4,168 research outputs found
On the conformally coupled scalar field quantum cosmology
We propose a new initial condition for the homogeneous and isotropic quantum
cosmology, where the source of the gravitational field is a conformally coupled
scalar field, and the maximally symmetric hypersurfaces have positive
curvature. After solving corresponding Wheeler-DeWitt equation, we obtain exact
solutions in both classical and quantum levels. We propose appropriate initial
condition for the wave packets which results in a complete classical and
quantum correspondence. These wave packets closely follow the classical
trajectories and peak on them. We also quantify this correspondence using
de-Broglie Bohm interpretation of quantum mechanics. Using this proposal, the
quantum potential vanishes along the Bohmian paths and the classical and
Bohmian trajectories coincide with each other. We show that the model contains
singularities even at the quantum level. Therefore, the resulting wave packets
closely follow the classical trajectories from big-bang to big-crunch.Comment: 14 pages, 4 figures, to appear in PL
Path integral for minisuperspaces and its relation with non equivalent canonical quantizations
The relation between a recently proposed path integral for minisuperspaces
and different canonical quantizations is established. The step of the procedure
where a choice between non equivalent theories is made is identified.
Coordinates avoiding such a choice are found for a class of homogeneous
cosmologies.Comment: 11 pages, to appear in Physics Letters
Gauge invariance of parametrized systems and path integral quantization
Gauge invariance of systems whose Hamilton-Jacobi equation is separable is
improved by adding surface terms to the action fuctional. The general form of
these terms is given for some complete solutions of the Hamilton-Jacobi
equation. The procedure is applied to the relativistic particle and toy
universes, which are quantized by imposing canonical gauge conditions in the
path integral; in the case of empty models, we first quantize the parametrized
system called ``ideal clock'', and then we examine the possibility of obtaining
the amplitude for the minisuperspaces by matching them with the ideal clock.
The relation existing between the geometrical properties of the constraint
surface and the variables identifying the quantum states in the path integral
is discussed.Comment: 23 page
Global phase time and path integral for the Kantowski--Sachs anisotropic univers
The action functional of the anisotropic Kantowski--Sachs cosmological model
is turned into that of an ordinary gauge system. Then a global phase time is
identified for the model by imposing canonical gauge conditions, and the
quantum transition amplitude is obtained by means of the usual path integral
procedure of Fadeev and Popov.Comment: 11 page
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
Growth performance and antioxidant status of growing rabbits fed on diets supplemented with Eucommia ulmoides leaves
[EN] The present study evaluated the effect of dietary Eucommia ulmoides leaves (EUL) on growth performance and antioxidant status of growing rabbits under heat stress condition. Four hundred and fifty weaned New Zealand male rabbits (6 wk old) were randomly divided into 3 equal groups (150 rabbits/group) and fed with a basal diet (control, digestible energy (DE): 15.92 MJ/kg and crude protein (CP): 19.24%) or the basal diet supplemented with 1 or 5 g of EUL/kg of diet (EUL1 and EUL5), in which the same quantity of barley meal was replaced. During the 21 d of experiment (43 to 63 d of age), the temperature and relative humidity of the rabbit house ranged from 27.5 to 32.5°C and from 65 to 73%, respectively. We analysed feed intake, growth performance and antioxidant status of growing rabbits. Compared with the control group, at the end of the experimental period, EUL supplementation significantly reduced the average daily feed intake (92.0, 92.8 and 100.7 g/d for EUL1, EUL5 and control, respectively; P<0.05), improved the feed conversion ratio (3.80, 3.81 and 4.59 for EUL1, EUL5 and control, respectively; P<0.05), increased the activities of glutathione peroxidase (+35.5 and +35.0% in plasma and liver of rabbits in EUL5 vs. control group, respectively; P<0.05) and reduced those of malondialdehyde (–12.0 and –46.0% in plasma and liver of rabbits in EUL5 vs. control group, respectively; P<0.05). These results suggest that inclusion of EUL in the diet of growing rabbits improved the growth performance and antioxidant status in growing rabbits.This study was supported by the Science and Technology Development Plan of Tai’an, China (2016NS1051), College Students’ Innovation and Entrepreneurship Training Programme of China (201610439269 and 201710439327), National Natural Science Foundation of China (81672093), and Key Research and Development Programme of Shandong Province, China (2016GSF201155).Li, S.; Zhao, M.; Jiang, T.; Lv, W.; Gao, S.; Zhou, Y.; Miao, Z. (2018). Growth performance and antioxidant status of growing rabbits fed on diets supplemented with Eucommia ulmoides leaves. World Rabbit Science. 26(1):35-41. https://doi.org/10.4995/wrs.2018.7864SWORD354126
On the Relationship Between Complex Potentials and Strings of Projection Operators
It is of interest in a variety of contexts, and in particular in the arrival
time problem, to consider the quantum state obtained through unitary evolution
of an initial state regularly interspersed with periodic projections onto the
positive -axis (pulsed measurements). Echanobe, del Campo and Muga have
given a compelling but heuristic argument that the state thus obtained is
approximately equivalent to the state obtained by evolving in the presence of a
certain complex potential of step-function form. In this paper, with the help
of the path decomposition expansion of the associated propagators, we give a
detailed derivation of this approximate equivalence. The propagator for the
complex potential is known so the bulk of the derivation consists of an
approximate evaluation of the propagator for the free particle interspersed
with periodic position projections. This approximate equivalence may be used to
show that to produce significant reflection, the projections must act at time
spacing less than 1/E, where E is the energy scale of the initial state.Comment: 29 pages, LaTex, 4 figures. Substantial revision
Actes du Congrès Collèges célébrations 92
Également disponible en version papierTitre de l'écran-titre (visionné le 19 août 2009
Classical analogous of quantum cosmological perfect fluid models
Quantization in the mini-superspace of a gravity system coupled to a perfect
fluid, leads to a solvable model which implies singularity free solutions
through the construction of a superposition of the wavefunctions. We show that
such models are equivalent to a classical system where, besides the perfect
fluid, a repulsive fluid with an equation of state is present.
This leads to speculate on the true nature of this quantization procedure. A
perturbative analysis of the classical system reveals the condition for the
stability of the classical system in terms of the existence of an anti-gravity
phase.Comment: Latex file, 10 pages, 3 figure
An Anisotropic Wormhole:TUNNELLING in Time and Space
We discuss the structure of a gravitational euclidean instanton obtained
through coupling of gravity to electromagnetism. Its topology at fixed is
. This euclidean solution can be interpreted as a tunnelling to
a hyperbolic space (baby universe) at or alternatively as a static
wormhole that joins the two asymptotically flat spaces of a
Reissner--Nordstr\"om type solution with .Comment: PLAIN-TEX, 16 pages (4 figures not included), Report DFTT 2/9
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