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

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, $E_{GZK} \simeq 4 \times 10^{19} eV$, 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

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