2,004 research outputs found
Threshold Effects and Lorentz Symmetry
Evidence on the violation of Lorentz symmetry arises from the observation of
cosmic rays with energies beyond the GZK cutoff, , from the apparent transparency of the Universe to the propagation
of high energy gamma radiation and from the stability of pions in air showers.
These three paradoxes can be explained through deformations of the relativistic
dispersion relation. Theoretical ideas aimed to understand how Lorentz symmetry
may be broken and phenomenologically interesting deformations of the
relativistic dispersion relation may arise are briefly discussed.Comment: 7 pages. Talk presented at the ``Decoherence, Information, Complexity
and Entropy 2002'', Piombino, Italy, September 200
Quantum and Classical divide: the gravitational case
We study the transition between quantum and classical behavior of particles
in a gravitational quantum well. We analyze how an increase in the particles
mass turns the energy spectrum into a continuous one, from an experimental
point of view. We also discuss the way these effects could be tested by
conducting experiments with atoms and fullerene-type molecules.Comment: Revtex4, 5 pages, 2 figures; version to appear in Physics Letters
Dark Energy - Dark Matter Unification: Generalized Chaplygin Gas Model
We review the main features of the generalized Chaplygin gas (GCG) proposal
for unification of dark energy and dark matter and discuss how it admits an
unique decomposition into dark energy and dark matter components once
phantom-like dark energy is excluded. In the context of this approach we
consider structure formation and show that unphysical oscillations or blow-up
in the matter power spectrum are not present. Moreover, we demonstrate that the
dominance of dark energy occurs about the time when energy density fluctuations
start evolving away from the linear regime.Comment: 15 pages, 5 figures; Talk presented at the V New Worlds in
Astroparticle Physics, Faro, Portugal, 8-10 January 2005. Reference and
numbering of equations fixe
Cosmological thinking: cultural heritage and challenge
The limitations of current technology do not allow one to foresee the
expansion of the humankind beyond our planet for at least a few decades.
Furthermore, the laws of physics, as for as they are known, preclude any form
of traveling beyond the speed of light, as well as any viable and stable
space-time shortcuts (wormholes, warp-drives, etc) that would facilitate cosmic
traveling. Given the vastness of the Universe these are insurmountable
obstacles for any {\it in situ} exploration of the cosmos beyond our most
immediate cosmic neighbourhood. Nevertheless, the Universe is transparent and
contains countless sources of visible light. Actually, in the last decades,
technological developments have made possible to observe the cosmos throughout
most of the electromagnetic spectrum as well as to perform dynamical studies
that allow perceiving the presence of invisible components such as black holes,
dark matter and dark energy. In this respect, humankind has then been given the
opportunity to unravel the inner workings of the cosmos and through this
process be part of the cosmic habitat. In this contribution various forms of
cosmological thinking will be discussed, from some myths of creation till some
of the latest scientific discoveries.Comment: 18 pages, 2 figures. Talk delivered at the Third International
Symposium "Fronteiras da Ci\^encia: A Humanidade e o Cosmos", 13 - 14
November 2009, Universidade Fernando Pesssoa, Oporto, Portuga
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