480 research outputs found
Games judges don’t play: predatory pricing and strategic reasoning in US antitrust
The paper analyzes the last three decades of debates about predatory pricing in US antitrust law, starting from the literature which followed Areeda and Turner’s 1975 paper and ending in the beginning of this century, upon the Brooke 1993 decision. Special emphasis is given to the game-theoretic approach to predation and to the reasons why this approach has never gained attention in the courtroom. It is argued that, despite their mathematical rigor, the sophisticated stories told by strategic models in order to demonstrate the actual viability of predatory behavior fail to satisfy the criteria which guide the decisions of antitrust courts, in particular their preference for easy-to-apply rules. Therefore, predation cases are still governed by a peculiar alliance between Chicago-style price theory – which, contrary to game theory, considers predatory behavior almost always irrational – and a Harvard-style attention to the operational side of antitrust enforcement
A PCA-based automated finder for galaxy-scale strong lenses
We present an algorithm using Principal Component Analysis (PCA) to subtract
galaxies from imaging data, and also two algorithms to find strong,
galaxy-scale gravitational lenses in the resulting residual image. The combined
method is optimized to find full or partial Einstein rings. Starting from a
pre-selection of potential massive galaxies, we first perform a PCA to build a
set of basis vectors. The galaxy images are reconstructed using the PCA basis
and subtracted from the data. We then filter the residual image with two
different methods. The first uses a curvelet (curved wavelets) filter of the
residual images to enhance any curved/ring feature. The resulting image is
transformed in polar coordinates, centered on the lens galaxy center. In these
coordinates, a ring is turned into a line, allowing us to detect very faint
rings by taking advantage of the integrated signal-to-noise in the ring (a line
in polar coordinates). The second way of analysing the PCA-subtracted images
identifies structures in the residual images and assesses whether they are
lensed images according to their orientation, multiplicity and elongation. We
apply the two methods to a sample of simulated Einstein rings, as they would be
observed with the ESA Euclid satellite in the VIS band. The polar coordinates
transform allows us to reach a completeness of 90% and a purity of 86%, as soon
as the signal-to-noise integrated in the ring is higher than 30, and almost
independent of the size of the Einstein ring. Finally, we show with real data
that our PCA-based galaxy subtraction scheme performs better than traditional
subtraction based on model fitting to the data. Our algorithm can be developed
and improved further using machine learning and dictionary learning methods,
which would extend the capabilities of the method to more complex and diverse
galaxy shapes
The metallicity distribution of the halo and the satellites of the Milky way in the hierarchical merging paradigm
To account for the observed differential metallicity distribution (DMD) of
the Milky Way halo, a semi-analytical model is presented in the framework of
the hierarchical merging paradigm for structure formation. It is assumed that
the Milky Way halo is composed of a number of sub-haloes with properties either
as observed in the dwarf satellite galaxies of the Local group (shape of
metallicity distribution, effective yield) or derived from calculations of
structure formation (sub-halo distribution function). With reasonable
assumptions for the parameters involved, we find that the overall shape and
effective yield of the Galactic halo DMD can be reproduced in the framework of
such a simple model. The low metallicity tail of the DMD presents a defficiency
of stars with respect to the simple model predictions (akin to the G-dwarf
problem in the solar neighborhood); it is suggested that an early infall phase
can account for that problem, as well as for the observed DMDs of dwarf
satellite galaxies.Accretion of galaxies similar (but not identical) to the
progenitors of present day dwarf satellites of the Milky Way may well have
formed the Galactic halo.Comment: 10 pages, 6 fig. to appear in Astronomy and Astrophysic
Truth or precision? Some reflections on the economists’ failure to predict the financial crisis
