25,468 research outputs found
Inducing charges and currents from extra dimensions
In a particular variant of Kaluza-Klein theory, the so-called induced-matter
theory (IMT), it is shown that any configuration of matter may be geometrically
induced from a five-dimensional vacuum space. By using a similar approach we
show that any distribution of charges and currents may also be induced from a
five-dimensional vacuum space. Whereas in the case of IMT the geometry is
Riemannian and the fundamental equations are the five-dimensional Einstein
equations in vacuum, here we consider a Minkowskian geometry and the
five-dimensional Maxwell equations in vacuum.Comment: 8 pages. Accepted for publication in Modern Physics Letters
Homogeneous cosmologies and the Maupertuis-Jacobi principle
A recent work showing that homogeneous and isotropic cosmologies involving
scalar fields are equivalent to the geodesics of certain effective manifolds is
generalized to the non-minimally coupled and anisotropic cases. As the
Maupertuis-Jacobi principle in classical mechanics, such result permits us to
infer some dynamical properties of cosmological models from the geometry of the
associated effective manifolds, allowing us to go a step further in the study
of cosmological dynamics. By means of some explicit examples, we show how the
geometrical analysis can simplify considerably the dynamical analysis of
cosmological models.Comment: 5 page
xPand: An algorithm for perturbing homogeneous cosmologies
In this paper, we develop in detail a fully geometrical method for deriving
perturbation equations about a spatially homogeneous background. This method
relies on the 3+1 splitting of the background space-time and does not use any
particular set of coordinates: it is implemented in terms of geometrical
quantities only, using the tensor algebra package xTensor in the xAct
distribution along with the extension for perturbations xPert. Our algorithm
allows one to obtain the perturbation equations for all types of homogeneous
cosmologies, up to any order and in all possible gauges. As applications, we
recover the well-known perturbed Einstein equations for
Friedmann-Lemaitre-Robertson-Walker cosmologies up to second order and for
Bianchi I cosmologies at first order. This work paves the way to the study of
these models at higher order and to that of any other perturbed Bianchi
cosmologies, by circumventing the usually too cumbersome derivation of the
perturbed equations.Comment: 21 pages, 2 figure
A gauge theoretic approach to elasticity with microrotations
We formulate elasticity theory with microrotations using the framework of
gauge theories, which has been developed and successfully applied in various
areas of gravitation and cosmology. Following this approach, we demonstrate the
existence of particle-like solutions. Mathematically this is due to the fact
that our equations of motion are of Sine-Gordon type and thus have soliton type
solutions. Similar to Skyrmions and Kinks in classical field theory, we can
show explicitly that these solutions have a topological origin.Comment: 15 pages, 1 figure; revised and extended version, one extra page;
revised and extended versio
On general flux backgrounds with localized sources
We derive new consistency conditions for string compactifications with
generic fluxes (RR, NSNS, geometrical) and localized sources (D-branes,
NS-branes, KK-monopoles). The constraints are all related by string dualities
and share a common origin in M-theory. We also find new sources of
instabilities. We discuss the importance of these conditions for the
consistency of the effective action and for the study of interpolating
solutions between vacua.Comment: 29 pages, 2 figures, v2: published versio
A square-torsion modification of Einstein-Cartan theory
In the present paper we consider a theory of gravity in which not only
curvature but also torsion is explicitly present in the Lagrangian, both with
their own coupling constant. In particular, we discuss the couplings to Dirac
fields and spin fluids: in the case of Dirac fields, we discuss how in our
approach, the Dirac self-interactions depend on the coupling constant as a
parameter that may even make these non-linearities manifest at subatomic
scales, showing different applications according to the value of the parameter
we have assigned; in the case of spin fluids, we discuss FLRW cosmological
models arising from the proposed theory.Comment: 21 page
Applications of ISES for vegetation and land use
Remote sensing relative to applications involving vegetation cover and land use is reviewed to consider the potential benefits to the Earth Observing System (Eos) of a proposed Information Sciences Experiment System (ISES). The ISES concept has been proposed as an onboard experiment and computational resource to support advanced experiments and demonstrations in the information and earth sciences. Embedded in the concept is potential for relieving the data glut problem, enhancing capabilities to meet real-time needs of data users and in-situ researchers, and introducing emerging technology to Eos as the technology matures. These potential benefits are examined in the context of state-of-the-art research activities in image/data processing and management
- …