4,889 research outputs found
Subspaces of a para-quaternionic Hermitian vector space
Let be a para-quaternionic Hermitian structure on the real
vector space . By referring to the tensorial presentation , we
give an explicit description, from an affine and metric point of view, of main
classes of subspaces of which are invariantly defined with respect to the
structure group of and respectively
Quantum transitions and quantum entanglement from Dirac-like dynamics simulated by trapped ions
Quantum transition probabilities and quantum entanglement for two-qubit
states of a four level trapped ion quantum system are computed for
time-evolving ionic states driven by Jaynes-Cummings Hamiltonians with
interactions mapped onto a \mbox{SU}(2)\otimes \mbox{SU}(2) group structure.
Using the correspondence of the method of simulating a dimensional
Dirac-like Hamiltonian for bi-spinor particles into a single trapped ion, one
preliminarily obtains the analytical tools for describing ionic state
transition probabilities as a typical quantum oscillation feature. For
Dirac-like structures driven by generalized Poincar\'e classes of coupling
potentials, one also identifies the \mbox{SU}(2)\otimes \mbox{SU}(2) internal
degrees of freedom corresponding to intrinsic parity and spin polarization as
an adaptive platform for computing the quantum entanglement between the
internal quantum subsystems which define two-qubit ionic states. The obtained
quantum correlational content is then translated into the quantum entanglement
of two-qubit ionic states with quantum numbers related to the total angular
momentum and to its projection onto the direction of the trapping magnetic
field. Experimentally, the controllable parameters simulated by ion traps can
be mapped into a Dirac-like system in the presence of an electrostatic field
which, in this case, is associated to ionic carrier interactions. Besides
exhibiting a complete analytical profile for ionic quantum transitions and
quantum entanglement, our results indicate that carrier interactions actively
drive an overall suppression of the quantum entanglement.Comment: 27 pags, 5 fig
Gravitating multidefects from higher dimensions
Warped configurations admitting pairs of gravitating defects are analyzed.
After devising a general method for the construction of multidefects, specific
examples are presented in the case of higher-dimensional Einstein-Hilbert
gravity. The obtained profiles describe diverse physical situations such as
(topological) kink-antikink systems, pairs of non-topological solitons and
bound configurations of a kink and of a non-topological soliton. In all the
mentioned cases the geometry is always well behaved (all relevant curvature
invariants are regular) and tends to five-dimensional anti-de Sitter space-time
for large asymptotic values of the bulk coordinate. Particular classes of
solutions can be generalized to the framework where the gravity part of the
action includes, as a correction, the Euler-Gauss-Bonnet combination. After
scrutinizing the structure of the zero modes, the obtained results are compared
with conventional gravitating configurations containing a single topological
defect.Comment: 27 pages, 5 included figure
The Growth of Business Firms: Theoretical Framework and Empirical Evidence
We introduce a model of proportional growth to explain the distribution of
business firm growth rates. The model predicts that the distribution is
exponential in the central part and depicts an asymptotic power-law behavior in
the tails with an exponent 3. Because of data limitations, previous studies in
this field have been focusing exclusively on the Laplace shape of the body of
the distribution. In this article, we test the model at different levels of
aggregation in the economy, from products to firms to countries, and we find
that the model's predictions agree with empirical growth distributions and
size-variance relationships.Comment: 22 pages, 5 Postscript figures, uses revtex4. to be published in
Proc. Natl. Acad. Sci. (2005
A Generalized Preferential Attachment Model for Business Firms Growth Rates: I. Empirical Evidence
We introduce a model of proportional growth to explain the distribution
of business firm growth rates. The model predicts that is Laplace
in the central part and depicts an asymptotic power-law behavior in the tails
with an exponent . Because of data limitations, previous studies in
this field have been focusing exclusively on the Laplace shape of the body of
the distribution. We test the model at different levels of aggregation in the
economy, from products, to firms, to countries, and we find that the its
predictions are in good agreement with empirical evidence on both growth
distributions and size-variance relationships.Comment: 8 pages, 4 figure
Optimizing the Earth-LISA "rendez-vous"
We present a general survey of heliocentric LISA orbits, hoping it might help
in the exercise of rescoping the mission. We try to semi-analytically optimize
the orbital parameters in order to minimize the disturbances coming from the
Earth-LISA interaction. In a set of numerical simulations we include
nonautonomous perturbations and provide an estimate of Doppler shift and
breathing as a function of the trailing angle.Comment: 18 pages, 16 figures. Submitted on CQ
Deriving relativistic momentum and energy. II. Three-dimensional case
We generalise a recent derivation of the relativistic expressions for
momentum and kinetic energy from the one-dimensional to the three-dimensional
case.Comment: 7 page
On aspects of self-consistency in the Dyson-Schwinger approach to QED and \lambda (\phi^\star \phi)^2 theories
We investigate some aspects of the self-consistency in the Dyson-Schwinger
approach to both the QED and the self-interacting scalar field theories. We
prove that the set of the Dyson-Schwinger equations, together with the
Green-Ward-Takahashi identity, is equivalent to the analogous set of integral
equations studied in condensed matter, namely many-body perturbation theory,
where it is solved self-consistently and iteratively. In this framework, we
compute the non-perturbative solution of the gap equation for the
self-interacting scalar field theory.Comment: 9 pages, to appear on Phys. Rev.
Noise Measurement of Interacting Ferromagnetic Particles with High Resolution Hall Microprobes
We present our first experimental determination of the magnetic noise of a
superspinglass made of < 1 pico-liter frozen ferrofluid. The measurements were
performed with a local magnetic field sensor based on Hall microprobes operated
with the spinning current technique. The results obtained, though preliminary,
qualitatively agree with the theoretical predictions of Fluctuation-Dissipation
theorem (FDT) violation [1].Comment: 4pages, 2 figure
Supersymmetric Sum Rules for Electromagnetic Multipoles
We derive model independent, non-perturbative supersymmetric sum rules for
the magnetic and electric multipole moments of any theory with N=1
supersymmetry. We find that in any irreducible N=1 supermultiplet the diagonal
matrix elements of the l-multipole moments are completely fixed in terms of
their off-diagonal matrix elements and the diagonal (l-1)-multipole moments.Comment: 10 pages, plain Te
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