34 research outputs found
Vacuum effective action and inflation
We consider vacuum quantum effects in the Early Universe, which may lead to
inflation. The inflation is a direct consequence of the supposition that, at
high energies, all the particles can be described by the weakly interacting,
massless, conformally invariant fields. We discuss, from the effective field
theory point of view, the stability of inflation, transition to the FRW
solution, and also possibility to study metric and density perturbations.Comment: 6 pages, LaTeX, no figures. Contribution to the Proceedings of the X
Jorge Andre Swieca school in Particles and Fields. To be published in World
Scientifi
The anomaly-induced effective action and natural inflation
The anomaly-induced inflation (modified Starobinsky model) is based on the
application of the effective quantum field theory approach to the Early
Universe. We present a brief general review of the model and show that it does
not require a fine-tuning for the parameters of the theory or initial data,
gives a real chance to meet a graceful exit to the FRW phase and also has
positive features with respect to the metric perturbations.Comment: Invited talk at the International Workshop on Astroparticle and High
Energy Physics, October 14 - 18, 2003, Valencia, Spai
Effective growth of matter density fluctuations in the running LCDM and LXCDM models
We investigate the matter density fluctuations \delta\rho/\rho for two dark
energy (DE) models in the literature in which the cosmological term \Lambda is
a running parameter. In the first model, the running LCDM model, matter and DE
exchange energy, whereas in the second model, the LXCDM model, the total DE and
matter components are conserved separately. The LXCDM model was proposed as an
interesting solution to the cosmic coincidence problem. It includes an extra
dynamical component, the "cosmon" X, which interacts with the running \Lambda,
but not with matter. In our analysis we make use of the current value of the
linear bias parameter, b^2(0)= P_{GG}/P_{MM}, where P_{MM} ~
(\delta\rho/\rho)^2 is the present matter power spectrum and P_{GG} is the
galaxy fluctuation power spectrum. The former can be computed within a given
model, and the latter is found from the observed LSS data (at small z) obtained
by the 2dF galaxy redshift survey. It is found that b^2(0)=1 within a 10%
accuracy for the standard LCDM model. Adopting this limit for any DE model and
using a method based on the effective equation of state for the DE, we can set
a limit on the growth of matter density perturbations for the running LCDM
model, the solution of which is known. This provides a good test of the
procedure, which we then apply to the LXCDM model in order to determine the
physical region of parameter space, compatible with the LSS data. In this
region, the LXCDM model is consistent with known observations and provides at
the same time a viable solution to the cosmic coincidence problem.Comment: LaTeX, 38 pages, 8 figures. Version accepted in JCA
Dark energy perturbations and cosmic coincidence
While there is plentiful evidence in all fronts of experimental cosmology for
the existence of a non-vanishing dark energy (DE) density \rho_D in the
Universe, we are still far away from having a fundamental understanding of its
ultimate nature and of its current value, not even of the puzzling fact that
\rho_D is so close to the matter energy density \rho_M at the present time
(i.e. the so-called "cosmic coincidence" problem). The resolution of some of
these cosmic conundrums suggests that the DE must have some (mild) dynamical
behavior at the present time. In this paper, we examine some general properties
of the simultaneous set of matter and DE perturbations (\delta\rho_M,
\delta\rho_D) for a multicomponent DE fluid. Next we put these properties to
the test within the context of a non-trivial model of dynamical DE (the LXCDM
model) which has been previously studied in the literature. By requiring that
the coupled system of perturbation equations for \delta\rho_M and \delta\rho_D
has a smooth solution throughout the entire cosmological evolution, that the
matter power spectrum is consistent with the data on structure formation and
that the "coincidence ratio" r=\rho_D/\rho_M stays bounded and not unnaturally
high, we are able to determine a well-defined region of the parameter space
where the model can solve the cosmic coincidence problem in full compatibility
with all known cosmological data.Comment: Typos correcte
Evolução da maturação e características físicoquímicas da videira "BRS Vitória" em diferentes épocas de poda.
Na região noroeste paulista são realizadas duas podas no mesmo ano, a primeira de produção, realizada de fevereiro a junho, e a segunda para formação, realizada entre junho a novembro. O período de colheita se estende de julho a novembro, diferentemente de outras regiões produtoras, o que beneficia os produtores na comercialização da uva
The scaling evolution of cosmological constant
In quantum field theory the parameters of the vacuum action are subject to
renormalization group running. In particular, the ``cosmological constant'' is
not a constant in a quantum field theory context, still less should be zero. In
this paper we continue with previous work, and derive the particle
contributions to the running of the cosmological and gravitational constants in
the framework of the Standard Model in curved space-time. At higher energies
the calculation is performed in a sharp cut off approximation. We assess, in
two different frameworks, whether the scaling dependences of the cosmological
and gravitational constants spoil primordial nucleosynthesis. Finally, the
cosmological implications of the running of the cosmological constant are
discussed.Comment: 25 pages, 1 figure using axodraw. Extended version. The title and the
part of the discussion concerning a gravitational energy scale modified. The
new section about the role of the cosmological constant in the
anomaly-induced inflation added. Misprint in one reference correcte
Cosmic perturbations with running G and Lambda
Cosmologies with running cosmological term (Lambda) and gravitational
Newton's coupling (G) may naturally be expected if the evolution of the
universe can ultimately be derived from the first principles of Quantum Field
Theory or String Theory. In this paper, we derive the general cosmological
perturbation equations for models with variable G and Lambda in which the
fluctuations in both variables are explicitly included. We demonstrate that, if
matter is covariantly conserved, the late growth of matter density
perturbations is independent of the wavenumber. Furthermore, if Lambda is
negligible at high redshifts and G varies slowly, we find that these
cosmologies produce a matter power spectrum with the same shape as that of the
concordance LCDM model, thus predicting the same basic features on structure
formation. Despite this shape indistinguishability, the free parameters of the
variable G and Lambda models can still be effectively constrained from the
observational bounds on the spectrum amplitude.Comment: Accepted in Classical and Quantum Gravity. One appendix on
perturbations in the Newtonian gauge added. Extended discussion and new
references