179 research outputs found
Transit timing analysis of CoRoT-1b
CoRoT, the pioneer space-based transit search, steadily provides thousands of
high-precision light curves with continuous time sampling over periods of up to
5 months. The transits of a planet perturbed by an additional object are not
strictly periodic. By studying the transit timing variations (TTVs), additional
objects can be detected in the system.
A transit timing analysis of CoRoT-1b is carried out to constrain the
existence of additional planets in the system.
We used data obtained by an improved version of the CoRoT data pipeline
(version 2.0). Individual transits were fitted to determine the mid-transit
times, and we analyzed the derived diagram. N-body integrations were used
to place limits on secondary planets.
No periodic timing variations with a period shorter than the observational
window (55 days) are found. The presence of an Earth-mass Trojan is not likely.
A planet of mass greater than Earth mass can be ruled out by the
present data if the object is in a 2:1 (exterior) mean motion resonance with
CoRoT-1b. Considering initially circular orbits: (i) super-Earths (less than 10
Earth-masses) are excluded for periods less than about 3.5 days, (ii)
Saturn-like planets can be ruled out for periods less than about 5 days, (iii)
Jupiter-like planets should have a minimum orbital period of about 6.5 days.Comment: 6 pages, accepted at A&
A Stochastic Measure for Eternal Inflation
We use the stochastic approach to investigate the measure for slow roll
eternal inflation. The probability for the universe of a given Hubble radius
can be calculated in this framework. In a solvable model, it is shown that the
probability for the universe to evolve from a state with a smaller Hubble
radius to that of a larger Hubble radius is dominated by the classical
probability without the stochastic source. While the probability for the
universe to evolve from a larger Hubble radius to a smaller one is suppressed
by , where the de Sitter entropy arises naturally in this
stochastic approach.Comment: 11 pages, 1 figur
Budding yeast ATM/ATR control meiotic double-strand break (DSB) levels by down-regulating Rec114, an essential component of the DSB-machinery
An essential feature of meiosis is Spo11 catalysis of programmed DNA double strand breaks (DSBs). Evidence suggests that the number of DSBs generated per meiosis is genetically determined and that this ability to maintain a pre-determined DSB level, or "DSB homeostasis", might be a property of the meiotic program. Here, we present direct evidence that Rec114, an evolutionarily conserved essential component of the meiotic DSB-machinery, interacts with DSB hotspot DNA, and that Tel1 and Mec1, the budding yeast ATM and ATR, respectively, down-regulate Rec114 upon meiotic DSB formation through phosphorylation. Mimicking constitutive phosphorylation reduces the interaction between Rec114 and DSB hotspot DNA, resulting in a reduction and/or delay in DSB formation. Conversely, a non-phosphorylatable rec114 allele confers a genome-wide increase in both DSB levels and in the interaction between Rec114 and the DSB hotspot DNA. These observations strongly suggest that Tel1 and/or Mec1 phosphorylation of Rec114 following Spo11 catalysis down-regulates DSB formation by limiting the interaction between Rec114 and DSB hotspots. We also present evidence that Ndt80, a meiosis specific transcription factor, contributes to Rec114 degradation, consistent with its requirement for complete cessation of DSB formation. Loss of Rec114 foci from chromatin is associated with homolog synapsis but independent of Ndt80 or Tel1/Mec1 phosphorylation. Taken together, we present evidence for three independent ways of regulating Rec114 activity, which likely contribute to meiotic DSBs-homeostasis in maintaining genetically determined levels of breaks
Regular black holes in quadratic gravity
The first-order correction of the perturbative solution of the coupled
equations of the quadratic gravity and nonlinear electrodynamics is
constructed, with the zeroth-order solution coinciding with the ones given by
Ay\'on-Beato and Garc{\'\i}a and by Bronnikov. It is shown that a simple
generalization of the Bronnikov's electromagnetic Lagrangian leads to the
solution expressible in terms of the polylogarithm functions. The solution is
parametrized by two integration constants and depends on two free parameters.
