103 research outputs found
The arrow of time: from universe time-asymmetry to local irreversible processes
In several previous papers we have argued for a global and non-entropic
approach to the problem of the arrow of time, according to which the ''arrow''
is only a metaphorical way of expressing the geometrical time-asymmetry of the
universe. We have also shown that, under definite conditions, this global
time-asymmetry can be transferred to local contexts as an energy flow that
points to the same temporal direction all over the spacetime. The aim of this
paper is to complete the global and non-entropic program by showing that our
approach is able to account for irreversible local phenomena, which have been
traditionally considered as the physical origin of the arrow of time.Comment: 48 pages, 8 figures, revtex4. Accepted for publication in Foundations
of Physic
Functional Approach to Quantum Decoherence and the Classical Final Limit
For a wide set of quantum systems it is demonstrated that the quantum regime
can be considered as the transient phase while the final classical statistical
regime is a permanent state. A basis where exact matrix decoherence appears for
these final states is found. The relation with the decoherence of histories
formalism is studied. A set of final intrinsically consistent histories is
found.Comment: 20 pages. Phys. Rev A in press 200
Thermal Conditions for Scalar Bosons in a Curved Space Time
The conditions that allow us to consider the vacuum expectation value of the
energy-momentum tensor as a statistical average, at some particular
temperature, are given. When the mean value of created particles is stationary,
a planckian distribution for the field modes is obtained. In the massless
approximation, the temperature dependence is as that corresponding to a
radiation dominated Friedmann-like model.Comment: 14 pages (TeX manuscript
Decoherence time in self-induced decoherence
A general method for obtaining the decoherence time in self-induced
decoherence is presented. In particular, it is shown that such a time can be
computed from the poles of the resolvent or of the initial conditions in the
complex extension of the Hamiltonian's spectrum. Several decoherence times are
estimated: for microscopic systems, and
for macroscopic bodies. For the particular case of a
thermal bath, our results agree with those obtained by the einselection
(environment-induced decoherence) approach.Comment: 11 page
A Unified Conformal Model for Fundamental Interactions without Dynamical Higgs Field
A Higgsless model for strong, electro-weak and gravitational interactions is
proposed. This model is based on the local symmetry group SU(3)xSU(2)xU(1)xC
where C is the local conformal symmetry group. The natural minimal conformally
invariant form of total lagrangian is postulated. It contains all Standard
Model fields and gravitational interaction. Using the unitary gauge and the
conformal scale fixing conditions we can eliminate all four real components of
the Higgs doublet in this model. However the masses of vector mesons, leptons
and quarks are automatically generated and are given by the same formulas as in
the conventional Standard Model. The gravitational sector is analyzed and it is
shown that the model admits in the classical limit the Einsteinian form of
gravitational interactions. No figures.Comment: 25 pages, preprin
A time-dependent perturbative analysis for a quantum particle in a cloud chamber
We consider a simple model of a cloud chamber consisting of a test particle
(the alpha-particle) interacting with two other particles (the atoms of the
vapour) subject to attractive potentials centered in . At time zero the alpha-particle is described by an outgoing
spherical wave centered in the origin and the atoms are in their ground state.
We show that, under suitable assumptions on the physical parameters of the
system and up to second order in perturbation theory, the probability that both
atoms are ionized is negligible unless lies on the line joining the
origin with . The work is a fully time-dependent version of the original
analysis proposed by Mott in 1929.Comment: 23 page
Statistical Mechanics for Unstable States in Gel'fand Triplets and Investigations of Parabolic Potential Barriers
Free energies and other thermodynamical quantities are investigated in
canonical and grand canonical ensembles of statistical mechanics involving
unstable states which are described by the generalized eigenstates with complex
energy eigenvalues in the conjugate space of Gel'fand triplet. The theory is
applied to the systems containing parabolic potential barriers (PPB's). The
entropy and energy productions from PPB systems are studied. An equilibrium for
a chemical process described by reactions is also
discussed.Comment: 14 pages, AmS-LaTeX, no figur
Predição do consumo de matéria seca de cabras leiteiras durante a gestação.
