368 research outputs found
Theory for the Secondary Eclipse Fluxes, Spectra, Atmospheres, and Light Curves of Transiting Extrasolar Giant Planets
We have created a general methodology for calculating the
wavelength-dependent light curves of close-in extrasolar giant planets (EGPs)
as they traverse their orbits. Focussing on the transiting EGPs HD189733b,
TrES-1, and HD209458b, we calculate planet/star flux ratios during secondary
eclipse and compare them with the Spitzer data points obtained so far in the
mid-infrared. We introduce a simple parametrization for the redistribution of
heat to the planet's nightside, derive constraints on this parameter (P_n), and
provide a general set of predictions for planet/star contrast ratios as a
function of wavelength, model, and phase. Moreover, we calculate average
dayside and nightside atmospheric temperature/pressure profiles for each
transiting planet/P_n pair with which existing and anticipated Spitzer data can
be used to probe the atmospheric thermal structure of severely irradiated EGPs.
We find that the baseline models do a good job of fitting the current secondary
eclipse dataset, but that the Spitzer error bars are not yet small enough to
discriminate cleanly between all the various possibilities.Comment: 14 figures, 7 text pages (in two-column emulateapj format); Accepted
to the Ap.J. June 26, 2006; one cosmetic change made to astro-ph version
A signature of quantum gravity at the source of the seeds of cosmic structure?
This article reviews a recent work by a couple of colleagues and myself about
the shortcomings of the standard explanations of the quantum origin of cosmic
structure in the inflationary scenario, and a proposal to address them. The
point it that in the usual accounts the inhomogeneity and anisotropy of our
universe seem to emerge from an exactly homogeneous and isotropic initial state
through processes that do not break those symmetries. We argued that some novel
aspect of physics must be called upon to able to address the problem in a fully
satisfactory way. The proposed approach is inspired on Penrose's ideas
regarding an quantum gravity induced, real and dynamical collapse of the wave
function.Comment: LateX, (jpconference macros), Prepared for the proceedings the Third
International Workshop DICE 2006, " Quantum Mechanics between decoherence and
Determinism
When is S=A/4?
Black hole entropy and its relation to the horizon area are considered. More
precisely, the conditions and specifications that are expected to be required
for the assignment of entropy, and the consequences that these expectations
have when applied to a black hole are explored. In particular, the following
questions are addressed: When do we expect to assign an entropy?; when are
entropy and area proportional? and, what is the nature of the horizon? It is
concluded that our present understanding of black hole entropy is somewhat
incomplete, and some of the relevant issues that should be addressed in
pursuing these questions are pointed out.Comment: 14 pages, no figures. Revtex file. Manuscript edited and discussion
expanded. References added, conclusions unchanged. Version to be published in
MPL
Phenomenological analysis of quantum collapse as source of the seeds of cosmic structure
The standard inflationary version of the origin of the cosmic structure as
the result of the quantum fluctuations during the early universe is less than
fully satisfactory as has been argued in [A. Perez, H. Sahlmann, and D.
Sudarsky, Class. Quantum Grav., 23, 2317, (2006)]. A proposal is made there of
a way to address the shortcomings by invoking a process similar to the collapse
of the quantum mechanical wave function of the various modes of the inflaton
field. This in turn was inspired on the ideas of R. Penrose about the role that
quantum gravity might play in bringing about such breakdown of the standard
unitary evolution of quantum mechanics. In this paper we study in some detail
the two schemes of collapse considered in the original work together with an
alternative scheme, which can be considered as "more natural" than the former
two. The new scheme, assumes that the collapse follows the correlations
indicated in the Wigner functional of the initial state. We end with
considerations regarding the degree to which the various schemes can be
expected to produce a spectrum that resembles the observed one.Comment: 18 pages, 9 figure
Equivalence Principle in Chameleon Models
Most theories that predict time and/or space variation of fundamental
constants also predict violations of the Weak Equivalence Principle. In 2004
Khoury and Weltman proposed the so called chameleon field arguing that it could
help avoiding experimental bounds on the WEP while having a non-trivial
cosmological impact. In this paper we revisit the extent to which these
expectations continue to hold as we enter the regime of high precision tests.
