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  • Oxford University Press  (19)
  • 1
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    Extreme value statistics of cosmic microwave background lensing deflection angles (2015)
    Oxford University Press
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    Publication Date: 2015-08-15
    Description: The smaller the angular scales on which the anisotropies of the cosmic microwave background (CMB) are probed the more important their distortion due to gravitational lensing becomes. Here we investigate the maxima and minima of the CMB lensing deflection field using general extreme value statistics. Since general extreme value statistics applies to uncorrelated data in first place, we consider appropriately low-pass-filtered deflection maps. Besides the suppression of correlations filtering is required for another reason: the lensing field itself is not directly observable but needs to be (statistically) reconstructed from the lensed CMB by means of a quadratic estimator. This reconstruction, though, is noise dominated and therefore requires smoothing too. In idealized Gaussian realizations as well as in realistically reconstructed data, we find that both maxima and minima of the deflection angle components follow consistently a general extreme value distribution of Weibull type. However, its shape, location and scale parameters vary significantly between different realizations. The statistics’ potential power to constrain cosmological models appears, therefore, rather limited.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Intrinsic ellipticity correlations of galaxies: models, likelihoods and interplay with weak lensing (2013)
    Oxford University Press
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    Publication Date: 2013-09-17
    Description: Subject of this paper is the statistical properties of ellipticity alignments between galaxies evoked by their coupled angular momenta. Starting from physical angular momentum models, we bridge the gap towards ellipticity correlations, ellipticity spectra and derived quantities such as aperture moments, comparing the intrinsic signals with those generated by gravitational lensing, with the projected galaxy sample of Euclid in mind. We investigate the dependence of intrinsic ellipticity correlations on cosmological parameters and show that intrinsic ellipticity correlations give rise to non-Gaussian likelihoods as a result of non-linear functional dependences. Comparing intrinsic ellipticity spectra to weak lensing spectra we quantify the magnitude of their contaminating effect on the estimation of cosmological parameters and find that biases on dark energy parameters are very small in an angular momentum-based model in contrast to the linear alignment model commonly used. Finally, we quantify whether intrinsic ellipticities can be measured in the presence of the much stronger weak lensing induced ellipticity correlations, if prior knowledge on a cosmological model is assumed.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 3
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    Cross-bispectra and trispectra of the non-linear integrated Sachs-Wolfe effect and the tracer galaxy density field (2013)
    Oxford University Press
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    Publication Date: 2013-03-02
    Description: In order to investigate possibilities to measure non-Gaussian signatures of the non-linear integrated Sachs–Wolfe (iSW) effect, we study in this work the family of mixed bispectra 〈 q 3 – q 〉 and trispectra 〈 q 4 – q 〉 between the iSW temperature perturbation and the galaxy overdensity . We use standard Eulerian perturbation theory restricted to tree-level expansion for predicting the cosmic matter field. As expected, the spectra are found to decrease in amplitude with increasing q . The transition scale between linear domination and the scales, on which non-linearities take over, moves to larger scales with increasing number of included iSW source fields q . We derive the cumulative signal-to-noise ratios for a combination of Planck cosmic microwave background data and the galaxy sample of a Euclid -like survey. Including scales down to max = 1000 we find sobering values of ~= 0.83 for the mixed bispectrum and ~= 0.19 in the case of the trispectrum for q = 1. For higher values of q , the polyspectra 〈 2 〉 and 〈 3 〉 are found to be far below the detection limit.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 4
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    Born-corrections to weak lensing of the cosmic microwave background temperature and polarization anisotropies (2015)
    Oxford University Press
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    Publication Date: 2015-10-02
    Description: Many weak-lensing calculations make use of the Born approximation where the light ray is approximated by a straight path. We examine the effect of Born-corrections for lensing of the cosmic microwave background (CMB) in an analytical approach by taking perturbative corrections to the geodesic into account. The resulting extra power in the lensing potential spectrum is comparable to the power generated by non-linear structure formation and affects especially the polarization spectra, leading to relative changes of the order of 10 –3 for the E -mode spectrum and several per cent on all scales to the B -mode spectrum. In contrast, there is only little change of spectra involving the CMB temperature. Additionally, the corrections excite one more degree of freedom resulting in a deflection component which cannot be described as a gradient of the lensing potential as it is related to image rotation in lens–lens coupling. We estimate the magnitude of this effect on the CMB spectra and find it to be negligible.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 5
