586 research outputs found
Absorption and Direct Processes in Chaotic Wave Scattering
Recent results on the scattering of waves by chaotic systems with losses and
direct processes are discussed. We start by showing the results without direct
processes nor absorption. We then discuss systems with direct processes and
lossy systems separately. Finally the discussion of systems with both direct
processes and loses is given. We will see how the regimes of strong and weak
absorption are modified by the presence of the direct processes.Comment: 8 pages, 4 figures, Condensed Matter Physics (IV Mexican Meeting on
Mathematical and Experimental Physics), Edited by M. Martinez-Mares and J. A.
Moreno-Raz
Long-distance radiative corrections to the di-pion tau lepton decay
We evaluate the model-dependent piece of O(alpha) long-distance radiative
corrections to tau^- \to \pi^- \pi^0\nu_{\tau} decays by using a meson
dominance model. We find that these corrections to the di-pion invariant mass
spectrum are smaller than in previous calculations based on chiral perturbation
theory. The corresponding correction to the photon inclusive rate is tiny
(-0.15%) but it can be of relevance when new measurements reach better
precision.Comment: 4 pages, 2 figures. An estimate of the shift produced in the
evaluation of the h.v.p. contribution to the muon anomalous magnetic moment
is added. Version to appear in Phys. Rev.
Scattering of Elastic Waves in a Quasi-one-dimensional Cavity: Theory and Experiment
We study the scattering of torsional waves through a quasi-one-dimensional
cavity both, from the experimental and theoretical points of view. The
experiment consists of an elastic rod with square cross section. In order to
form a cavity, a notch at a certain distance of one end of the rod was grooved.
To absorb the waves, at the other side of the rod, a wedge, covered by an
absorbing foam, was machined. In the theoretical description, the scattering
matrix S of the torsional waves was obtained. The distribution of S is given by
Poisson's kernel. The theoretical predictions show an excellent agreement with
the experimental results. This experiment corresponds, in quantum mechanics, to
the scattering by a delta potential, in one dimension, located at a certain
distance from an impenetrable wall
Electromagnetic prompt response in an elastic wave cavity
A rapid, or prompt response, of an electromagnetic nature, is found in an
elastic wave scattering experiment. The experiment is performed with torsional
elastic waves in a quasi-one-dimensional cavity with one port, formed by a
notch grooved at a certain distance from the free end of a beam. The stationary
patterns are diminished using a passive vibration isolation system at the other
end of the beam. The measurement of the resonances is performed with
non-contact electromagnetic-acoustic transducers outside the cavity. In the
Argand plane, each resonance describes a circle over a base impedance curve
which comes from the electromagnetic components of the equipment. A model,
based on a variation of Poisson's kernel is developed. Excellent agreement
between theory and experiment is obtained.Comment: 4 pages, 5 figure
Experimental determination of the absorption strength in absorbing chaotic cavities
Due to the experimental necessity we present a formula to determine the
absorption strength by power losses inside a chaotic system (cavities, graphs,
acoustic resonators, etc) when the antenna coupling, always present in
experimental measurements, is taken into account. This is done by calculating
the average of the absorption coefficient as a function of the absorption
strength and the coupling of the antenna to the system, in the one channel
case.Comment: 6 pages, 3 figures, Submitted to Phys. Rev.
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