1,721,315 research outputs found
CMB acoustic scale in the entropic-like accelerating universe
No full textWe consider generalizations of the entropic accelerating universe recently proposed in [D. A. Easson, P. H. Frampton, and G. F. Smoot, Phys. Lett. B 696, 273 (2011).] and [D. A. Easson, P. H. Frampton, and G. F. Smoot, arXiv:1003.1528.] and show that their background equations can be made equivalent to a model with a dark energy component with a constant parameter of state wX=-1+2γ/3, where γ is related to the coefficients of the new terms in the Friedmann equations. After discussing all the Friedmann equations for an arbitrary γ, we show how to recover the standard scalings for dust and radiation. The acoustic scale ℓA, related to the peak positions in the pattern of the angular power spectrum of the cosmic microwave background anisotropies, is also computed and yields the stringent bound |γ|≪1. We then argue that future data might be able to distinguish this model from pure ΛCDM (corresponding to γ=0)
Light Bending as a Probe of the Nature of Dark Energy
No full textWe study the bending of light for static spherically symmetric (SSS) space-times which include a dark energy contribution. Geometric dark energy models generically predict a correction to the Einstein angle written in terms of the distance to the closest approach, whereas a cosmological constant does not.
While dark energy is associated with a repulsive force in cosmological context, its effect on null geodesics in SSS space-times can be attractive as for the Newtonian term. This dark energy contribution may not be negligible with respect to the Einstein prediction in lensing involving clusters of galaxies. Strong lensing may therefore be useful to distinguish from other dark energy models
Testing discrete symmetries with the cosmic microwave background: current constraints and Planck forecasts
No full textAnisotropy and polarization of the CMB are probing cosmological models with unprecedented precision. The WMAP satellite data are largely consistent with concordance ACDM cosmology. However, intriguing flukes are known to exist that may pinpoint at physics beyond the standard model. Constraining the violations of discrete symmetries in the CMB pattern is a promising mean to investigate these discrepancies. In this paper we constrain the Parity and CPT symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon. Finally, we provide forecasts for Planck and we discuss how emission from a specific diffuse foreground component arising within the Solar System needs to be kept under strict control to avoid incurring into false positive detections
Boundaries and the Casimir effect in noncommutative space-time
No full textWe calculate modifications to the scalar Casimir force between two parallel plates due to space-time noncommutativity. We devise a heuristic approach to overcome the difficulties of describing boundaries in noncommutative theories and predict that boundary corrections are of the same order as noncommutative volume corrections. Further, both corrections have the form of more conventional finite surface effects
The Planck Mission: Recent Results, Cosmological and Fundamental Physics Perspectives
No full textWe provide a description of the latest status and performance of the Planck satellite, focusing on the final predicted sensitivity of Planck. The optimization of the observational strategy for the additional surveys following the nominal 15 months of integration (about two surveys) originally allocated and the limitation represented by astrophysical foreground emissions are presented. An outline of early and intermediate astrophysical results from the Planck Collaboration is provided. A concise view of some fundamental cosmological results that will be achieved by exploiting Planck's full set of temperature and polarization data are presented. Finally, the perspectives opened by Planck in answering some key questions in fundamental physics, with particular attention to parity symmetry analyses, are described
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
The Planck mission: From first results to cosmology
Full text linkPlanck is a ESA satellite, currently in operation, whose main objective is to accurately image the anisotropies of the Cosmic Microwave Background Radiation in intensity and polarization. Benefiting from an unprecedented combination
of sensitivity, angular resolution, and frequency leverage, Planck will provide high quality data to be mined in cosmology and astrophysics. The first Planck results have been released in January 2011 and include both Galactic and extragalactic source catalogues, a list of galaxy clusters selected by the Sunyaev-Zel’dovich effect, and a cold cores catalogue. The first cosmological data products are awaited for early 2013. Planck has a wide list of scientific targets. Here we focus on one specific aspect which is also of interest to the high energy physics community: constraining the Parity and CPT symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide
marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon
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