13,532 research outputs found
The scattering map in two coupled piecewise-smooth systems, with numerical application to rocking blocks
We consider a non-autonomous dynamical system formed by coupling two
piecewise-smooth systems in \RR^2 through a non-autonomous periodic
perturbation. We study the dynamics around one of the heteroclinic orbits of
one of the piecewise-smooth systems. In the unperturbed case, the system
possesses two normally hyperbolic invariant manifolds of dimension two
with a couple of three dimensional heteroclinic manifolds between them. These
heteroclinic manifolds are foliated by heteroclinic connections between
tori located at the same energy levels. By means of the {\em impact map} we
prove the persistence of these objects under perturbation. In addition, we
provide sufficient conditions of the existence of transversal heteroclinic
intersections through the existence of simple zeros of Melnikov-like functions.
The heteroclinic manifolds allow us to define the {\em scattering map}, which
links asymptotic dynamics in the invariant manifolds through heteroclinic
connections. First order properties of this map provide sufficient conditions
for the asymptotic dynamics to be located in different energy levels in the
perturbed invariant manifolds. Hence we have an essential tool for the
construction of a heteroclinic skeleton which, when followed, can lead to the
existence of Arnol'd diffusion: trajectories that, on large time scales,
destabilize the system by further accumulating energy. We validate all the
theoretical results with detailed numerical computations of a mechanical system
with impacts, formed by the linkage of two rocking blocks with a spring
Shear-Free Gravitational Waves in an Anisotropic Universe
We study gravitational waves propagating through an anisotropic Bianchi I
dust-filled universe (containing the Einstein-de-Sitter universe as a special
case). The waves are modeled as small perturbations of this background
cosmological model and we choose a family of null hypersurfaces in this
space-time to act as the histories of the wavefronts of the radiation. We find
that the perturbations we generate can describe pure gravitational radiation if
and only if the null hypersurfaces are shear-free. We calculate the
gauge-invariant small perturbations explicitly in this case. How these differ
from the corresponding perturbations when the background space-time is
isotropic is clearly exhibited.Comment: 32 pages, accepted for publication in Physical Review
Inclusive production of the state in collisions at D0
We present a study of the inclusive production of the with the
decay to the final state in hadronic collisions. Based on
of collision data collected by the D0
experiment at the Fermilab Tevatron collider, we report the first evidence for
the prompt production of and find the fraction of events
originating from hadrons to be . The ratio of the non-prompt
production rate to the yield in the same channel is . The values of the
mass ~MeV
and width ~MeV are consistent with previous measurements. 8 pages, 2 figuesComment: Submitted to PRL. * pages, 2 figure
Precise measurement of the top quark mass in dilepton decays using optimized neutrino weighting
We measure the top quark mass in dilepton final states of top-antitop events
in proton-antiproton collisions at sqrt(s) = 1.96 TeV, using data corresponding
to an integrated luminosity of 9.7 fb^-1 at the Fermilab Tevatron Collider. The
analysis features a comprehensive optimization of the neutrino weighting method
to minimize the statistical uncertainties. We also improve the calibration of
jet energies using the calibration determined in top-antitop to lepton+jets
events, which reduces the otherwise limiting systematic uncertainty from the
jet energy scale. The measured top quark mass is mt = 173.32 +/- 1.36(stat) +/-
0.85(syst) GeV.Comment: 10 pages, 2 figures, 2 tables, subm. to Phys. Lett.
Scales of the Extra Dimensions and their Gravitational Wave Backgrounds
Circumstances are described in which symmetry breaking during the formation
of our three-dimensional brane within a higher-dimensional space in the early
universe excites mesoscopic classical radion or brane-displacement degrees of
freedom and produces a detectable stochastic background of gravitational
radiation. The spectrum of the background is related to the unification energy
scale and the the sizes and numbers of large extra dimensions. It is shown that
properties of the background observable by gravitational-wave observatories at
frequencies Hz to Hz contain information about
unification on energy scales from 1 to TeV, gravity propagating
through extra-dimension sizes from 1 mm to mm, and the dynamical
history and stabilization of from one to seven extra dimensions.Comment: 6 pages, Latex, 1 figure, submitted to Phys. Re
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