18,962 research outputs found
Spinning Relativistic Particle in an External Electromagnetic Field
The Hamiltonian formulation of the motion of a spinning relativistic particle
in an external electromagnetic field is considered. The approach is based on
the introduction of new coordinates and their conjugated momenta to describe
the spin degrees of freedom together with an appropriate set of constraints in
the Dirac formulation. For particles with gyromagnetic ratio , the
equations of motion do not predict any deviation from the standard Lorentz
force, while for an additional force, which corresponds to the
magnetic dipole force, is obtained.Comment: Latex file, 11 page
Cross-correlation of the CMB and radio galaxies in real, harmonic and wavelet spaces: detection of the integrated Sachs-Wolfe effect and dark energy constraints
We report the first detection of the ISW effect in wavelet space, at scales
in the sky around 7 degrees with a significance of around 3.3 sigma, by
cross-correlating the WMAP first-year data and the NRAO VLA Sky Survey (NVSS).
In addition, we present a detailed comparison among the capabilities of three
different techniques for two different objectives: to detect the ISW and to put
constraints in the nature of the dark energy. The three studied techniques are:
the cross-angular power spectrum (CAPS, harmonic space), the correlation
function (CCF, real space) and the covariance of the Spherical Mexican Hat
Wavelet (SMHW) coefficients (CSMHW, wavelet space). We prove that the CSMHW is
expected to provide a higher detection of the ISW effect for a certain scale.
This prediction has been corroborated by the analysis of the data. The SMHW
analysis shows that the cross-correlation signal is caused neither by
systematic effects nor foreground contamination. However, by taking into
account the information encoded in all the multipoles/scales/angles, the CAPS
provides slightly better constraints than the SMHW in the cosmological
parameters that define the nature of the dark energy. The limits provided by
the CCF are wider than for the other two methods. Two different cases have been
studied: 1) a flat Lambda-CDM universe and 2) a flat universe with an equation
of state parameter different from -1. In the first case, the CAPS provides (for
a bias value of b = 1.6) 0.59 < Lambda density < 0.84 (at 1 sigma CL).
Moreover, the CAPS rejects the range Lambda density < 0.1 at 3.5 sigma, which
is the highest detection of the dark energy reported up to date. In the second
case, the CAPS gives 0.50 < dark energy density < 0.82 and -1.16 < w < 0.43 (at
1 sigma CL).Comment: 12 pages, 7 figures, accepted for publication in MNRAS. Analysis
redone. Changes in the estimation of the cosmological parametres. Additional
comparison between wavelets and more standard technique
The demand for urban transport: An application of discrete choice model for Cadiz
The study of the demand for transport has among others applications, the valuation of travel time saving that is a very important question in cost-benefit analysis, and to adopt transport policy tools. Since McFadden developed a discrete choice model for travel demand, it has usually been the application of this model to study the individual behaviour when he has to choice among transport modes. Citizens of big cities have to face traffic congestion; pollution, wasted time in travels and fuel, noise, stress and accidents are the costs imposed by congestion to society, elements that reduce the quality of life in cities. Public transport is a real alternative to private transport that is socially less expensive, for this reason this paper tries to forecast travel demand for public transport in Cadiz when travelling have to choice between public or private transport, using a discrete choice model. The results of this analysis (travel demand, value of time, elasticities) can be used to design transport policies that could reduce congestion.
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