3,947 research outputs found
A simple model for the evolution of a non-Abelian cosmic string network
In this paper we present the results of numerical simulations intended to
study the behavior of non-Abelian cosmic strings networks. In particular we are
interested in discussing the variations in the asymptotic behavior of the
system as we variate the number of generators for the topological defects. A
simple model which should generate cosmic strings is presented and its lattice
discretization is discussed. The evolution of the generated cosmic string
networks is then studied for different values for the number of generators for
the topological defects. Scaling solution appears to be approached in most
cases and we present an argument to justify the lack of scaling for the
residual cases
Adaptive spectral identification techniques in presence of undetected non linearities
The standard procedure for detection of gravitational wave coalescing
binaries signals is based on Wiener filtering with an appropriate bank of
template filters. This is the optimal procedure in the hypothesis of addictive
Gaussian and stationary noise. We study the possibility of improving the
detection efficiency with a class of adaptive spectral identification
techniques, analyzing their effect in presence of non stationarities and
undetected non linearities in the noiseComment: 4 pages, 2 figures, uses ws-procs9x6.cls Proceedings of "Non linear
physics: theory and experiment. II", Gallipoli (Lecce), 200
Efficiency of different matrix inversion methods applied to Wilson fermions
We compare different conjugate gradient -- like matrix inversion methods (CG,
BiCGstab1 and BiCGstab2) employing for this purpose the compact lattice quantum
electrodynamics (QED) with Wilson fermions. The main goals of this
investigation are the CPU time efficiency of the methods as well as the
influence of machine precision on the reliability of (physical) results
especially close to the 'critical' line ~\kappa_c(\bt).Comment: 27 pages LaTeX (epsf), all figures include
The SU(3) deconfining phase transition with Symanzik action
We report on the determination of the deconfining temperature in SU(3) pure
gauge theory, using the Symanzik tree level improved action, on lattices of
size 3 x 12^3, 4 x 16^3, 5 x 20^3, 6 x24^3. We find that the asymptotic scaling
violation pattern is similar to the one observed using the Wilson action. We
conclude that the irrelevant operators do not affect, in the range of couplings
considered, the lattice beta function. An analysis based on an effective
coupling formulation shows an apparent improvement.Comment: 8 pages, report IFUP-TH 12/9
Effect of Improving the Lattice Gauge Action on QCD Topology
We use lattice topology as a laboratory to compare the Wilson action (WA)
with the Symanzik-Weisz (SW) action constructed from a combination of (1x1) and
(1x2) Wilson loops, and the estimate of the renormalization trajectory (RT)
from a renormalization group transformation (RGT) which also includes higher
representations of the (1x1) loop. Topological charges are computed using the
geometric (L\"uscher's) and plaquette methods on the uncooled lattice, and also
by using cooling to remove ultraviolet artifacts. We show that as the action
improves by approaching the RT, the topological charges for individual
configurations computed using these three methods become more highly
correlated, suggesting that artificial lattice renormalizations to the
topological susceptibility can be suppressed by improving the action.Comment: 4 pages, 4 figures, poster presented at LATTICE96(improvement
DNA methylation and differentiation in plants.
DNA methylation in plants appears to be a phenomenon more complex
than in animals both for site specifity and the possible occurrence of two types of DNA methyltransferases. As in animals, DNA methylation appears to play a role in plant gene expression and differentiation (though recently acquired evidence indicated a less immediate relationship); other suggested roles for DNA methylation include genomic imprinting, paramutation and, to some extent, the gene silencing phenomenon observed in transgenic plants. However, while results obtained in mouse strictly link the presence of an active DNA methyltransferase with normal embryogenesis, in plants only circumstantial evidence points to the involvement of this enzyme in carrot somatic embryogenesis. What appears puzzling is the observation that hypomethylating mutants of Arabidopsis thaliana show normal development and morphology. The involvement of DNA methylation in plastid development is also debated. Of some interest appears the occurrence in plant cells of inhibitors of DNA methyltransferase activity although their biological significance and chemical nature remain to be elucidated
The two-phase issue in the O(n) non-linear -model: A Monte Carlo study
We have performed a high statistics Monte Carlo simulation to investigate
whether the two-dimensional O(n) non-linear sigma models are asymptotically
free or they show a Kosterlitz- Thouless-like phase transition. We have
calculated the mass gap and the magnetic susceptibility in the O(8) model with
standard action and the O(3) model with Symanzik action. Our results for O(8)
support the asymptotic freedom scenario.Comment: 3 pgs. espcrc2.sty included. Talk presented at LATTICE96(other
models
The search for a stochastic background of gravitational waves
I give a short introduction about stochastic backgrounds of gravitational waves, discussing the detection methods used, current and foreseen results and activities. I comment about expectations triggered by the recent ïŹrst direct detection of gravitational waves
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