18,009 research outputs found
Cosmic microwave background constraints on cosmological models with large-scale isotropy breaking
Several anomalies appear to be present in the large-angle cosmic microwave
background (CMB) anisotropy maps of WMAP, including the alignment of
large-scale multipoles. Models in which isotropy is spontaneously broken (e.g.,
by a scalar field) have been proposed as explanations for these anomalies, as
have models in which a preferred direction is imposed during inflation. We
examine models inspired by these, in which isotropy is broken by a
multiplicative factor with dipole and/or quadrupole terms. We evaluate the
evidence provided by the multipole alignment using a Bayesian framework,
finding that the evidence in favor of the model is generally weak. We also
compute approximate changes in estimated cosmological parameters in the
broken-isotropy models. Only the overall normalization of the power spectrum is
modified significantly.Comment: Accepted for publication in Phys. Rev.
Determination of the intrinsic Luminosity Time Correlation in the X-ray Afterglows of GRBs
Gamma-ray bursts (GRBs), which have been observed up to redshifts z approx
9.5 can be good probes of the early universe and have the potential of testing
cosmological models. The analysis by Dainotti of GRB Swift afterglow
lightcurves with known redshifts and definite X-ray plateau shows an
anti-correlation between the rest frame time when the plateau ends (the plateau
end time) and the calculated luminosity at that time (or approximately an
anti-correlation between plateau duration and luminosity). We present here an
update of this correlation with a larger data sample of 101 GRBs with good
lightcurves. Since some of this correlation could result from the redshift
dependences of these intrinsic parameters, namely their cosmological evolution
we use the Efron-Petrosian method to reveal the intrinsic nature of this
correlation. We find that a substantial part of the correlation is intrinsic
and describe how we recover it and how this can be used to constrain physical
models of the plateau emission, whose origin is still unknown. The present
result could help clarifing the debated issue about the nature of the plateau
emission.Comment: Astrophysical Journal accepte
Strange quark suppression from a simultaneous Monte Carlo analysis of parton distributions and fragmentation functions
We perform the first simultaneous extraction of unpolarized parton
distributions and fragmentation functions from a Monte Carlo analysis of
inclusive and semi-inclusive deep-inelastic scattering, Drell-Yan lepton-pair
production, and single-inclusive annihilation data. We use data
resampling techniques to thoroughly explore the Bayesian posterior distribution
of the extracted functions, and use -means clustering on the parameter
samples to identify the configurations that give the best description across
all reactions. Inclusion of the semi-inclusive data reveals a strong
suppression of the strange quark distribution at parton momentum fractions , in contrast with the ATLAS observation of enhanced strangeness
in and production at the LHC. Our study reveals significant
correlations between the strange quark density and the strange kaon
fragmentation function needed to simultaneously describe semi-inclusive
production data from COMPASS and inclusive spectra in
annihilation from ALEPH and SLD, as well as between the strange and light
antiquark densities in the proton.Comment: 6 pages, 4 figures; version to appear in Phys. Rev.
Oddification of the cohomology of type A Springer varieties
We identify the ring of odd symmetric functions introduced by Ellis and
Khovanov as the space of skew polynomials fixed by a natural action of the
Hecke algebra at q=-1. This allows us to define graded modules over the Hecke
algebra at q=-1 that are `odd' analogs of the cohomology of type A Springer
varieties. The graded module associated to the full flag variety corresponds to
the quotient of the skew polynomial ring by the left ideal of nonconstant odd
symmetric functions. The top degree component of the odd cohomology of Springer
varieties is identified with the corresponding Specht module of the Hecke
algebra at q=-1.Comment: 21 pages, 2 eps file
Partial orders on partial isometries
This paper studies three natural pre-orders of increasing generality on the
set of all completely non-unitary partial isometries with equal defect indices.
We show that the problem of determining when one partial isometry is less than
another with respect to these pre-orders is equivalent to the existence of a
bounded (or isometric) multiplier between two natural reproducing kernel
Hilbert spaces of analytic functions. For large classes of partial isometries
these spaces can be realized as the well-known model subspaces and
deBranges-Rovnyak spaces. This characterization is applied to investigate
properties of these pre-orders and the equivalence classes they generate.Comment: 30 pages. To appear in Journal of Operator Theor
Age of Information in Multicast Networks with Multiple Update Streams
We consider the age of information in a multicast network where there is a
single source node that sends time-sensitive updates to receiver nodes.
