8,875 research outputs found
Localizing gravity on thick branes: a solution for massive KK modes of the Schroedinger equation
We generate scalar thick brane configurations in a 5D Riemannian space time
which describes gravity coupled to a self-interacting scalar field. We also
show that 4D gravity can be localized on a thick brane which does not
necessarily respect Z_2-symmetry, generalizing several previous models based on
the Randall-Sundrum system and avoiding the restriction to orbifold geometries
as well as the introduction of the branes in the action by hand. We begin by
obtaining a smooth brane configuration that preserves 4D Poincar'e invariance
and violates reflection symmetry along the fifth dimension. The extra dimension
can have either compact or extended topology, depending on the values of the
parameters of the solution. In the non-compact case, our field configuration
represents a thick brane with positive energy density centered at y=c_2,
whereas in the compact case we get pairs of thick branes. We recast as well the
wave equations of the transverse traceless modes of the linear fluctuations of
the classical solution into a Schroedinger's equation form with a volcano
potential of finite bottom. We solve Schroedinger equation for the massless
zero mode m^2=0 and obtain a single bound wave function which represents a
stable 4D graviton and is free of tachyonic modes with m^2<0. We also get a
continuum spectrum of Kaluza-Klein (KK) states with m^2>0 that are suppressed
at y=c_2 and turn asymptotically into plane waves. We found a particular case
in which the Schroedinger equation can be solved for all m^2>0, giving us the
opportunity of studying analytically the massive modes of the spectrum of KK
excitations, a rare fact when considering thick brane configurations.Comment: 8 pages in latex. We corrected signs in the field equations, the
expressions for the scalar field and the self-interacting potential. Due to
the fact that no changes are introduced in the warp factor, the physics of
the system remains the sam
Robustness of bipartite Gaussian entangled beams propagating in lossy channels
Subtle quantum properties offer exciting new prospects in optical
communications. Quantum entanglement enables the secure exchange of
cryptographic keys and the distribution of quantum information by
teleportation. Entangled bright beams of light attract increasing interest for
such tasks, since they enable the employment of well-established classical
communications techniques. However, quantum resources are fragile and undergo
decoherence by interaction with the environment. The unavoidable losses in the
communication channel can lead to a complete destruction of useful quantum
properties -- the so-called "entanglement sudden death". We investigate the
precise conditions under which this phenomenon takes place for the simplest
case of two light beams and demonstrate how to produce states which are robust
against losses. Our study sheds new light on the intriguing properties of
quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic
Mass gap for gravity localized on Weyl thick branes
We study the properties of a previously found family of thick brane
configurations in a pure geometric Weyl integrable 5D space time, a
non-Riemannian generalization of Kaluza-Klein (KK) theory involving a geometric
scalar field. Thus the 5D theory describes gravity coupled to a
self-interacting scalar field which gives rise to the structure of the thick
branes. Analyzing the graviton spectrum for this class of models, we find that
a particularly interesting situation arises for a special case in which the 4D
graviton is separated from the KK gravitons by a mass gap. The corresponding
effective Schroedinger equation has a modified Poeschl-Teller potential and can
be solved exactly. Apart from the massless 4D graviton, it contains one massive
KK bound state, and the continuum spectrum of delocalized KK modes. We discuss
the mass hierarchy problem, and explicitly compute the corrections to Newton's
law in the thin brane limit.Comment: 6 pages in Revtex, no figures, journal version, significately revised
and extende
Disentanglement in Bipartite Continuous-Variable Systems
Entanglement in bipartite continuous-variable systems is investigated in the
presence of partial losses, such as those introduced by a realistic quantum
communication channel, e.g. by propagation in an optical fiber. We find that
entanglement can vanish completely for partial losses, in a situa- tion
reminiscent of so-called entanglement sudden death. Even states with extreme
squeezing may become separable after propagation in lossy channels. Having in
mind the potential applications of such entangled light beams to optical
communications, we investigate the conditions under which entanglement can
survive for all partial losses. Different loss scenarios are examined and we
derive criteria to test the robustness of entangled states. These criteria are
necessary and sufficient for Gaussian states. Our study provides a framework to
investigate the robustness of continuous-variable entanglement in more complex
multipartite systems.Comment: Phys. Rev. A (in press
Analytical results for a Bessel function times Legendre polynomials class integrals
When treating problems of vector diffraction in electromagnetic theory, the
evaluation of the integral involving Bessel and associated Legendre functions
is necessary. Here we present the analytical result for this integral that will
make unnecessary numerical quadrature techniques or localized approximations.
The solution is presented using the properties of the Bessel and associated
Legendre functions.Comment: 4 page
The era of big data: Genome-scale modelling meets machine learning
With omics data being generated at an unprecedented rate, genome-scale modelling has become pivotal in its organisation and analysis. However, machine learning methods have been gaining ground in cases where knowledge is insufficient to represent the mechanisms underlying such data or as a means for data curation prior to attempting mechanistic modelling. We discuss the latest advances in genome-scale modelling and the development of optimisation algorithms for network and error reduction, intracellular constraining and applications to strain design. We further review applications of supervised and unsupervised machine learning methods to omics datasets from microbial and mammalian cell systems and present efforts to harness the potential of both modelling approaches through hybrid modelling
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