The failure of professional economic forecasters to predict the financial crises has led many to question the credibility of modern economics as a reliable foundation for economic policy. If economists were unable to foresee so big a crisis, how can they be trusted to cure or prevent it? Several accounts of this failure exist. The paper offers a tentative answer based on the lessons that may be drawn from the wisdom of a short list of past and present economists: Hayek, Neville Keynes, Mankiw, Tinbergen, Maynard Keynes and Lucas. The glue to keep such an odd bunch together is the distinction between truth and precision provided by science historian Ted Porter
The MUSIC of CLASH: predictions on the concentration-mass relation
We present the results of a numerical study based on the analysis of the
MUSIC-2 simulations, aimed at estimating the expected concentration-mass
relation for the CLASH cluster sample. We study nearly 1400 halos simulated at
high spatial and mass resolution, which were projected along many
lines-of-sight each. We study the shape of both their density and
surface-density profiles and fit them with a variety of radial functions,
including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the
Einasto density profiles. We derive concentrations and masses from these fits
and investigate their distributions as a function of redshift and halo
relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra
observations of the halos and we use them to identify objects resembling the
X-ray morphologies and masses of the clusters in the CLASH X-ray selected
sample. We also derive a concentration-mass relation for strong-lensing
clusters. We find that the sample of simulated halos which resemble the X-ray
morphology of the CLASH clusters is composed mainly by relaxed halos, but it
also contains a significant fraction of un-relaxed systems. For such a sample
we measure an average 2D concentration which is ~11% higher than found for the
full sample of simulated halos. After accounting for projection and selection
effects, the average NFW concentrations of CLASH clusters are expected to be
intermediate between those predicted in 3D for relaxed and super-relaxed halos.
Matching the simulations to the individual CLASH clusters on the basis of the
X-ray morphology, we expect that the NFW concentrations recovered from the
lensing analysis of the CLASH clusters are in the range [3-6], with an average
value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray
morphologies similar to those of the CLASH clusters are affected by a modest
orientation bias.Comment: 21 pages, 16 figures, 3 tables, submitted to Ap
Bailing Out the Milky Way: Variation in the Properties of Massive Dwarfs Among Galaxy-Sized Systems
Recent kinematical constraints on the internal densities of the Milky Way's
dwarf satellites have revealed a discrepancy with the subhalo populations of
simulated Galaxy-scale halos in the standard CDM model of hierarchical
structure formation. This has been dubbed the "too big to fail" problem, with
reference to the improbability of large and invisible companions existing in
the Galactic environment. In this paper, we argue that both the Milky Way
observations and simulated subhalos are consistent with the predictions of the
standard model for structure formation. Specifically, we show that there is
significant variation in the properties of subhalos among distinct host halos
of fixed mass and suggest that this can reasonably account for the deficit of
dense satellites in the Milky Way. We exploit well-tested analytic techniques
to predict the properties in a large sample of distinct host halos with a
variety of masses spanning the range expected of the Galactic halo. The
analytic model produces subhalo populations consistent with both Via Lactea II
and Aquarius, and our results suggest that natural variation in subhalo
properties suffices to explain the discrepancy between Milky Way satellite
kinematics and these numerical simulations. At least ~10% of Milky Way-sized
halos host subhalo populations for which there is no "too big to fail" problem,
even when the host halo mass is as large as M_host = 10^12.2 h^-1 M_sun.
Follow-up studies consisting of high-resolution simulations of a large number
of Milky Way-sized hosts are necessary to confirm our predictions. In the
absence of such efforts, the "too big to fail" problem does not appear to be a
significant challenge to the standard model of hierarchical formation.
[abridged]Comment: 12 pages, 3 figures; accepted by JCAP. Replaced with published
versio
Dark energy with gravitational lens time delays
Strong lensing gravitational time delays are a powerful and cost effective
probe of dark energy. Recent studies have shown that a single lens can provide
a distance measurement with 6-7 % accuracy (including random and systematic
uncertainties), provided sufficient data are available to determine the time
delay and reconstruct the gravitational potential of the deflector.
