1,301 research outputs found
On prospects for dark matter indirect detection in the Constrained MSSM
In the framework of the Constrained MSSM we derive the most probable ranges of the diffuse gamma radiation flux from the direction of the Galactic center and of the positron flux from the Galactic halo due to neutralino dark matter annihilation. We find that, for a given halo model, and assuming flat priors, the 68% probability range of the integrated gamma-ray flux spans about one order of magnitude, while the 95% probability range can be much larger and extend over four orders of magnitude (even exceeding five for a tiny region at small neutralino mass). The detectability of the signal by GLAST depending primarily on the cuspiness of the halo profile. The positron flux, on the other hand, appears to be too small to be detectable by PAMELA, unless the boost factor is at least of order ten and/or the halo profile is extremely cuspy. We also briefly discuss the sensitivity of our results to the choice of priors
Directional Detection of Dark Matter with MIMAC
Directional detection is a promising search strategy to discover galactic
Dark Matter. We present a Bayesian analysis framework dedicated to Dark Matter
phenomenology using directional detection. The interest of directional
detection as a powerful tool to set exclusion limits, to authentify a Dark
Matter detection or to constrain the Dark Matter properties, both from particle
physics and galactic halo physics, will be demonstrated. However, such results
need highly accurate track reconstruction which should be reachable by the
MIMAC detector using a dedicated readout combined with a likelihood analysis of
recoiling nuclei.Comment: 4 pages, 2 figures, to appear in the proceedings of the TAUP 2011
conference held in Munich (5 - 9 September, 2011
The power of Bayesian evidence in astronomy
We discuss the use of the Bayesian evidence ratio, or Bayes factor, for model
selection in astronomy. We treat the evidence ratio as a statistic and
investigate its distribution over an ensemble of experiments, considering both
simple analytical examples and some more realistic cases, which require
numerical simulation. We find that the evidence ratio is a noisy statistic, and
thus it may not be sensible to decide to accept or reject a model based solely
on whether the evidence ratio reaches some threshold value. The odds suggested
by the evidence ratio bear no obvious relationship to the power or Type I error
rate of a test based on the evidence ratio. The general performance of such
tests is strongly affected by the signal to noise ratio in the data, the
assumed priors, and the threshold in the evidence ratio that is taken as
`decisive'. The comprehensiveness of the model suite under consideration is
also very important. The usefulness of the evidence ratio approach in a given
problem can be assessed in advance of the experiment, using simple models and
numerical approximations. In many cases, this approach can be as informative as
a much more costly full-scale Bayesian analysis of a complex problem.Comment: 11 pages; MNRAS in pres
Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots
The development of scalable sources of non-classical light is fundamental to unlocking thetechnological potential of quantum photonics. Semiconductor quantum dots are emerging asnear-optimal sources of indistinguishable single photons. However, their performance assources of entangled-photon pairs are still modest compared to parametric down converters.Photons emitted from conventional Stranski–Krastanov InGaAs quantum dots have shownnon-optimal levels of entanglement and indistinguishability. For quantum networks, bothcriteria must be met simultaneously. Here, we show that this is possible with a system thathas received limited attention so far: GaAs quantum dots. They can emit triggered polar-ization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguish-ability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity(0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dotentanglement sources in future quantum technologie
Neutrinos and Future Concordance Cosmologies
We review the free parameters in the concordance cosmology, and those which
might be added to this set as the quality of astrophysical data improves. Most
concordance parameters encode information about otherwise unexplored aspects of
high energy physics, up to the GUT scale via the "inflationary sector," and
possibly even the Planck scale in the case of dark energy. We explain how
neutrino properties may be constrained by future astrophysical measurements.
Conversely, future neutrino physics experiments which directly measure these
parameters will remove uncertainty from fits to astrophysical data, and improve
our ability to determine the global properties of our universe.Comment: Proceedings of paper given at Neutrino 2008 meeting (by RE
Measuring the effective complexity of cosmological models
We introduce a statistical measure of the effective model complexity, called
the Bayesian complexity. We demonstrate that the Bayesian complexity can be
used to assess how many effective parameters a set of data can support and that
it is a useful complement to the model likelihood (the evidence) in model
selection questions. We apply this approach to recent measurements of cosmic
microwave background anisotropies combined with the Hubble Space Telescope
measurement of the Hubble parameter. Using mildly non-informative priors, we
show how the 3-year WMAP data improves on the first-year data by being able to
measure both the spectral index and the reionization epoch at the same time. We
also find that a non-zero curvature is strongly disfavored. We conclude that
although current data could constrain at least seven effective parameters, only
six of them are required in a scheme based on the Lambda-CDM concordance
cosmology.Comment: 9 pages, 4 figures, revised version accepted for publication in PRD,
updated with WMAP3 result
Engineering of quantum dot photon sources via electro-elastic fields
The possibility to generate and manipulate non-classical light using the
tools of mature semiconductor technology carries great promise for the
implementation of quantum communication science. This is indeed one of the main
driving forces behind ongoing research on the study of semiconductor quantum
dots. Often referred to as artificial atoms, quantum dots can generate single
and entangled photons on demand and, unlike their natural counterpart, can be
easily integrated into well-established optoelectronic devices. However, the
inherent random nature of the quantum dot growth processes results in a lack of
control of their emission properties. This represents a major roadblock towards
the exploitation of these quantum emitters in the foreseen applications. This
chapter describes a novel class of quantum dot devices that uses the combined
action of strain and electric fields to reshape the emission properties of
single quantum dots. The resulting electro-elastic fields allow for control of
emission and binding energies, charge states, and energy level splittings and
are suitable to correct for the quantum dot structural asymmetries that usually
prevent these semiconductor nanostructures from emitting polarization-entangled
photons. Key experiments in this field are presented and future directions are
discussed.Comment: to appear as a book chapter in a compilation "Engineering the
Atom-Photon Interaction" published by Springer in 2015, edited by A.
