499 research outputs found
Magnetic component of Yang-Mills plasma
Confinement in non-Abelian gauge theories is commonly ascribed to percolation
of magnetic monopoles, or strings in the vacuum. At the deconfinement phase
transition the condensed magnetic degrees of freedom are released into gluon
plasma as thermal magnetic monopoles. We point out that within the percolation
picture lattice simulations can be used to estimate the monopole content of the
gluon plasma. We show that right above the critical temperature the monopole
density remains a constant function of temperature, as for a liquid, and then
grows, like for a gas.Comment: 4 pages, no figures; replaced to match published versio
High energy parton-parton amplitudes from lattice QCD and the stochastic vacuum model
Making use of the gluon gauge-invariant two-point correlation function,
recently determined by numerical simulation on the lattice in the quenched
approximation and the stochastic vacuum model, we calculate the elementary
(parton-parton) amplitudes in both impact-parameter and momentum transfer
spaces. The results are compared with those obtained from the Kr\"{a}mer and
Dosch ansatz for the correlators. Our main conclusion is that the divergences
in the correlations functions suggested by the lattice calculations do not
affect substantially the elementary amplitudes. Phenomenological and
semiempirical information presently available on elementary amplitudes is also
referred to and is critically discussed in connection with some theoretical
issues.Comment: Text with 11 pages in LaTeX (twocolumn form), 10 figures in
PostScript (psfig.tex used). Replaced with changes, Fig.1 modified, two
references added, some points clarified, various typos corrected. Version to
appear in Phys. Rev.
Planar Drawings of Fixed-Mobile Bigraphs
A fixed-mobile bigraph G is a bipartite graph such that the vertices of one
partition set are given with fixed positions in the plane and the mobile
vertices of the other part, together with the edges, must be added to the
drawing. We assume that G is planar and study the problem of finding, for a
given k >= 0, a planar poly-line drawing of G with at most k bends per edge. In
the most general case, we show NP-hardness. For k=0 and under additional
constraints on the positions of the fixed or mobile vertices, we either prove
that the problem is polynomial-time solvable or prove that it belongs to NP.
Finally, we present a polynomial-time testing algorithm for a certain type of
"layered" 1-bend drawings
The 2-dimensional non-linear sigma-model on a random latice
The O(n) non-linear -model is simulated on 2-dimensional regular and
random lattices. We use two different levels of randomness in the construction
of the random lattices and give a detailed explanation of the geometry of such
lattices. In the simulations, we calculate the mass gap for and 8,
analysing the asymptotic scaling of the data and computing the ratio of Lambda
parameters . These ratios are in
agreement with previous semi-analytical calculations. We also numerically
calculate the topological susceptibility by using the cooling method.Comment: REVTeX file, 23 pages. 13 postscript figures in a separate compressed
tar fil
Non-Perturbative Scales in Soft Hadronic Collisions at High Energies
We investigate the role of nonperturbative quark-gluon dynamics in soft high
energy processes. In order to reproduce differential and total cross sections
for elastic proton-proton and proton-antiproton-scattering at high energy and
small momentum transfer it turns out that we need two scales, the gluonic
correlation length and a confinement scale. We find a small gluonic correlation
length, a = 0.2 fm, in accordance with recent lattice QCD results.Comment: 8 pages,latex, 2 figures uuencode
On Smooth Orthogonal and Octilinear Drawings: Relations, Complexity and Kandinsky Drawings
We study two variants of the well-known orthogonal drawing model: (i) the
smooth orthogonal, and (ii) the octilinear. Both models form an extension of
the orthogonal, by supporting one additional type of edge segments (circular
arcs and diagonal segments, respectively).
For planar graphs of max-degree 4, we analyze relationships between the graph
classes that can be drawn bendless in the two models and we also prove
NP-hardness for a restricted version of the bendless drawing problem for both
models. For planar graphs of higher degree, we present an algorithm that
produces bi-monotone smooth orthogonal drawings with at most two segments per
edge, which also guarantees a linear number of edges with exactly one segment.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
Asymptotic Energy Dependence of Hadronic Total Cross Sections from Lattice QCD
The nonperturbative approach to soft high-energy hadron-hadron scattering,
based on the analytic continuation of Wilson-loop correlation functions from
Euclidean to Minkowskian theory, allows to investigate the asymptotic energy
dependence of hadron-hadron total cross sections in lattice QCD. In this paper
we will show, using best fits of the lattice data with proper functional forms
satisfying unitarity and other physical constraints, how indications emerge in
favor of a universal asymptotic high-energy behavior of the kind B log^2 s for
hadronic total cross sections.Comment: Revised and extended version; 29 pages, 4 figure
- âŠ