Search results for "relativitat"
showing 10 items of 20 documents
Search for neutral Higgs bosons decaying into four taus at LEP2
2010
A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb-1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, β2 = σ(e+e -→Zh)/σSM(e+e-→Zh) ×B(h→aa)×B(a→τ+τ-) 2. For mh 1 is excluded at the 95% confidence level.
Creatable universes
2007
We consider the question of properly defining energy and momenta for non asymptotic Minkowskian spaces in general relativity. Only spaces of this type, whose energy, linear 3-momentum, and intrinsic angular momentum vanish, would be candidates for creatable universes, that is, for universes which could have arisen from a vacuum quantum fluctuation. Given a universe, we completely characterize the family of coordinate systems for which one could sensibly say that this universe is a creatable universe.
Precision measurement of D meson mass differences
2013
Using three- and four-body decays of D mesons produced in semileptonic b-hadron decays, precision measurements of D meson mass differences are made together with a measurement of the D-0 mass. The measurements are based on a dataset corresponding to an integrated luminosity of 1.0 fb(-1) collected in pp collisions at 7 TeV. Using the decay D-0 -> K+K-K-pi(+), the D-0 mass is measured to be M(D-0) = 1864.75 +/- 0.15 (stat) +/- 0.11 (syst) MeV/c(2). The mass differences M(D+) - M(D-0) = 4.76 +/- 0.12 (stat) +/- 0.07 (syst) MeV/c(2), M(D-s(+)) - M(D+) = 98.68 +/- 0.03 (stat) +/- 0.04 (syst) MeV/c(2) are measured using the D-0 -> K+K-pi(+)pi(-) and D-(s)(+) -> K+K-pi(+) modes.
Implicaciones de la evolución histórica de algunos conceptos en la enseñanza de la Relatividad
2006
La relatividad es una parte importante de la fisica moderna. En este articulo se analiza el debate en torno a la utilizacion de la historia de la ciencia para orientar la didactica de la relatividad en la ensenanza secundaria. Se repasa la evolucion historica de algunos conceptos clave de la relatividad especial y se muestra su implicacion en la ensenanza-aprendizaje.Palabras clave: ensenanza-aprendizaje; relatividad; historia de la ciencia.Implications of the historical evolution of some concepts in the teaching of relativityThe relativity is an important part the modern physics. In this article we analyze the discussion around the use of the history of science to guide the didactics of th…
Two-Perfect Fluid Interpretation of an Energy Tensor
1990
The paper contains the necessary and sufficient conditions for a given energy tensor to be interpreted as a sum of two perfect fluids. Given a tensor of this class, the decomposition in two perfect fluids (which is determined up to a couple of real functions) is obtained.
On the uniqueness of the space-time energy in General Relativity. The illuminating case of the Schwarzschild metric
2013
The case of asymptotic Minkowskian space-times is considered. A special class of asymptotic rectilinear coordinates at the spatial infinity, related to a specific system of free falling observers, is chosen. This choice is applied in particular to the Schwarzschild metric, obtaining a vanishing energy for this space-time. This result is compared with the result of some known theorems on the uniqueness of the energy of any asymptotic Minkowskian space, showing that there is no contradiction between both results, the differences becoming from the use of coordinates with different operational meanings. The suitability of Gauss coordinates when defining an {\em intrinsic} energy is considered a…
Method to obtain shear-free two-fluid solutions of Einstein's equations.
1989
We use the Einstein equations, stated as an initial-value problem (3+1 formalism), to present a method for obtaining a class of solutions which may be interpreted as the gravitational field produced by a mixture of two perfect fluids. The four-velocity of one of the components is assumed to be a shear-free, irrotational, and geodesic vector field. The solutions are given up to a set of a hyperbolic quasilinear system.
Cosmic censorship conjecture in some matching spherical collapsing metrics
2017
A physically plausible Lema{\^{\i}}tre-Tolman-Bondi collapse in the marginally bound case is considered. By "physically plausible" we mean that the corresponding metric is ${\cal C}^1$ matched at the collapsing star surface and further that its {\em intrinsic} energy is, as due, stationary and finite. It is proved for this Lema{\^{\i}}tre-Tolman-Bondi collapse, for some parameter values, that its intrinsic central singularity is globally naked, thus violating the cosmic censorship conjecture with, for each direction, one photon, or perhaps a pencil of photons, leaving the singularity and reaching the null infinity. Our result is discussed in relation to some other cases in the current liter…
Solutions of the Einstein field equations for a bounded and finite discontinuous source, and its generalization: Metric matching conditions and jumpi…
2019
We consider the metrics of the General Relativity, whose energy-momentum tensor has a bounded support where it is continuous except for a finite step across the corresponding boundary surface. As a consequence, the first derivative of the metric across this boundary could perhaps present a finite step too. However, we can assume that the metric is ${\cal C}^1$ class everywhere. In such a case, although the partial second derivatives of the metric exhibit finite (no Dirac $\delta$ functions) discontinuities, the Dirac $\delta$ functions will still appear in the conservation equation of the energy-momentum tensor. As a consequence, strictly speaking, the corresponding metric solutions of the …
Students' Understanding of the Special Theory of Relativity and Design for a Guided Visit to a Science Museum
2009
International audience; This paper describes the design of teaching materials that are used as learning tools in school visits to a science museum. An exhibition on the A century of the Special Theory of Relativity, in the Kutxaespacio Science Museum, in San Sebastian (Spain), was used to design a visit for first year engineering students at the university and assess the learning which was achieved. The first part of the paper presents the teaching sequence which was designed to build a bridge between formal teaching and the exhibition visit. The second part analyses the potential of the exhibition and the aforementioned teaching sequence to influence the students' knowledge of three aspect…