Predojevic and M. W. Mitchel
Bayesian analysis of Friedmannless cosmologies
Assuming only a homogeneous and isotropic universe and using both the 'Gold'
Supernova Type Ia sample of Riess et al. and the results from the Supernova
Legacy Survey, we calculate the Bayesian evidence of a range of different
parameterizations of the deceleration parameter. We consider both spatially
flat and curved models. Our results show that although there is strong evidence
in the data for an accelerating universe, there is little evidence that the
deceleration parameter varies with redshift.Comment: 7 pages, 3 figure
Flat Tree-level Inflationary Potentials in Light of CMB and LSS Data
We use cosmic microwave background and large scale structure data to test a
broad and physically well-motivated class of inflationary models: those with
flat tree-level potentials (typical in supersymmetry). The non-trivial features
of the potential arise from radiative corrections which give a simple
logarithmic dependence on the inflaton field, making the models very
predictive. We also consider a modified scenario with new physics beyond a
certain high-energy cut-off showing up as non-renormalizable operators (NRO) in
the inflaton field. We find that both kinds of models fit remarkably well CMB
and LSS data, with very few free parameters. Besides, a large part of these
models naturally predict a reasonable number of e-folds. A robust feature of
these scenarios is the smallness of tensor perturbations (r < 10^{-3}). The NRO
case can give a sizeable running of the spectral index while achieving a
sufficient number of e-folds. We use Bayesian model comparison tools to assess
the relative performance of the models. We believe that these scenarios can be
considered as a standard physical class of inflationary models, on a similar
footing with monomial potentials.Comment: 42 LaTeX pages, 8 figure
Genotyping-by-sequencing resolves relationships in Polygonaceae tribe Eriogoneae
The resolution of cryptic diversity is essential for understanding the evolutionary diversification of lineages and establishing conservation priorities. We examine relationships in Eriogoneae (Polygonaceae), a diverse lineage in western North America. We ask whether Eriogonum umbellatum, a morphologically and ecologically diverse species, is monophyletic and whether its varieties represent evolutionary lineages. We use genotyping-by-sequencing to assemble a SNP dataset for 51 species in the genera Chorizanthe, Eriogonum and Sidotheca. We report a hierarchical phylogenetic analysis using maximum likelihood to estimate the evolutionary history of Eriogoneae. We illustrate admixture components for 21 populations of E. umbellatum, representing four varieties, and test for lineage structure using TreeMix. We identify strongly supported clades within Eriogoneae. Many relationships in the Eucycla + Oregonium and Latifolia clades are supported, while most relationships within the Eriogonum subg. Oligogonum clade and a clade with most Chorizanthe remain unresolved. Eriogonum congdonii resolves within the main E. umbellatum clade, while populations of three varieties of E. umbellatum are closely related to E. ursinum and are associated with serpentine soils. ADmixture and TreeMix analyses suggest E. umbellatum varieties represent evolutionary lineages. These results from SNP data are largely consistent with previous phylogenetic studies of Eriogoneae based on sequence variation. Structure within Oligogonum suggests consistent environmental association and radiation after initial colonization of serpentine. Morphology is unreliable for the infraspecific taxonomy of E. umbellatum. Additional molecular studies are needed to resolve the evolutionary relationships and ecological diversification within this species, in Oligogonum, and in Eriogoneae. © 2021 The Authors. TAXON published by John Wiley & Sons Ltd on behalf of International Association for Plant Taxonomy.We thank SGIker research support services at the University of the Basque Country, Leioa, Spain for DNA extraction and quality control, and acknowledge Centro Nacional de d-An?lisi Gen?mica in Barcelona, Spain for GBS sequencing. We thank J. Andre, N.J. Jensen and J. Steele for contributing samples and D. Marino for collaboration in nucleic acid extractions. We acknowledge the contributions of O. Lao Grueso to the?ADmixture and TreeMix analyses. We thank U.S. Forest Service employees D. Austin, J. Fedorchuk, M. Friend, J. Haas, D. Ikeda, L. Janeway, J. Nelson, D. Netz, A. Sanger, and S. Weis among others for facilitating permitting and collecting. This work was supported by funds from the Basque Government in support of the Terrestrial Plant Diversity group of the Department of Plant Biology and Ecology, University of the Basque Country, and an ERC Advanced Grant, FP7-IDEAS-ERC, ?ADAPT?, project 339941 awarded to T. Brown. We thank SGIker research support services at the University of the Basque Country, Leioa, Spain for DNA extraction and quality control, and acknowledge Centro Nacional de d‐Anàlisi Genòmica in Barcelona, Spain for GBS sequencing. We thank J. Andre, N.J. Jensen and J. Steele for contributing samples and D. Marino for collaboration in nucleic acid extractions. We acknowledge the contributions of O. Lao Grueso to the ADmixture and TreeMix analyses. We thank U.S. Forest Service employees D. Austin, J. Fedorchuk, M. Friend, J. Haas, D. Ikeda, L. Janeway, J. Nelson, D. Netz, A. Sanger, and S. Weis among others for facilitating permitting and collecting. This work was supported by funds from the Basque Government in support of the Terrestrial Plant Diversity group of the Department of Plant Biology and Ecology, University of the Basque Country, and an ERC Advanced Grant, FP7‐IDEAS‐ERC, ‘ADAPT’, project 339941 awarded to T. Brown
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