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    Preferred analysis methods for single genomic regions in RNA sequencing revealed by processing the shape of coverage (2012)
    Oxford University Press
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    Publication Date: 2012-05-13
    Description: The informational content of RNA sequencing is currently far from being completely explored. Most of the analyses focus on processing tables of counts or finding isoform deconvolution via exon junctions. This article presents a comparison of several techniques that can be used to estimate differential expression of exons or small genomic regions of expression, based on their coverage function shapes. The problem is defined as finding the differentially expressed exons between two samples using local expression profile normalization and statistical measures to spot the differences between two profile shapes. Initial experiments have been done using synthetic data, and real data modified with synthetically created differential patterns. Then, 160 pipelines (5 types of generator x 4 normalizations x 8 difference measures) are compared. As a result, the best analysis pipelines are selected based on linearity of the differential expression estimation and the area under the ROC curve. These platform-independent techniques have been implemented in the Bioconductor package rnaSeqMap. They point out the exons with differential expression or internal splicing, even if the counts of reads may not show this. The areas of application include significant difference searches, splicing identification algorithms and finding suitable regions for QPCR primers.
    Keywords: Computational Methods, Massively Parallel (Deep) Sequencing, Genomics
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 6
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    A theoretical estimate of intrinsic ellipticity bispectra induced by angular momenta alignments (2014)
    Oxford University Press
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    Publication Date: 2014-10-23
    Description: Intrinsically aligned galaxy shapes are one of the most important systematics in cosmic shear measurements. So far, theoretical studies of intrinsic alignments almost exclusively focus on their statistics at the two-point level. Results from numerical simulations, however, suggest that third-order measures might be even stronger affected. We therefore investigate the (angular) bispectrum of intrinsic alignments. In our fully analytical study, we describe intrinsic galaxy ellipticities by a physical alignment model, which makes use of tidal torque theory. We derive expressions for the various combinations of intrinsic and gravitationally induced ellipticities, i.e. III -, GII - and GGI -alignments, and compare our results to the shear bispectrum, the GGG -term. The latter is computed using hyperextended perturbation theory. Considering equilateral and squeezed configurations, we find that for a Euclid -like survey intrinsic alignments ( III -alignments) start to dominate on angular scales smaller than 20 and 13 arcmin, respectively. This sensitivity to the configuration-space geometry may allow us to exploit the cosmological information contained in both the intrinsic and gravitationally induced ellipticity field. On smallest scales ( ~ 3000), III -alignments exceed the lensing signal by at least one order of magnitude. The amplitude of the GGI -alignments is the weakest. It stays below that of the shear field on all angular scales irrespective of the wavevector configuration.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 7
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    A theoretical estimate of intrinsic ellipticity bispectra induced by angular momenta alignments (2014)
    Oxford University Press
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    Publication Date: 2014-10-24
    Description: Intrinsically aligned galaxy shapes are one of the most important systematics in cosmic shear measurements. So far, theoretical studies of intrinsic alignments almost exclusively focus on their statistics at the two-point level. Results from numerical simulations, however, suggest that third-order measures might be even stronger affected. We therefore investigate the (angular) bispectrum of intrinsic alignments. In our fully analytical study, we describe intrinsic galaxy ellipticities by a physical alignment model, which makes use of tidal torque theory. We derive expressions for the various combinations of intrinsic and gravitationally induced ellipticities, i.e. III -, GII - and GGI -alignments, and compare our results to the shear bispectrum, the GGG -term. The latter is computed using hyperextended perturbation theory. Considering equilateral and squeezed configurations, we find that for a Euclid -like survey intrinsic alignments ( III -alignments) start to dominate on angular scales smaller than 20 and 13 arcmin, respectively. This sensitivity to the configuration-space geometry may allow us to exploit the cosmological information contained in both the intrinsic and gravitationally induced ellipticity field. On smallest scales ( ~ 3000), III -alignments exceed the lensing signal by at least one order of magnitude. The amplitude of the GGI -alignments is the weakest. It stays below that of the shear field on all angular scales irrespective of the wavevector configuration.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 8
