257 research outputs found
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
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
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.
Dirac Operators and the Calculation of the Connes Metric on arbitrary (Infinite) Graphs
As an outgrowth of our investigation of non-regular spaces within the context
of quantum gravity and non-commutative geometry, we develop a graph Hilbert
space framework on arbitrary (infinite) graphs and use it to study spectral
properties of graph-Laplacians and graph-Dirac-operators. We define a spectral
triplet sharing most of the properties of what Connes calls a spectral triple.
With the help of this scheme we derive an explicit expression for the
Connes-distance function on general directed or undirected graphs. We derive a
series of apriori estimates and calculate it for a variety of examples of
graphs. As a possibly interesting aside, we show that the natural setting of
approaching such problems may be the framework of (non-)linear programming or
optimization. We compare our results (arrived at within our particular
framework) with the results of other authors and show that the seeming
differences depend on the use of different graph-geometries and/or Dirac
operators.Comment: 27 pages, Latex, comlementary to an earlier paper, general treatment
of directed and undirected graphs, in section 4 a series of general results
and estimates concerning the Connes Distance on graphs together with examples
and numerical estimate
- …