The small momentum behavior of the Coulomb
potential is consistent with linear confinement. We find that the inequality
\sigma_{coul} \ge \sigma comes close to be saturated. Finally, we provide
evidence that the ghost form factor d(p) and f(p) acquire IR singularities,
i.e., d(p) \propto 1/\sqrt{p} and f(p) \propto 1/p, respectively. It turns out
that the combination g_0^2 d_0(p) of the bare gauge coupling g_0 and the bare
ghost form factor d_0(p) is finite and therefore renormalization group
invariant.Comment: 10 pages, 7 figure
The Thermal Renormalization Group for Fermions, Universality, and the Chiral Phase-Transition
We formulate the thermal renormalization group, an implementation of the
Wilsonian RG in the real-time (CTP) formulation of finite temperature field
theory, for fermionic fields. Using a model with scalar and fermionic degrees
of freedom which should describe the two-flavor chiral phase-transition, we
discuss the mechanism behind fermion decoupling and universality at second
order transitions. It turns out that an effective mass-like term in the fermion
propagator which is due to thermal fluctuations and does not break chiral
symmetry is necessary for fermion decoupling to work. This situation is in
contrast to the high-temperature limit, where the dominance of scalar over
fermionic degrees of freedom is due to the different behavior of the
distribution functions. The mass-like contribution is the leading thermal
effect in the fermionic sector and is missed if a derivative expansion of the
fermionic propagator is performed. We also discuss results on the
phase-transition of the model considered where we find good agreement with
results from other methods.Comment: References added, minor typos correcte
Brownian Motions on Metric Graphs
Brownian motions on a metric graph are defined. Their generators are
characterized as Laplace operators subject to Wentzell boundary at every
vertex. Conversely, given a set of Wentzell boundary conditions at the vertices
of a metric graph, a Brownian motion is constructed pathwise on this graph so
that its generator satisfies the given boundary conditions.Comment: 43 pages, 7 figures. 2nd revision of our article 1102.4937: The
introduction has been modified, several references were added. This article
will appear in the special issue of Journal of Mathematical Physics
celebrating Elliott Lieb's 80th birthda
(Meta-)stable reconstructions of the diamond(111) surface: interplay between diamond- and graphite-like bonding
Off-lattice Grand Canonical Monte Carlo simulations of the clean diamond
(111) surface, based on the effective many-body Brenner potential, yield the
Pandey reconstruction in agreement with \emph{ab-initio}
calculations and predict the existence of new meta-stable states, very near in
energy, with all surface atoms in three-fold graphite-like bonding. We believe
that the long-standing debate on the structural and electronic properties of
this surface could be solved by considering this type of carbon-specific
configurations.Comment: 4 pages + 4 figures, Phys. Rev. B Rapid Comm., in press (15Apr00).
For many additional details (animations, xyz files) see electronic supplement
to this paper at http://www.sci.kun.nl/tvs/carbon/meta.htm
Exact Flow Equations and the U(1)-Problem
The effective action of a SU(N)-gauge theory coupled to fermions is evaluated
at a large infrared cut-off scale k within the path integral approach. The
gauge field measure includes topologically non-trivial configurations
(instantons). Due to the explicit infrared regularisation there are no gauge
field zero modes. The Dirac operator of instanton configurations shows a zero
mode even after the infrared regularisation, which leads to U_A(1)-violating
terms in the effective action. These terms are calculated in the limit of large
scales k.Comment: 22 pages, latex, no figures, with stylistic changes and some
arguments streamlined, typos corrected, References added, to appear in Phys.
Rev.
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