315 research outputs found
Benchmark Parameters for CMB Polarization Experiments
The recently detected polarization of the cosmic microwave background (CMB)
holds the potential for revealing the physics of inflation and gravitationally
mapping the large-scale structure of the universe, if so called B-mode signals
below 10^{-7}, or tenths of a uK, can be reliably detected. We provide a
language for describing systematic effects which distort the observed CMB
temperature and polarization fields and so contaminate the B-modes. We identify
7 types of effects, described by 11 distortion fields, and show their
association with known instrumental systematics such as common mode and
differential gain fluctuations, line cross-coupling, pointing errors, and
differential polarized beam effects. Because of aliasing from the small-scale
structure in the CMB, even uncorrelated fluctuations in these effects can
affect the large-scale B modes relevant to gravitational waves. Many of these
problems are greatly reduced by having an instrumental beam that resolves the
primary anisotropies (FWHM << 10'). To reach the ultimate goal of an
inflationary energy scale of 3 \times 10^{15} GeV, polarization distortion
fluctuations must be controlled at the 10^{-2}-10^{-3} level and temperature
leakage to the 10^{-4}-10^{-3} level depending on effect. For example pointing
errors must be controlled to 1.5'' rms for arcminute scale beams or a percent
of the Gaussian beam width for larger beams; low spatial frequency differential
gain fluctuations or line cross-coupling must be eliminated at the level of
10^{-4} rms.Comment: 11 pages, 5 figures, submitted to PR
Perturbation evolution with a non-minimally coupled scalar field
We recently proposed a simple dilaton-derived quintessence model in which the
scalar field was non-minimally coupled to cold dark matter, but not to
`visible' matter. Such couplings can be attributed to the dilaton in the low
energy limit of string theory, beyond tree level. In this paper we discuss the
implications of such a model on structure formation, looking at its impact on
matter perturbations and CMB anisotropies. We find that the model only deviates
from CDM and minimally coupled theories at late times, and is well
fitted to current observational data. The signature left by the coupling, when
it breaks degeneracy at late times, presents a valuable opportunity to
constrain non-minimal couplings given the wealth of new observational data
promised in the near future.Comment: Version appearing in Physical Review D. 10 pages, 9 figs. Comparison
with SN1a and projected MAP results, and appendix adde
Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical properties
New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in
presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene
catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which
are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote
an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within
the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic
process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting
endotherm. These results indicate that polyethylene macrochains can grow up during polymerization
either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements.
Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the
crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the
nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is
raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the
final processing temperature
Double Inflation in Supergravity and the Large Scale Structure
The cosmological implication of a double inflation model with hybrid + new
inflations in supergravity is studied. The hybrid inflation drives an inflaton
for new inflation close to the origin through supergravity effects and new
inflation naturally occurs. If the total e-fold number of new inflation is
smaller than , both inflations produce cosmologically relevant density
fluctuations. Both cluster abundances and galaxy distributions provide strong
constraints on the parameters in the double inflation model assuming
standard cold dark matter scenario. The future satellite
experiments to measure the angular power spectrum of the cosmic microwave
background will make a precise determination of the model parameters possible.Comment: 19 pages (RevTeX file
Inflationary Cosmology with Five Dimensional SO(10)
We discuss inflationary cosmology in a five dimensional SO(10) model
compactified on , which yields below the compactification scale. The gauge
symmetry is preserved on one of the fixed points, while
``flipped'' is on the other fixed point. Inflation is
associated with breaking, and is implemented through -term scalar
potentials on the two fixed points. A brane-localized Einstein-Hilbert term
allows both branes to have positive tensions during inflation. The scale of
breaking is fixed from measurements to be around
GeV, and the scalar spectral index . The inflaton field
decays into right-handed neutrinos whose subsequent out of equilibrium decay
yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in
PR
Multiple drivers of decline in the global status of freshwater crayfish (Decapoda: Astacidea)
International audienceRates of biodiversity loss are higher in freshwater ecosystems than in most terrestrial or marine ecosystems, making freshwater conservation a priority. However, prioritization methods are impeded by insufficient knowledge on the distribution and conservation status of freshwater taxa, particularly invertebrates. We evaluated the extinction risk of the world's 590 freshwater crayfish species using the IUCN Categories and Criteria and found 32% of all species are threatened with extinction. The level of extinction risk differed between families, with proportionally more threatened species in the Parastacidae and Astacidae than in the Cambaridae. Four described species were Extinct and 21% were assessed as Data Deficient. There was geographical variation in the dominant threats affecting the main centres of crayfish diversity. The majority of threatened US and Mexican species face threats associated with urban development, pollution, damming and water management. Conversely, the majority of Australian threatened species are affected by climate change, harvesting, agriculture and invasive species. Only a small proportion of crayfish are found within the boundaries of protected areas, suggesting that alternative means of long-term protection will be required. Our study highlights many of the significant challenges yet to come for freshwater biodiversity unless conservation planning shifts from a reactive to proactive approach
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
The integrated Sachs-Wolfe Effect -- Large Scale Structure Correlation
We discuss the correlation between late-time integrated Sachs-Wolfe (ISW)
effect in the cosmic microwave background (CMB) temperature anisotropies and
the large scale structure of the local universe. This correlation has been
proposed and studied in the literature as a probe of the dark energy and its
physical properties. We consider a variety of large scale structure tracers
suitable for a detection of the ISW effect via a cross-correlation. In addition
to luminous sources, we suggest the use of tracers such as dark matter halos or
galaxy clusters. A suitable catalog of mass selected halos for this purpose can
be constructed with upcoming wide-field lensing and Sunyaev-Zel'dovich (SZ)
effect surveys. With multifrequency data, the presence of the ISW-large scale
structure correlation can also be investigated through a cross-correlation of
the frequency cleaned SZ and CMB maps. While convergence maps constructed from
lensing surveys of the large scale structure via galaxy ellipticities are less
correlated with the ISW effect, lensing potentials that deflect CMB photons are
strongly correlated and allow, probably, the best mechanism to study the
ISW-large scale structure correlation with CMB data alone.Comment: 10 Pages, PRD submitte
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