5,168 research outputs found
Os mais primitivos nomes da PenĂnsula Hispânica.
56 (3-4) Jul.-Dez. 1946, p. 227-250
OrĂgines de la casa redonda de la cultura castreña del N. O. de la Peninsula.
81 (1-2) Jan.-Jun. 1971, p. 25-35
El Castro de Coaña (Asturias) y algunas notas sobre el posible origen de esta cultura.
50 (3-4) Jul.-Dez. 1940, p. 284-311
Uncertainties of predictions in models of eternal inflation
In a previous paper \cite{MakingPredictions}, a method of comparing the
volumes of thermalized regions in eternally inflating universe was introduced.
In this paper, we investigate the dependence of the results obtained through
that method on the choice of the time variable and factor ordering in the
diffusion equation that describes the evolution of eternally inflating
universes. It is shown, both analytically and numerically, that the variation
of the results due to factor ordering ambiguity inherent in the model is of the
same order as their variation due to the choice of the time variable.
Therefore, the results are, within their accuracy, free of the spurious
dependence on the time parametrization.Comment: 30 pages, RevTeX, figure included, added some references and Comments
on recent proposal (gr-qc/9511058) of alternative regularization schemes, to
appear in Phys. Rev.
Corrections to the apparent value of the cosmological constant due to local inhomogeneities
Supernovae observations strongly support the presence of a cosmological
constant, but its value, which we will call apparent, is normally determined
assuming that the Universe can be accurately described by a homogeneous model.
Even in the presence of a cosmological constant we cannot exclude nevertheless
the presence of a small local inhomogeneity which could affect the apparent
value of the cosmological constant. Neglecting the presence of the
inhomogeneity can in fact introduce a systematic misinterpretation of
cosmological data, leading to the distinction between an apparent and true
value of the cosmological constant. We establish the theoretical framework to
calculate the corrections to the apparent value of the cosmological constant by
modeling the local inhomogeneity with a solution. Our assumption
to be at the center of a spherically symmetric inhomogeneous matter
distribution correspond to effectively calculate the monopole contribution of
the large scale inhomogeneities surrounding us, which we expect to be the
dominant one, because of other observations supporting a high level of isotropy
of the Universe around us.
By performing a local Taylor expansion we analyze the number of independent
degrees of freedom which determine the local shape of the inhomogeneity, and
consider the issue of central smoothness, showing how the same correction can
correspond to different inhomogeneity profiles. Contrary to previous attempts
to fit data using large void models our approach is quite general. The
correction to the apparent value of the cosmological constant is in fact
present for local inhomogeneities of any size, and should always be taken
appropriately into account both theoretically and observationally.Comment: 16 pages,new sections added analyzing central smoothness and accuracy
of the Taylor expansion approach, Accepted for publication by JCAP. An essay
based on this paper received honorable mention in the 2011 Essay Context of
the Gravity Research Foundatio
Chaotic behavior in a Z_2 x Z_2 field theory
We investigate the presence of chaos in a system of two real scalar fields
with discrete Z_2 x Z_2 symmetry. The potential that identify the system is
defined with a real parameter r and presents distinct features for r>0 and for
r<0. For static field configurations, the system supports two topological
sectors for r>0, and only one for r<0. Under the assumption of spatially
homogeneous fields, the system exhibts chaotic behavior almost everywhere in
parameter space. In particular a more complex dynamics appears for r>0; in this
case chaos can decrease for increasing energy, a fact that is absent for r<0.Comment: Revtex, 13 pages, no figures. Version with figures in Int. J. Mod.
Phys. A14 (1999) 496
Predictability crisis in inflationary cosmology and its resolution
Models of inflationary cosmology can lead to variation of observable
parameters ("constants of Nature") on extremely large scales. The question of
making probabilistic predictions for today's observables in such models has
been investigated in the literature. Because of the infinite thermalized volume
resulting from eternal inflation, it has proven difficult to obtain a
meaningful and unambiguous probability distribution for observables, in
particular due to the gauge dependence. In the present paper, we further
develop the gauge-invariant procedure proposed in a previous work for models
with a continuous variation of "constants". The recipe uses an unbiased
selection of a connected piece of the thermalized volume as sample for the
probability distribution. To implement the procedure numerically, we develop
two methods applicable to a reasonably wide class of models: one based on the
Fokker-Planck equation of stochastic inflation, and the other based on direct
simulation of inflationary spacetime. We present and compare results obtained
using these methods.Comment: 23 pages, 13 figure
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