4,853 research outputs found
Braneworlds, Conformal Fields and the Gravitons
We investigate the dynamics of Randall-Sundrum AdS5 braneworlds with
5-dimensional conformal matter fields. In the scenario with a compact fifth
dimension the class of conformal fields with weight -4 is associated with exact
5-dimensional warped geometries which are stable under radion field
perturbations and describe on the brane the dynamics of inhomogeneous dust,
generalized dark radiation and homogeneous polytropic dark energy. We analyse
the graviton mode flutuations around this class of background solutions and
determine their mass eigenvalues and wavefunctions from a Sturm-Liouville
problem. We show that the localization of gravity is not sharp enough for large
mass hierarchies to be generated. We also discuss the physical bounds imposed
by experiments in particle physics, in astrophysics and in precise measurements
of the low energy gravitational interaction.Comment: LaTeX, 9 pages, 2 figures. Based on talk given in the Second
International Conference on Quantum Theories and the Renormalization Group in
Gravity and Cosmology, CSIC and University of Barcelona, Barcelona, Spain,
11-15 July 2006. Submitted to be published in the Conference Proceedings, J.
Phys. A: Math. Ge
A higher quantum bound for the V\'ertesi-Bene-Bell-inequality and the role of POVMs regarding its threshold detection efficiency
Recently, V\'{e}rtesi and Bene [Phys. Rev. A. {\bf 82}, 062115 (2010)]
derived a two-qubit Bell inequality, , which they show to be maximally
violated only when more general positive operator valued measures (POVMs) are
used instead of the usual von Neumann measurements. Here we consider a general
parametrization for the three-element-POVM involved in the Bell test and obtain
a higher quantum bound for the -inequality. With a higher quantum
bound for , we investigate if there is an experimental setup that can
be used for observing that POVMs give higher violations in Bell tests based on
this inequality. We analyze the maximum errors supported by the inequality to
identify a source of entangled photons that can be used for the test. Then, we
study if POVMs are also relevant in the more realistic case that partially
entangled states are used in the experiment. Finally, we investigate which are
the required efficiencies of the -inequality, and the type of
measurements involved, for closing the detection loophole. We obtain that POVMs
allow for the lowest threshold detection efficiency, and that it is comparable
to the minimal (in the case of two-qubits) required detection efficiency of the
Clauser-Horne-Bell-inequality.Comment: 11 Pages, 16 Figure
Noncommutative Metafluid Dynamics
In this paper we define a noncommutative (NC) Metafluid Dynamics
\cite{Marmanis}. We applied the Dirac's quantization to the Metafluid Dynamics
on NC spaces. First class constraints were found which are the same obtained in
\cite{BJP}. The gauge covariant quantization of the non-linear equations of
fields on noncommutative spaces were studied. We have found the extended
Hamiltonian which leads to equations of motion in the gauge covariant form. In
addition, we show that a particular transformation \cite{Djemai} on the usual
classical phase space (CPS) leads to the same results as of the
-deformation with . Besides, we will shown that an additional
term is introduced into the dissipative force due the NC geometry. This is an
interesting feature due to the NC nature induced into model.Comment: 11 page
Interference and complementarity for two-photon hybrid entangled states
In this work we generate two-photon hybrid entangled states (HES), where the
polarization of one photon is entangled with the transverse spatial degree of
freedom of the second photon. The photon pair is created by parametric
down-conversion in a polarization-entangled state. A birefringent double-slit
couples the polarization and spatial degrees of freedom of these photons and
finally, suitable spatial and polarization projections generate the HES. We
investigate some interesting aspects of the two-photon hybrid interference, and
present this study in the context of the complementarity relation that exists
between the visibilities of the one- and two-photon interference patterns.Comment: 10 pages, 4 figures. Accepted in Physical Review
Ancient Amazonian populations left lasting impacts on forest structure