Resumo: O período da gestação é caracterizado por importantes mudanças fisiológicas no corpo materno tais como a diminuição da ingestão de alimento no último terço de gestação em fêmeas com gestação de múltiplos fetos. O objetivo desse estudo foi desenvolver modelos para predizer a ingestão de matéria seca (IMS) em cabras durante gestação simples e gemelar. Parar este estudo, foram usadas 1820 observações de IMS, obtidos diariamente a partir de sete cabras com gestação gemelar e seis cabras com gestação simples a partir do primeiro dia até os 140 dias de gestação. A IMS diária foi ajustada em três modelos não lineares, os quais foram avaliados através do critério de informação Bayesiana (BIC) como um indicador de melhor ajuste do modelo aos dados. O modelo que melhor se ajustou aos dados foi o modelo quadrático, com valor de BIC de 11549. Os interceptos e coeficientes de regressões do modelo quadrático utilizado para predição do IMS diário foram diferentes entre gestação simples e gemelar (P< 0.01). Comparado as cabras com gestação simples, as cabras com gestação gemelar tiveram maior decréscimo na IMS durante a gestação. Esse decréscimo na IMS em fêmeas com gestação gemelar se deve principalmente a mudanças hormonais e a maior compressão ruminal causada pelo maior tamanho de seus úteros grávidos. Os modelos desenvolvidos nesse estudo devem de ser considerados no manejo nutricional de cabras leiteiras durante a gestação. [Prediction of dry matter intake of dairy goats during pregnancy]. Abstract: The pregnancy is characterized by important physiological changes in maternal body such as a decrease on feed intake in the last third of pregnancy mainly in pregnancy of multiples fetuses. The objective of this study was to develop a model to predict the dry matter intake (DMI) of dairy goats carrying single and twin fetuses throughout pregnancy. For this study it was used a total of 1820 individual records of DMI from seven goats carrying twins and six goats carrying single fetuses. The DMI was daily recorded from the first up to 140 days of pregnancy. The daily DMI as a proportion of the average BW was fitted to tree non-linear models which were evaluated considering the Bayesian information criterion (BIC) value as an indicator how well the model fit the data. The best model fitting the data was the quadratic model with had BIC value of 11549. The intercepts and the slopes of the quadratic models used to predict the daily DMI were different between litter sizes (P < 0.01). Goats carrying twin fetuses showed a greater decrease in the DMI during pregnancy compared to goats carrying single fetus. The decrease of feed intake in females carrying twins may be mainly related to hormonal changes and a greatest rumen compression due to the biggest size of the gravid uterus. The models developed in this study may be relevant in the adoption of nutritional management of dairy goats during the pregnancy
Third quantization of -type gravity
We examine the third quantization of -type gravity, based on its
effective Lagrangian in the case of a flat Friedmann-Lemaitre-Robertson-Walker
metric. Starting from the effective Lagrangian, we execute a suitable change of
variable and the second quantization, and we obtain the Wheeler-DeWitt
equation. The third quantization of this theory is considered. And the
uncertainty relation of the universe is investigated in the example of
-type gravity, where . It is shown, when the time is late
namely the scale factor of the universe is large, the spacetime does not
contradict to become classical, and, when the time is early namely the scale
factor of the universe is small, the quantum effects are dominating.Comment: 9 pages, Arbitrary constants in (4.19) are changed to arbitrary
functions of . Conclusions are not changed. References are added.
Typos are correcte
The Isaacson expansion in quantum cosmology
This paper is an application of the ideas of the Born-Oppenheimer (or
slow/fast) approximation in molecular physics and of the Isaacson (or
short-wave) approximation in classical gravity to the canonical quantization of
a perturbed minisuperspace model of the kind examined by Halliwell and Hawking.
Its aim is the clarification of the role of the semiclassical approximation and
the backreaction in such a model. Approximate solutions of the quantum model
are constructed which are not semiclassical, and semiclassical solutions in
which the quantum perturbations are highly excited.Comment: Revtex, 11 journal or 24 preprint pages. REPLACEMENT: A comment on
previous work by Dowker and Laflamme is corrected. Utah preprint
UU-REL-93/3/1
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