Gravitational-time delays are a low redshift (z~0-2) probe and thus allow one
to break degeneracies in the interpretation of data from higher-redshift probes
like the cosmic microwave background in terms of the dark energy equation of
state. Current studies are limited by the size of the sample of known lensed
quasars, but this situation is about to change. Even in this decade, wide field
imaging surveys are likely to discover thousands of lensed quasars, enabling
the targeted study of ~100 of these systems and resulting in substantial gains
in the dark energy figure of merit. In the next decade, a further order of
magnitude improvement will be possible with the 10000 systems expected to be
detected and measured with LSST and Euclid. To fully exploit these gains, we
identify three priorities. First, support for the development of software
required for the analysis of the data. Second, in this decade, small robotic
telescopes (1-4m in diameter) dedicated to monitoring of lensed quasars will
transform the field by delivering accurate time delays for ~100 systems. Third,
in the 2020's, LSST will deliver 1000's of time delays; the bottleneck will
instead be the aquisition and analysis of high resolution imaging follow-up.
Thus, the top priority for the next decade is to support fast high resolution
imaging capabilities, such as those enabled by the James Webb Space Telescope
and next generation adaptive optics systems on large ground based telescopes.Comment: White paper submitted to SNOWMASS201
Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes
International audienceOn March 15th 2007 a paroxysmal explosion occurred at the Stromboli volcano. This event generated a large amount of products, mostly lithic blocks, some of which impacted the ground as far as down to 200 m a.s.l., about 1.5 km far away from the active vents. Two days after the explosion, a new vapour emission was discovered on the north-eastern flank of the volcanic edifice, at 560 m a.s.l., just above the area called "Nel Cannestrà ". This new vapour emission was due to a block impact. In order to investigate the block impact area to understand the appearance of the vapour emission, we conducted on May 2008 a multidisciplinary study involving Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Self-Potential (SP), CO2 soil diffuse degassing and soil temperature surveys. This complementary data set revealed the presence of an anomalous conductive body, probably related to a shallow hydrothermal level, at about 10-15 m depth, more or less parallel to the topography. It is the first time that such a hydrothermal fluid flow, with a temperature close to the water boiling point (76 °C) has been evidenced at Stromboli at this low elevation on the flank of the edifice. The ERT results suggest a possible link between (1) the main central hydrothermal system of Stromboli, located just above the plumbing system feeding the active vents, with a maximum of subsurface soil temperature close to 90 °C and limited by the NeoStromboli summit crater boundary and (2) the investigated area of Nel Cannestrà , at ~ 500 m a.s.l., a buried eruptive fissure active 9 ka ago. In parallel, SP and CO2 soil diffuse degassing measurements suggest in this sector at slightly lower elevation from the block impact crater a magmatic and hydrothermal fluid rising system along the N41° regional fault. A complementary ERT profile, on May 2009, carried out from the NeoStromboli crater boundary down to the block impact crater displayed a flank fluid flow apparently connected to a deeper system. The concept of shallow hydrothermal level have been compared to similar ERT results recently obtained on Mount Etna and La Fossa cone of Vulcano. This information needs to be taken into account in general fluid flow models on volcanoes. In particular, peripheral thermal waters (as those bordering the north-eastern coast of Stromboli) could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit
Euclid preparation. XXVIII. Forecasts for ten different higher-order weak lensing statistics
Recent cosmic shear studies have shown that higher-order statistics (HOS) developed by independent teams now outperform standard two-point estimators in terms of statistical precision thanks to their sensitivity to the non-Gaussian features of large-scale structure. The aim of the Higher-Order Weak Lensing Statistics (HOWLS) project is to assess, compare, and combine the constraining power of ten different HOS on a common set of Euclid-like mocks, derived from N-body simulations. In this first paper of the HOWLS series, we computed the nontomographic (Ω, σ) Fisher information for the one-point probability distribution function, peak counts, Minkowski functionals, Betti numbers, persistent homology Betti numbers and heatmap, and scattering transform coefficients, and we compare them to the shear and convergence two-point correlation functions in the absence of any systematic bias. We also include forecasts for three implementations of higher-order moments, but these cannot be robustly interpreted as the Gaussian likelihood assumption breaks down for these statistics. Taken individually, we find that each HOS outperforms the two-point statistics by a factor of around two in the precision of the forecasts with some variations across statistics and cosmological parameters. When combining all the HOS, this increases to a 4.5 times improvement, highlighting the immense potential of HOS for cosmic shear cosmological analyses with Euclid. The data used in this analysis are publicly released with the paper
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