4,607 research outputs found
Cosmic acceleration: Inhomogeneity versus vacuum energy
In this essay, I present an alternative explanation for the cosmic
acceleration which appears as a consequence of recent high redshift Supernova
data. In the usual interpretation, this cosmic acceleration is explained by the
presence of a positive cosmological constant or vacuum energy, in the
background of Friedmann models. Instead, I will consider a Local Rotational
Symmetric (LRS) inhomogeneous spacetime, with a barotropic equation of state
for the cosmic matter. Within this framework the kinematical acceleration of
the cosmic fluid or, equivalently, the inhomogeneity of matter, is just the
responsible of the SNe Ia measured cosmic acceleration. Although in our model
the Cosmological Principle is relaxed, it maintains local isotropy about our
worldline in agreement with the CBR experiments.Comment: LATEX, 7 pags, no figs, Honorable Mention in the 1999 Essay
Competition of the Gravity Research Foundatio
Non-stationary de Sitter cosmological models
In this note it is proposed a class of non-stationary de Sitter, rotating and
non-rotating, solutions of Einstein's field equations with a cosmological term
of variable function.Comment: 11 pages, Latex. International Journal of Modern Physics D (accepted
for publication
On the variable-charged black holes embedded into de Sitter space: Hawking's radiation
In this paper we study the Hawking evaporation of masses of variable-charged
Reissner-Nordstrom and Kerr-Newman, black holes embedded into the de Sitter
universe by considering the charge to be function of radial coordinate of the
spherically symmetric metric.Comment: LaTex, p. 2
The Functional Derivation of Master Equations
Master equations describe the quantum dynamics of open systems interacting
with an environment. They play an increasingly important role in understanding
the emergence of semiclassical behavior and the generation of entropy, both
being related to quantum decoherence. Presently we derive the exact master
equation for a homogeneous scalar Higgs or inflaton like field coupled to an
environment field represented by an infinite set of harmonic oscillators. Our
aim is to demonstrate a derivation directly from the path integral
representation of the density matrix propagator. Applications and
generalizations of this result are discussed.Comment: 10 pages; LaTex. - Contribution to the workshop Hadron Physics VI,
March 1998, Florianopolis (Brazil); proceedings, E. Ferreira et al., eds.
(World Scientific). Replaced by slightly modified published versio
Colliding Bubble Worlds
We consider a cosmological model in which our Universe is a spherically
symmetric bubble wall in 5-dimensional anti-de Sitter spacetime. We argue that
the bubble on which we live will undergo collisions with other similar bubbles
and estimate the spectrum of such collisions. The collision rate is found to be
independent of the age of our Universe. Collisions with small bubbles provide
an experimental signature of this scenario, while collisions with larger
bubbles would be catastrophic.Comment: 7 pages, no figure
Post-Newtonian expansion for Gauss-Bonnet Gravity
The Parametrized Post-Newtonian expansion of gravitational theories with a
scalar field coupled to the Gauss-Bonnet invariant is performed and
confrontation of such theories with Solar system experiments is discussed.Comment: 4 pages; typos corrected, published versio
Bubble collisions and measures of the multiverse
To compute the spectrum of bubble collisions seen by an observer in an
eternally-inflating multiverse, one must choose a measure over the diverging
spacetime volume, including choosing an "initial" hypersurface below which
there are no bubble nucleations. Previous calculations focused on the case
where the initial hypersurface is pushed arbitrarily deep into the past.
Interestingly, the observed spectrum depends on the orientation of the initial
hypersurface, however one's ability observe the effect rapidly decreases with
the ratio of inflationary Hubble rates inside and outside one's bubble. We
investigate whether this conclusion might be avoided under more general
circumstances, in particular placing the observer's bubble near the initial
hypersurface. We find that it is not. As a point of reference, a substantial
appendix reviews relevant aspects of the measure problem of eternal inflation.Comment: 24 pages, two figures, plus 16-page appendix with one figure; v2:
minor improvements and clarifications, conclusions unchanged (version to
appear in JCAP
Spatial Curvature Falsifies Eternal Inflation
Inflation creates large-scale cosmological density perturbations that are
characterized by an isotropic, homogeneous, and Gaussian random distribution
about a locally flat background. Even in a flat universe, the spatial curvature
measured within one Hubble volume receives contributions from long wavelength
perturbations, and will not in general be zero. These same perturbations
determine the Cosmic Microwave Background (CMB) temperature fluctuations, which
are O(10^-5). Consequently, the low-l multipole moments in the CMB temperature
map predict the value of the measured spatial curvature \Omega_k. On this basis
we argue that a measurement of |\Omega_k| > 10^-4 would rule out slow-roll
eternal inflation in our past with high confidence, while a measurement of
\Omega_k < -10^-4 (which is positive curvature, a locally closed universe)
rules out false-vacuum eternal inflation as well, at the same confidence level.
In other words, negative curvature (a locally open universe) is consistent with
false-vacuum eternal inflation but not with slow-roll eternal inflation, and
positive curvature falsifies both. Near-future experiments will dramatically
extend the sensitivity of \Omega_k measurements and constitute a sharp test of
these predictions.Comment: 16+2 pages, 2 figure
Effect of strong magnetic field on the first-order electroweak phase transition
The broken-symmetry electroweak vacuum is destabilized in the presence of a
magnetic field stronger than a critical value. Such magnetic field may be
generated in the phase transition and restore the symmetry inside the bubbles.
A numerical calculation indicates that the first-order phase transition is
delayed but may be completed for a sufficient low value of the Higgs mass
unless the magnetic field is extremely high.Comment: 7 pages including 2 figures, uses epsf.sty; discussion regarding
cosmological consequences (e.g. on baryogenesis) enlarged, some references
added and a few misprints correcte
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