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    Contributions to the non-linear integrated Sachs-Wolfe effect: Birkinshaw-Gull effect and gravitational self-energy density (2013)
    Oxford University Press
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    Publication Date: 2013-04-26
    Description: In this paper, we recompute contributions to the spectrum of the non-linear integrated Sachs–Wolfe (iSW)/Rees–Sciama effect in a dark energy cosmology. Focusing on the moderate non-linear regime, all dynamical fields involved are derived from the density contrast in Eulerian perturbation theory. Shape and amplitude of the resulting angular power spectrum are similar to that derived in previous work. With our purely analytical approach we identify two distinct contributions to the signal of the non-linear iSW effect: the change of the gravitational self-energy density of the large-scale structure with (conformal) time and gravitational lenses moving with the large-scale matter stream. In the latter we recover the Birkinshaw–Gull effect. As the non-linear iSW effect itself is inherently hard to detect, observational discrimination between its individual contributions is almost excluded. Our analysis, however, yields valuable insights into the theory of the non-linear iSW effect as a post-Newtonian relativistic effect on propagating photons.
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    Topics: Physics
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  • 9
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    A test of the Suyama-Yamaguchi inequality from weak lensing (2014)
    Oxford University Press
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    Publication Date: 2014-06-12
    Description: We investigate the weak lensing signature of primordial non-Gaussianities of the local type by constraining the magnitude of the weak convergence bi- and trispectra expected for the Euclid weak lensing survey. Starting from expressions for the weak convergence spectra, bispectra and trispectra, whose relative magnitudes we investigate as a function of scale, we compute their respective signal-to-noise ratios by relating the polyspectra's amplitude to their Gaussian covariance using a Monte Carlo technique for carrying out the configuration space integrations. In computing the Fisher matrix on the non-Gaussianity parameters f NL , g NL and NL with a very similar technique, we can derive pieces of Bayesian evidence for a violation of the Suyama–Yamaguchi (SY) relation NL  ≥ (6 f NL /5) 2 as a function of the true f NL - and NL -values and show that the relation can be probed down to levels of f NL  ~= 10 2 and NL  ~= 10 5 . In a related study, we derive analytical expressions for the probability density that the SY relation is exactly fulfilled, as required by models in which any one field generates the perturbations. We conclude with an outlook on the levels of non-Gaussianity that can be probed with tomographic lensing surveys.
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    Topics: Physics
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  • 10
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    Intrinsic alignments and 3d weak gravitational lensing (2013)
    Oxford University Press
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    Publication Date: 2013-08-18
    Description: In this paper we show how intrinsic alignments can be incorporated consistently in the formalism of 3 d weak lensing. We use two different descriptions of the intrinsic galaxy ellipticities, the so-called linear and quadratic model, respectively. For both models we derive the covariance matrix of the intrinsic alignment signal ( II -alignments) and GI -alignments (the cross-correlation of intrinsic and lensing induced ellipticities). Evaluating the covariance matrices for the linear model numerically and comparing the results to the cosmic shear signal we find that for a low-redshift survey the total covariance matrix is dominated by the contributions of the II -alignments. For a Euclid -like survey II -alignments still dominate over GI -alignments but they are more than one order of magnitude smaller than the lensing signal. The shape of the ellipticity covariance matrices is quite different in the k  – k ' -plane for cosmic shear on the one hand and intrinsic alignments on the other hand. In comparison to lensing both alignment types tend to be rather elongated along the diagonal k  = k ' . Moreover, for high multipoles ( ~ 100) intrinsic alignments are strongly concentrated along that diagonal.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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