8,676 research outputs found
Constraining differential renormalization in abelian gauge theories
We present a procedure of differential renormalization at the one loop level
which avoids introducing unnecessary renormalization constants and
automatically preserves abelian gauge invariance. The amplitudes are expressed
in terms of a basis of singular functions. The local terms appearing in the
renormalization of these functions are determined by requiring consistency with
the propagator equation. Previous results in abelian theories, with and without
supersymmetry, are discussed in this context.Comment: 13 pages, LaTeX. Some equations corrected and a reference added.
Complete ps paper also available at http://www-ftae.ugr.es/papiros.html or
ftp://ftae3.ugr.es/pub/rmt/ugft73.p
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Investor protection and corporate control
We argue that investor protection changes the relative importance of productivity and scale as drivers of corporate control transfers. Using a large sample of European firms we find that control transfers are more correlated with increasing profitability and less correlated with increasing size when investor protection is strong. This suggests that improving productivity is more important as a driver of acquisitions when investor protection is strong, and alleviating financial constraints or empire building are more important when investor protection is weak. Our evidence is consistent with the idea that good investor protection promotes a more productive use of corporate assets
Wave localization in strongly nonlinear Hertzian chains with mass defect
We investigate the dynamical response of a mass defect in a one-dimensional
non-loaded horizontal chain of identical spheres which interact via the
nonlinear Hertz potential. Our experiments show that the interaction of a
solitary wave with a light intruder excites localized mode. In agreement with
dimensional analysis, we find that the frequency of localized oscillations
exceeds the incident wave frequency spectrum and nonlinearly depends on the
size of the intruder and on the incident wave strength. The absence of tensile
stress between grains allows some gaps to open, which in turn induce a
significant enhancement of the oscillations amplitude. We performed numerical
simulations that precisely describe our observations without any adjusting
parameters.Comment: 4 pages, 5 figures, submitted for publicatio
Cooper pairs as bosons
Although BCS pairs of fermions are known not to obey Bose-Einstein (BE)
commutation relations nor BE statistics, we show how Cooper pairs (CPs),
whether the simple original ones or the CPs recently generalized in a many-body
Bethe-Salpeter approach, being clearly distinct from BCS pairs at least obey BE
statistics. Hence, contrary to widespread popular belief, CPs can undergo BE
condensation to account for superconductivity if charged, as well as for
neutral-atom fermion superfluidity where CPs, but uncharged, are also expected
to form.Comment: 8 pages, 2 figures, full biblio info adde
Entanglement assisted alignment of reference frames using a dense covariant coding
We present a procedure inspired by dense coding, which enables a highly
efficient transmission of information of a continuous nature. The procedure
requires the sender and the recipient to share a maximally entangled state. We
deal with the concrete problem of aligning reference frames or trihedra by
means of a quantum system. We find the optimal covariant measurement and
compute the corresponding average error, which has a remarkably simple close
form. The connection of this procedure with that of estimating unitary
transformations on qubits is briefly discussed.Comment: 4 pages, RevTeX, Version to appear in PR
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