Amazonia contains a vast expanse of contiguous tropical forest and is influential in global carbon and hydrological cycles. Whether ancient Amazonia was highly disturbed or modestly impacted, and how ancient disturbances have shaped current forest ecosystem processes, is still under debate. Amazonian Dark Earths (ADEs), which are anthropic soil types with enriched nutrient levels, are one of the primary lines of evidence for ancient human presence and landscape modifications in settings that mostly lack stone structures and which are today covered by vegetation. We assessed the potential of using moderate spatial resolution optical satellite imagery to predict ADEs across the Amazon Basin. Maximum entropy modeling was used to develop a predictive model using locations of ADEs across the basin and satellite‐derived remotely sensed indices. Amazonian Dark Earth sites were predicted to be primarily along the main rivers and in eastern Amazonia. Amazonian Dark Earth sites, when compared with randomly selected forested sites located within 50 km of ADE sites, were less green canopies (lower normalized difference vegetation index) and had lower canopy water content. This difference was accentuated in two drought years, 2005 and 2010. This is contrary to our expectation that ADE sites would have nutrient‐rich soils that support trees with greener canopies and forests on ADE soils being more resilient to drought. Biomass and tree height were lower on ADE sites in comparison with randomly selected adjacent sites. Our results suggested that ADE‐related ancient human impact on the forest is measurable across the entirety of the 6 million km2 of Amazon Basin using remotely sensed data
Gauging the SU(2) Skyrme model
In this paper the SU(2) Skyrme model will be reformulated as a gauge theory
and the hidden symmetry will be investigated and explored in the energy
spectrum computation. To this end we purpose a new constraint conversion
scheme, based on the symplectic framework with the introduction of Wess-Zumino
(WZ) terms in an unambiguous way. It is a positive feature not present on the
BFFT constraint conversion. The Dirac's procedure for the first-class
constraints is employed to quantize this gauge invariant nonlinear system and
the energy spectrum is computed. The finding out shows the power of the
symplectic gauge-invariant formalism when compared with another constraint
conversion procedures present on the literature.Comment: revised version, to appear in Phys.Rev.
Hamiltonian symplectic embedding of the massive noncommutative U(1) Theory
We show that the massive noncommutative U(1) theory is embedded in a gauge
theory using an alternative systematic way, which is based on the symplectic
framework. The embedded Hamiltonian density is obtained after a finite number
of steps in the iterative symplectic process, oppositely to the result proposed
using the BFFT formalism. This alternative formalism of embedding shows how to
get a set of dynamically equivalent embedded Hamiltonian densities.Comment: 16 pages, no figures, revtex4, corrected version, references
additione
Critical temperature and the transition from quantum to classical order parameter fluctuations in the three-dimensional Heisenberg antiferromagnet
We present results of extensive quantum Monte Carlo simulations of the
three-dimensional (3D) S=1/2 Heisenberg antiferromagnet. Finite-size scaling of
the spin stiffness and the sublattice magnetization gives the critical
temperature Tc/J = 0.946 +/- 0.001. The critical behavior is consistent with
the classical 3D Heisenberg universality class, as expected. We discuss the
general nature of the transition from quantum mechanical to classical (thermal)
order parameter fluctuations at a continuous Tc > 0 phase transition.Comment: 5 pages, Revtex, 4 PostScript figures include
Multiple-spin coherence transfer in linear Ising spin chains and beyond: numerically-optimized pulses and experiments
We study multiple-spin coherence transfers in linear Ising spin chains with
nearest neighbor couplings. These constitute a model for efficient information
transfers in future quantum computing devices and for many multi-dimensional
experiments for the assignment of complex spectra in nuclear magnetic resonance
spectroscopy. We complement prior analytic techniques for multiple-spin
coherence transfers with a systematic numerical study where we obtain strong
evidence that a certain analytically-motivated family of restricted controls is
sufficient for time-optimality. In the case of a linear three-spin system,
additional evidence suggests that prior analytic pulse sequences using this
family of restricted controls are time-optimal even for arbitrary local
controls. In addition, we compare the pulse sequences for linear Ising spin
chains to pulse sequences for more realistic spin systems with additional
long-range couplings between non-adjacent spins. We experimentally implement
the derived pulse sequences in three and four spin systems and demonstrate that
they are applicable in realistic settings under relaxation and experimental
imperfections-in particular-by deriving broadband pulse sequences which are
robust with respect to frequency offsets.Comment: 11 page
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