4,705 research outputs found
Covariant many-fingered time Bohmian interpretation of quantum field theory
The Bohmian interpretation of the many-fingered time (MFT) Tomonaga-Schwinger
formulation of quantum field theory (QFT) describes MFT fields, which provides
a covariant Bohmian interpretation of QFT without introducing a preferred
foliation of spacetime.Comment: 7 pages, significantly revise
Bohmian quantum gravity and cosmology
Quantum gravity aims to describe gravity in quantum mechanical terms. How
exactly this needs to be done remains an open question. Various proposals have
been put on the table, such as canonical quantum gravity, loop quantum gravity,
string theory, etc. These proposals often encounter technical and conceptual
problems. In this chapter, we focus on canonical quantum gravity and discuss
how many conceptual problems, such as the measurement problem and the problem
of time, can be overcome by adopting a Bohmian point of view. In a Bohmian
theory (also called pilot-wave theory or de Broglie-Bohm theory, after its
originators de Broglie and Bohm), a system is described by certain variables in
space-time such as particles or fields or something else, whose dynamics
depends on the wave function. In the context of quantum gravity, these
variables are a space-time metric and suitable variable for the matter fields
(e.g., particles or fields). In addition to solving the conceptual problems,
the Bohmian approach yields new applications and predictions in quantum
cosmology. These include space-time singularity resolution, new types of
semi-classical approximations to quantum gravity, and approximations for
quantum perturbations moving in a quantum background.Comment: 45 pages, 6 figures, PDFLaTeX; written for "Applied Bohmian
Mechanics: From Nanoscale Systems to Cosmology", edited by Xavier Oriols
Pladevall and Jordi Mompart; v2 typos correcte
The accelerated expansion of the Universe as a quantum cosmological effect
We study the quantized Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) model
minimally coupled to a free massless scalar field. In a previous paper,
\cite{fab2}, solutions of this model were constructed as gaussian
superpositions of negative and positive modes solutions of the Wheeler-DeWitt
equation, and quantum bohmian trajectories were obtained in the framework of
the Bohm-de Broglie (BdB) interpretation of quantum cosmology. In the present
work, we analyze the quantum bohmian trajectories of a different class of
gaussian packets. We are able to show that this new class generates bohmian
trajectories which begin classical (with decelerated expansion), undergo an
accelerated expansion in the middle of its evolution due to the presence of
quantum cosmological effects in this period, and return to its classical
decelerated expansion in the far future. We also show that the relation between
luminosity distance and redshift in the quantum cosmological model can be made
close to the corresponding relation coming from the classical model suplemented
by a cosmological constant, for . These results suggest the posibility of
interpreting the present observations of high redshift supernovae as the
manifestation of a quantum cosmological effect
Spectra of primordial fluctuations in two-perfect-fluid regular bounces
We introduce analytic solutions for a class of two components bouncing
models, where the bounce is triggered by a negative energy density perfect
fluid. The equation of state of the two components are constant in time, but
otherwise unrelated. By numerically integrating regular equations for scalar
cosmological perturbations, we find that the (would be) growing mode of the
Newtonian potential before the bounce never matches with the the growing mode
in the expanding stage. For the particular case of a negative energy density
component with a stiff equation of state we give a detailed analytic study,
which is in complete agreement with the numerical results. We also perform
analytic and numerical calculations for long wavelength tensor perturbations,
obtaining that, in most cases of interest, the tensor spectral index is
independent of the negative energy fluid and given by the spectral index of the
growing mode in the contracting stage. We compare our results with previous
investigations in the literature.Comment: 11 pages, 5 figure
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