By the boundary conditions the integration constants are related to the charge
and total mass of the system as seen by a distant observer, whereas the free
parameters are adjusted to make the resultant line element regular at the
center. It is argued that various curvature invariants are also regular there
that strongly suggests the regularity of the spacetime. Despite the complexity
of the problem the obtained solution can be studied analytically. The location
of the event horizon of the black hole, its asymptotics and temperature are
calculated. Special emphasis is put on the extremal configuration
Adiabatic and entropy perturbations propagation in a bouncing Universe
By studying some bouncing universe models dominated by a specific class of
hydrodynamical fluids, we show that the primordial cosmological perturbations
may propagate smoothly through a general relativistic bounce. We also find that
the purely adiabatic modes, although almost always fruitfully investigated in
all other contexts in cosmology, are meaningless in the bounce or null energy
condition (NEC) violation cases since the entropy modes can never be neglected
in these situations: the adiabatic modes exhibit a fake divergence that is
compensated in the total Bardeen gravitational potential by inclusion of the
entropy perturbations.Comment: 25 pages, no figure, LaTe
The Raychaudhuri equations: a brief review
We present a brief review on the Raychaudhuri equations. Beginning with a
summary of the essential features of the original article by Raychaudhuri and
subsequent work of numerous authors, we move on to a discussion of the
equations in the context of alternate non--Riemannian spacetimes as well as
other theories of gravity, with a special mention on the equations in
spacetimes with torsion (Einstein--Cartan--Sciama--Kibble theory). Finally, we
give an overview of some recent applications of these equations in General
Relativity, Quantum Field Theory, String Theory and the theory of relativisitic
membranes. We conclude with a summary and provide our own perspectives on
directions of future research.Comment: 35 pages, two figures, to appear in the special issue of Pramana
dedicated to the memory of A. K. Raychaudhur
Transiting exoplanets from the CoRoT space mission I - CoRoT-Exo-1b: a low-density short-period planet around a G0V star
Context. The pioneer space mission for photometric planet searches, CoRoT,
steadily monitors about 12,000 stars in each of its fields of view; it is able
to detect transit candidates early in the processing of the data and before the
end of a run. Aims. We report the detection of the first planet discovered by
CoRoT and characterizing it with the help of follow-up observations. Methods.
Raw data were filtered from outliers and residuals at the orbital period of the
satellite. The orbital parameters and the radius of the planet were estimated
by best fitting the phase folded light curve with 34 successive transits.
Doppler measurements with the SOPHIE spectrograph permitted us to secure the
detection and to estimate the planet mass. Results. The accuracy of the data is
very high with a dispersion in the 2.17 min binned phase-folded light curve
that does not exceed 3.10-4 in flux unit. The planet orbits a mildly metal-poor
G0V star of magnitude V=13.6 in 1.5 days. The estimated mass and radius of the
star are 0.95+-0.15Msun and 1.11+-0.05Rsun. We find the planet has a radius of
1.49+-0.08Rjup, a mass of 1.03+-0.12Mjup, and a particularly low mean density
of 0.38 +-0.05g cm-3.Comment: A&A letters (in press) - 4 pages - 3 figure
Can the Universe Create Itself?
The question of first-cause has troubled philosophers and cosmologists alike.
Now that it is apparent that our universe began in a Big Bang explosion, the
question of what happened before the Big Bang arises. Inflation seems like a
very promising answer, but as Borde and Vilenkin have shown, the inflationary
state preceding the Big Bang must have had a beginning also. Ultimately, the
difficult question seems to be how to make something out of nothing. This paper
explores the idea that this is the wrong question --- that that is not how the
Universe got here. Instead, we explore the idea of whether there is anything in
the laws of physics that would prevent the Universe from creating itself.
Because spacetimes can be curved and multiply connected, general relativity
allows for the possibility of closed timelike curves (CTCs). Thus, tracing
backwards in time through the original inflationary state we may eventually
encounter a region of CTCs giving no first-cause. This region of CTCs, may well
be over by now (being bounded toward the future by a Cauchy horizon). We
illustrate that such models --- with CTCs --- are not necessarily inconsistent
by demonstrating self-consistent vacuums for Misner space and a multiply
connected de Sitter space in which the renormalized energy-momentum tensor does
not diverge as one approaches the Cauchy horizon and solves Einstein's
equations. We show such a Universe can be classically stable and
self-consistent if and only if the potentials are retarded, giving a natural
explanation of the arrow of time. Some specific scenarios (out of many possible
ones) for this type of model are described. For example: an inflationary
universe gives rise to baby universes, one of which turns out to be itself.
Interestingly, the laws of physics may allow the Universe to be its own mother.Comment: 48 pages, 8 figure
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Baryon Oscillation Spectroscopic Survey of SDSS-III
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the
scale of baryon acoustic oscillations (BAO) in the clustering of matter over a
larger volume than the combined efforts of all previous spectroscopic surveys
of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as
i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7.
Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000
quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5.
Early results from BOSS include the first detection of the large-scale
three-dimensional clustering of the Lyman alpha forest and a strong detection
from the Data Release 9 data set of the BAO in the clustering of massive
galaxies at an effective redshift z = 0.57. We project that BOSS will yield
measurements of the angular diameter distance D_A to an accuracy of 1.0% at
redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the
same redshifts. Forecasts for Lyman alpha forest constraints predict a
measurement of an overall dilation factor that scales the highly degenerate
D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey
is complete. Here, we provide an overview of the selection of spectroscopic
targets, planning of observations, and analysis of data and data quality of
BOSS.Comment: 49 pages, 16 figures, accepted by A
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