16,214 research outputs found
Quantum cosmology and the accelerated Universe
The quantized Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) model minimally
coupled to a free massless scalar field is studied and interpreted in the
Bohm-de Broglie framework. We analyze the quantum bohmian trajectories
corresponding to a certain class of gaussian packets, solutions of the
Wheeler-DeWitt equation. We show that these bohmian trajectories undergo an
accelerated expansion in the middle of its evolution due to the presence of
quantum cosmological effects in this period. It is shown that the
luminosity-redshift relation in the quantum cosmological model can be made
close to the corresponding relation coming from the classical model suplemented
by a cosmological constant, for . In this way we have the posibility of
interpreting the present observations of high redshift supernovae as the
consequence of a quantum cosmological effect.Comment: Talk given at X Marcell Grossmann Meeting, Rio de Janeiro, 2003.
Added references and some minor typos correction
Zeeman splitting of shallow donors in GaN
The Zeeman splitting of the donor spectra in cubic- and hexagonal-GaN are
studied using an effective mass theory approach. Soft-core pseudopotentials
were used to describe the chemical shift of the different substitutional
dopants. The donor ground states calculated range from 29.5 to 33.7 meV, with
typically 1 meV higher binding in the hexagonal phase. Carbon is found to
produce the largest donor binding energy. The ionization levels and excited
states are in excellent agreement with Hall and optical measurements, and
suggest the presence of residual C in recent experiments.Comment: REVTEX file - 2 figure
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