The basis of the study is the development of a new method for computing the
force between two massive bodies induced by the chameleon field which takes
into account the influence on the field by both, the large and the test bodies.
We confirm that in the thin shell regime the force does depend non-trivially on
the test body\' s composition, even when the chameleon coupling constants are
universal. We also propose a simple criterion based on energy minimization,
that we use to determine which of the approximations used in computing the
scalar field in a two body problem is better in each specific regime. As an
application of our analysis we then compare the resulting differential
acceleration of two test bodies with the corresponding bounds obtained from
E\"otv\"os type experiments. We consider two setups: 1) an Earth based
experiment where the test bodies are made of Be and Al; 2) the Lunar Laser
Ranging experiment. We find that for some choices of the free parameters of the
chameleon model the predictions of the E\"otv\"os parameter are larger than
some of the previous estimates. As a consequence, we put new constrains on
these free parameters. An important result of our analysis is that our approach
leads to new constraints on the parameter space of the chameleon models.Comment: 42 pages, 15 figures Accepted for publication in PR
Galactic periodicity and the oscillating G model
We consider the model involving the oscillation of the effective
gravitational constant that has been put forward in an attempt to reconcile the
observed periodicity in the galaxy number distribution with the standard
cosmological models. This model involves a highly nonlinear dynamics which we
analyze numerically. We carry out a detailed study of the bound that
nucleosynthesis imposes on this model. The analysis shows that for any assumed
value for (the total energy density) one can fix the value of
(the baryonic energy density) in such a way as to
accommodate the observational constraints coming from the
primordial abundance. In particular, if we impose the inflationary value
the resulting baryonic energy density turns out to be . This result lies in the very narrow range allowed by the observed values of the primordial
abundances of the other light elements. The remaining fraction of
corresponds to dark matter represented by a scalar field.Comment: Latex file 29 pages with no figures. Please contact M.Salgado for
figures. A more careful study of the model appears in gr-qc/960603
Spectra and Diagnostics for the Direct Detection of Wide-Separation Extrasolar Giant Planets
We calculate as a function of orbital distance, mass, and age the theoretical
spectra and orbit-averaged planet/star flux ratios for representative
wide-separation extrasolar giant planets (EGPs) in the optical, near-infrared,
and mid-infrared. Stellar irradiation of the planet's atmosphere and the
effects of water and ammonia clouds are incorporated and handled in a
consistent fashion. We include predictions for 12 specific known EGPs. In the
process, we derive physical diagnostics that can inform the direct EGP
detection and remote sensing programs now being planned or proposed.
Furthermore, we calculate the effects of irradiation on the spectra of a
representative companion brown dwarf as a function of orbital distance.Comment: submitted to the Astrophysical Journal, 19 pages, 11 color figure
The Seeds of Cosmic structure as a door to New Physics
There is something missing in our understanding of the origin of the seeds of
Cosmic Structuture.
The fact that the fluctuation spectrum can be extracted from the inflationary
scenario through an analysis that involves quantum field theory in curved
space-time, and that it coincides with the observational data has lead to a
certain complacency in the community, which prevents the critical analysis of
the obscure spots in the derivation. The point is that the inhomogeneity and
anisotropy of our universe seem to emerge from an exactly homogeneous and
isotropic initial state through processes that do not break those symmetries.
This article gives a brief recount of the problems faced by the arguments based
on established physics, which comprise the point of view held by a large
majority of researchers in the field.
The conclusion is that we need some new physics to be able to fully address
the problem. The article then exposes one avenue that has been used to address
the central issue and elaborates on the degree to which, the new approach makes
different predictions from the standard analyses.
The approach is inspired on Penrose's proposals that Quantum Gravity might
lead to a real, dynamical collapse of the wave function, a process that we
argue has the properties needed to extract us from the theoretical impasse
described above.Comment: Prepared for the proceedings of the conference NEBXII " Recent
Developments in Gravity", Napfio Grece June 2006. LateX, 15 page
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