26,840 research outputs found
On Lorentz violation in scattering at finite temperature
Small violation of Lorentz and CPT symmetries may emerge in models unifying
gravity with other forces of nature. An extension of the standard model with
all possible terms that violate Lorentz and CPT symmetries are included. Here a
CPT-even non-minimal coupling term is added to the covariant derivative. This
leads to a new interaction term that breaks the Lorentz symmetry. Our main
objective is to calculate the cross section for the
scattering in order to
investigate any violation of Lorentz and/or CPT symmetry at finite temperature.
Thermo Field Dynamics formalism is used to consider finite temperature effects.Comment: 12 pages, 1 figure, accepted for publication in PL
A Flexible Implementation of a Matrix Laurent Series-Based 16-Point Fast Fourier and Hartley Transforms
This paper describes a flexible architecture for implementing a new fast
computation of the discrete Fourier and Hartley transforms, which is based on a
matrix Laurent series. The device calculates the transforms based on a single
bit selection operator. The hardware structure and synthesis are presented,
which handled a 16-point fast transform in 65 nsec, with a Xilinx SPARTAN 3E
device.Comment: 4 pages, 4 figures. IEEE VI Southern Programmable Logic Conference
201
Early appraisal of the fixation probability in directed networks
In evolutionary dynamics, the probability that a mutation spreads through the
whole population, having arisen in a single individual, is known as the
fixation probability. In general, it is not possible to find the fixation
probability analytically given the mutant's fitness and the topological
constraints that govern the spread of the mutation, so one resorts to
simulations instead. Depending on the topology in use, a great number of
evolutionary steps may be needed in each of the simulation events, particularly
in those that end with the population containing mutants only. We introduce two
techniques to accelerate the determination of the fixation probability. The
first one skips all evolutionary steps in which the number of mutants does not
change and thereby reduces the number of steps per simulation event
considerably. This technique is computationally advantageous for some of the
so-called layered networks. The second technique, which is not restricted to
layered networks, consists of aborting any simulation event in which the number
of mutants has grown beyond a certain threshold value, and counting that event
as having led to a total spread of the mutation. For large populations, and
regardless of the network's topology, we demonstrate, both analytically and by
means of simulations, that using a threshold of about 100 mutants leads to an
estimate of the fixation probability that deviates in no significant way from
that obtained from the full-fledged simulations. We have observed speedups of
two orders of magnitude for layered networks with 10000 nodes
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