Each status update is one of two kinds: type I or type II. To study the age of
information experienced by the receiver nodes for both types of updates, we
consider two cases: update streams are generated by the source node at-will and
update streams arrive exogenously to the source node. We show that using an
earliest and transmission scheme for type I and type II updates,
respectively, the age of information of both update streams at the receiver
nodes can be made a constant independent of . In particular, the source node
transmits each type I update packet to the earliest and each type II
update packet to the earliest of receiver nodes. We determine the
optimum and stopping thresholds for arbitrary shifted exponential
link delays to individually and jointly minimize the average age of both update
streams and characterize the pareto optimal curve for the two ages
Slavery is bad for business: analyzing the impact of slavery on national economies
Public discourse on human trafficking and modern-day slavery is reaching a tipping point -- it is coming to be understood as a global problem with economic and policy implications far beyond simple reports of cross-border human trafficking. A decade ago most educated citizens considered slavery a phenomenon of the past, relegated to history textbooks. Today a strong narrative has reached global proportions: activists, epistemic communities, NGOs, IGOs, and governments are acknowledging the scope and extent of slavery in the twenty-first century. One need only point to Nicholas Kristof and Sheryl Wu Dunn’s bestseller Half the Sky, President Barack Obama’s 2012 speech at the Clinton Global Intiative, or the awareness that celebrities such as Mira Sorvino and Jada Pinkett Smith are raising about the subject to illustrate how far the antislavery movement has progressed.1 Yet despite such civic mindedness, surprisingly little data and empirically driven research exist on slavery today. Although some headway has been made in estimating its prevalence -- most notably in the form of contributions by Kevin Bales and by the International Labor Organization (ILO) -- apart from a rough estimate of how many slaves exist in the world today (21 to 27 million), scholars and policy makers know little about the risk factors -- let alone the business impact -- that contemporary slavery has on the global community.2 Indeed, most extant research, although useful, is qualitative, not allowing for statistical models.3 To what extent is slavery empirically bad for business? For whom is the business of slavery profitable, and for whom is it economically burdensome
Bandwidth in bolometric interferometry
Bolometric Interferometry is a technology currently under development that
will be first dedicated to the detection of B-mode polarization fluctuations in
the Cosmic Microwave Background. A bolometric interferometer will have to take
advantage of the wide spectral detection band of its bolometers in order to be
competitive with imaging experiments. A crucial concern is that interferometers
are presumed to be importantly affected by a spoiling effect known as bandwidth
smearing. In this paper, we investigate how the bandwidth modifies the work
principle of a bolometric interferometer and how it affects its sensitivity to
the CMB angular power spectra. We obtain analytical expressions for the
broadband visibilities measured by broadband heterodyne and bolometric
interferometers. We investigate how the visibilities must be reconstructed in a
broadband bolometric interferometer and show that this critically depends on
hardware properties of the modulation phase shifters. Using an angular power
spectrum estimator accounting for the bandwidth, we finally calculate the
sensitivity of a broadband bolometric interferometer. A numerical simulation
has been performed and confirms the analytical results. We conclude (i) that
broadband bolometric interferometers allow broadband visibilities to be
reconstructed whatever the kind of phase shifters used and (ii) that for
dedicated B-mode bolometric interferometers, the sensitivity loss due to
bandwidth smearing is quite acceptable, even for wideband instruments (a factor
2 loss for a typical 20% bandwidth experiment).Comment: 13 pages, 14 figures, submitted to A&
Real complex functions
We survey a few classes of analytic functions on the disk that have real
boundary values almost everywhere on the unit circle. We explore some of their
properties, various decompositions, and some connections these functions make
to operator theory.Comment: 44 page
Aliens, the Internet, and Purposeful Availment : A Reassessment of Fifth Amendment Limits on Personal Jurisdiction
This Article first considers the Fourteenth Amendment cases and argues that the constitutional limits on the jurisdictional authority of state courts reflect a view about the limits of state authority. It then turns to the Fifth Amendment and, after considering the practices of other nations and lessons from prescriptive jurisdiction, argues that the United States\u27s sovereign authority should allow it to assert personal jurisdiction solely on the basis of effects in the United States, without a requirement of purposeful availment. It further argues that concerns about reasonableness should be addressed at the subconstitutional level. This Article is built on two basic premises: that personal jurisdiction is a doctrine that concerns the allocation of sovereign authority, and that the underlying sovereignty considerations of the United States within the world community are quite different from those of the states within our confederation of states. As a result, although the Due Process Clauses of the Fifth and Fourteenth Amendments are worded the same, the limitations that those clauses impose on sovereign authority are different
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