958 research outputs found
Scalar field in cosmology: Potential for isotropization and inflation
The important role of scalar field in cosmology was noticed by a number of
authors. Due to the fact that the scalar field possesses zero spin, it was
basically considered in isotropic cosmological models. If considered in an
anisotropic model, the linear scalar field does not lead to isotropization of
expansion process. One needs to introduce scalar field with nonlinear potential
for the isotropization process to take place. In this paper the general form of
scalar field potentials leading to the asymptotic isotropization in case of
Bianchi type-I cosmological model, and inflationary regime in case of isotropic
space-time is obtained. In doing so we solved both direct and inverse problem,
where by direct problem we mean to find metric functions and scalar field for
the given potential, whereas, the inverse problem means to find the potential
and scalar field for the given metric function. The scalar field potentials
leading to the inflation and isotropization were found both for harmonic and
proper synchronic time.Comment: 10 page
Noether gauge symmetry for gravity in Palatini formalism
In this study, we consider a flat Friedmann-Robertson-Walker (FRW) universe
in the context of Palatini theory of gravity. Using the dynamical
equivalence between gravity and scalar-tensor theories, we construct a
point Lagrangian in the flat FRW spacetime. Applying {\em Noether gauge
symmetry approach} for this Lagrangian we find out the form of
and the exact solution for cosmic scale factor. It is shown that the resulting
form of yield a power-law expansion for the scale factor of the
universe.Comment: 7 pagese, no figures; Published in Astrophysics & Space Science. Some
minor corrections have been mad
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
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