315 research outputs found
Fluctuations and the QCD phase diagram
In this contribution the role of quantum fluctuations for the QCD phase
diagram is discussed. This concerns in particular the importance of the matter
back-reaction to the gluonic sector. The impact of these fluctuations on the
location of the confinement/deconfinement and the chiral transition lines as
well as their interrelation are investigated. Consequences of our findings for
the size of a possible quarkyonic phase and location of a critical endpoint in
the phase diagram are drawn.Comment: 7 pages, 3 figures, to appear in Physics of Atomic Nucle
On the ground states of the Bernasconi model
The ground states of the Bernasconi model are binary +1/-1 sequences of
length N with low autocorrelations. We introduce the notion of perfect
sequences, binary sequences with one-valued off-peak correlations of minimum
amount. If they exist, they are ground states. Using results from the
mathematical theory of cyclic difference sets, we specify all values of N for
which perfect sequences do exist and how to construct them. For other values of
N, we investigate almost perfect sequences, i.e. sequences with two-valued
off-peak correlations of minimum amount. Numerical and analytical results
support the conjecture that almost perfect sequences do exist for all values of
N, but that they are not always ground states. We present a construction for
low-energy configurations that works if N is the product of two odd primes.Comment: 12 pages, LaTeX2e; extended content, added references; submitted to
J.Phys.
Tree-based Coarsening and Partitioning of Complex Networks
Many applications produce massive complex networks whose analysis would
benefit from parallel processing. Parallel algorithms, in turn, often require a
suitable network partition. For solving optimization tasks such as graph
partitioning on large networks, multilevel methods are preferred in practice.
Yet, complex networks pose challenges to established multilevel algorithms, in
particular to their coarsening phase.
One way to specify a (recursive) coarsening of a graph is to rate its edges
and then contract the edges as prioritized by the rating. In this paper we (i)
define weights for the edges of a network that express the edges' importance
for connectivity, (ii) compute a minimum weight spanning tree with
respect to these weights, and (iii) rate the network edges based on the
conductance values of 's fundamental cuts. To this end, we also (iv)
develop the first optimal linear-time algorithm to compute the conductance
values of \emph{all} fundamental cuts of a given spanning tree. We integrate
the new edge rating into a leading multilevel graph partitioner and equip the
latter with a new greedy postprocessing for optimizing the maximum
communication volume (MCV). Experiments on bipartitioning frequently used
benchmark networks show that the postprocessing already reduces MCV by 11.3%.
Our new edge rating further reduces MCV by 10.3% compared to the previously
best rating with the postprocessing in place for both ratings. In total, with a
modest increase in running time, our new approach reduces the MCV of complex
network partitions by 20.4%
Twistfield Perturbations of Vertex Operators in the Z_2-Orbifold Model
We apply Kadanoff's theory of marginal deformations of conformal field
theories to twistfield deformations of Z_2 orbifold models in K3 moduli space.
These deformations lead away from the Z_2 orbifold sub-moduli-space and hence
help to explore conformal field theories which have not yet been understood. In
particular, we calculate the deformation of the conformal dimensions of vertex
operators for p^2<1 in second order perturbation theory.Comment: Latex2e, 19 pages, 1 figur
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
Optimal Traffic Networks
Inspired by studies on the airports' network and the physical Internet, we
propose a general model of weighted networks via an optimization principle. The
topology of the optimal network turns out to be a spanning tree that minimizes
a combination of topological and metric quantities. It is characterized by a
strongly heterogeneous traffic, non-trivial correlations between distance and
traffic and a broadly distributed centrality. A clear spatial hierarchical
organization, with local hubs distributing traffic in smaller regions, emerges
as a result of the optimization. Varying the parameters of the cost function,
different classes of trees are recovered, including in particular the minimum
spanning tree and the shortest path tree. These results suggest that a
variational approach represents an alternative and possibly very meaningful
path to the study of the structure of complex weighted networks.Comment: 4 pages, 4 figures, final revised versio
Doing audio-visual montage to explore time and space: The everyday rhythms of Billingsgate Fish Market
This article documents, shows and analyses the everyday rhythms of Billingsgate, London’s wholesale fish market. It takes the form of a short film based an audio-visual montage of time-lapse photography and sound recordings, and a textual account of the dimensions of market life revealed by this montage. Inspired by Henri Lefebvre’s Rhythmanalysis, and the embodied experience of moving through and sensing the market, the film renders the elusive quality of the market and the work that takes place within it to make it happen. The composite of audio-visual recordings immerses viewers in the space and atmosphere of the market and allows us to perceive and analyse rhythms, patterns, flows, interactions, temporalities and interconnections of market work, themes that this article discusses. The film is thereby both a means of showing market life and an analytic tool for making sense of it. This article critically considers the documentation, evocation and analysis of time and space in this way
On the Convergence of the Expansion of Renormalization Group Flow Equation
We compare and discuss the dependence of a polynomial truncation of the
effective potential used to solve exact renormalization group flow equation for
a model with fermionic interaction (linear sigma model) with a grid solution.
The sensitivity of the results on the underlying cutoff function is discussed.
We explore the validity of the expansion method for second and first-order
phase transitions.Comment: 12 pages with 10 EPS figures included; revised versio
Connection between Chiral Symmetry Restoration and Deconfinement
We propose a simple explanation for the connection between chiral symmetry
restoration and deconfinement in QCD at high temperature. In the Higgs
description of the QCD vacuum both spontaneous chiral symmetry breaking and
effective gluon masses are generated by the condensate of a color octet
quark-antiquark pair. The transition to the high temperature state proceeds by
the melting of this condensate. Quarks and gluons become (approximately)
massless at the same critical temperature. For instanton-dominated effective
multiquark interactions and three light quarks with equal mass we find a first
order phase transition at a critical temperature around 170 MeV.Comment: New section on vortices,33 pages,LaTe
Methodological entanglements in the field: Methods, transitions and transmissions
While much discussion of art practice within research and university contexts tends to draw from 'practice-led' or 'practice-based' research, those practices outside the visual arts that deploy art-related methods and techniques often sit uncomfortably within other disciplines and struggle to be accounted for within official university accountabilities. This situation creates a divide between visual art accountable practices and those that do not fit. It is the latter category we wish to explore. As ethnographic researchers within cultural studies and sociology, the process of making and thinking through art-based methods is an integral part of doing research. Through the interdisciplinary process we seek to explore overlaps between traditional and non-traditional modes of making, presenting and transmitting knowledge to audiences
- …