29,869 research outputs found
Scattering approach to fidelity decay in closed systems and parametric level correlations
This paper is based on recent work which provided an exact analytical
description of scattering fidelity experiments with a microwave cavity under
the variation of an antenna coupling [K\"ober et al., Phys. Rev. E 82, 036207
(2010)]. It is shown that this description can also be used to predict the
decay of the fidelity amplitude for arbitrary Hermitian perturbations of a
closed system. Two applications are presented: First, the known result for
global perturbations is re-derived, and second, the exact analytical expression
for the perturbation due to a moving S-wave scatterer is worked out. The latter
is compared to measured data from microwave experiments, which have been
reported some time ago. Finally, we generalize an important relation between
fidelity decay and parametric level correlations to arbitrary perturbations.Comment: 20 pages, 2 figures, research article, (v2: stylistic changes, ref.
added
CP violation in semileptonic tau lepton decays
The leading order contribution to the direct CP asymmetry in tau^{+/-} ->
K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The
weak phase required for CP violation is introduced through an interesting
mechanism involving second order weak interactions, which is also responsible
for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The
calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large
window for studying effects of non-standard sources of CP violation in this
observable.Comment: 5 pages, 3 figures, version published in Phys.Rev.
Generalizing the relativistic quantization condition to include all three-pion isospin channels
We present a generalization of the relativistic, finite-volume,
three-particle quantization condition for non-identical pions in isosymmetric
QCD. The resulting formalism allows one to use discrete finite-volume energies,
determined using lattice QCD, to constrain scattering amplitudes for all
possible values of two- and three-pion isospin. As for the case of identical
pions considered previously, the result splits into two steps: The first
defines a non-perturbative function with roots equal to the allowed energies,
, in a given cubic volume with side-length . This function depends
on an intermediate three-body quantity, denoted ,
which can thus be constrained from lattice QCD input. The second step is a set
of integral equations relating to the physical
scattering amplitude, . Both of the key relations, and
, are shown to be
block-diagonal in the basis of definite three-pion isospin, ,
so that one in fact recovers four independent relations, corresponding to
. We also provide the generalized threshold expansion
of for all channels, as well as parameterizations
for all three-pion resonances present for and
. As an example of the utility of the generalized formalism,
we present a toy implementation of the quantization condition for
, focusing on the quantum numbers of the and
resonances.Comment: 46 pages, 4 figures. Updated to match erratum published in JHEP. Main
conclusions and results unchange
Understanding co-operative R&D activity: evidence from four European countries
This paper investigates co-operative research activity by firms using data from
the 3rd Community Innovation Survey for four countries, France, Germany, Spain and the
UK. We build on the Cassiman and Veugelers (CV) (2002) study of Belgian manufacturing
firms, by incorporating information on the service sector, and considering the role of public
support in affecting firms’ decisions to co-operate. Our results support those in CV, in that
we find a positive relationship between the likelihood of undertaking co-operative R&D
and both incoming knowledge spillovers and the extent to which firms find strategic
methods important in appropriating the returns to innovative activity. We find that public
support is positively related to the probability of undertaking co-operative agreements
particularly with regard to the likelihood of co-operation with the research base. We find
some evidence, in particular for Spain, that firms carry out co-operative R&D to overcome
excessive perceived risks and financial constraints
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