1,720,972 research outputs found
Cosmological Implications of Gravitational Wave Observations
No full textGWs are a very powerful probe to understand the Universe and provide a unique way to study its evolution. First, the direct detection of gravitational waves by the LVK collaboration, and more recently the claim from Pulsar Timing Array collaborations, have further confirmed the potential of these signals. In this thesis we explore the cosmological implications associated to GW detections focusing mainly on primordial NG and on the Hubble parameter . After introducing GWs and primordial NG, we study the imprints of local NG on the SIGW spectrum. Hence, we forecast the capability of LISA to detect NG, finding that it could be constrained up to the percent level. In the context of SIGW, we assume that the PTA signal can be attributed to SIGWs, while considering various possible shapes for the scalar power spectrum. We find upper bounds on the amplitude of the scalar power spectrum that we use to constrain the abundance of PBHs in the stellar mass range. We then study the impact on the abundance due to the presence of primordial local NG, finding that it could also exclude PBHs.
Then, we consider different imprints of primordial NG, considering its signatures on the tracer bias, with the tracers being GW sources contributing to an astrophysical background of GWs. After characterizing the anisotropies of the signal, we evaluate their cross-correlation with the Cosmic Microwave Background ones to forecast the capability of future interferometers to detect the imprint of NG on the largest scales.
Finally, we focus on resolved GWs, in the context of dark sirens combined with a galaxy catalog, to constrain the Hubble parameter. We study the presence of possible biases due to a mismodelling of the galaxy host probability, finding that mismatching the redshift or the luminosity dependence could induce different biases towards higher or lower values of , spoiling the inference.
Thus, in this thesis, we show with different examples that GWs, whether originating in the early Universe or in more recent times and both of astrophysical and cosmological origin, represent an important tool to probe the Universe
Non-Gaussianity from the Cross-correlation of the Astrophysical Gravitational Wave Background and the Cosmic Microwave Background
Full text linkSince the first LIGO/Virgo detection, Gravitational Waves (GWs) have been
very promising as a new complementary probe to understand our Universe. One of
the next challenges of GW search is the detection and characterization of the
stochastic gravitational wave background (SGWB), that is expected to open a
window on the very early Universe (cosmological background) and to provide us
new information on astrophysical source populations (astrophysical background).
One way to characterize the SGWB and to extract information about its origin is
through the cross-correlation with other cosmological probes. To this aim, in
this paper, we explore the cross-correlation between the astrophysical
background anisotropies and the Cosmic Microwave Background (CMB) ones. Such a
signal is sensitive to primordial non-Gaussianity (nG) through the GW bias.
Thus, we study the capability of next generation space-based interferometers to
detect such a cross-correlation signal and to constrain primordial nG.Comment: 13 pages, 5 figures - Matched the published versio
Fully non-Gaussian Scalar-Induced Gravitational Waves
Full text linkScalar -Induced Gravitational Waves (SIGWs) represent a particular class of primordial signals which are sourced at second -order in perturbation theory whenever a scalar fluctuation of the metric is present. They form a guaranteed Stochastic Gravitational Wave Background (SGWB) that, depending on the amplification of primordial scalar fluctuations, can be detected by GW detectors. The amplitude and the frequency shape of the scalar -induced SGWB can be influenced by the statistical properties of the scalar density perturbations. In this work we study the intuitive physics behind SIGWs and we analyze the imprints of local non-Gaussianity of the primordial curvature perturbation on the GW spectrum. We consider all the relevant non -Gaussian contributions up to fifth -order in the scalar seeds without any hierarchy, and we derive the related GW energy density ohm GW ( f ). We perform a Fisher matrix analysis to understand to which accuracy non-Gaussianity can be constrained with the LISA detector, which will be sensitive in the milli -Hertz frequency band. We find that LISA, neglecting the impact of astrophysical foregrounds, will be able to measure the amplitude, the width and the peak of the spectrum with an accuracy up to O(10 - 4 ), while non-Gaussianity can be measured up to O(10 - 3 ). Finally, we discuss the implications of our non-Gaussianity expansion on the fraction of Primordial Black Holes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Investigation of Piezoelectret Properties of 3D Printed Foamed Polylactic Acid for Energy Conversion Applications
No full textDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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