1,720,985 research outputs found
Reconstruction of the physics of Inflation from next generation cosmological experiments
Full text linkIn this work, we study the problem of the reconstruction of the
physics of inflation using current and future cosmological data from cosmic microwave background and gravitational waves experiments. In particular, we focus on the so-called (supergravity) α-attractor models of inflation constraining the shape of the potential
as well as the reheating properties of the these models. Furthermore, we approach the
problem of the reconstruction of the variation of the inflaton field during inflation providing a next order expression in terms of the inflationary variables
Generating primordial features at large scales in two field models of inflation
Full text linkWe investigate the generation of features at large scales in the primordial power
spectrum (PPS) when inflation is driven by two scalar fields. In canonical single field models
of inflation, these features are often generated due to deviations from the slow-roll regime.
While deviations from slow-roll can be naturally achieved in two field models due to a sharp
turn in the trajectory in the field space, features at the largest scales of the types suggested by
CMB temperature anisotropies are more difficult to achieve in models involving two canonical
scalar fields due to the presence of isocurvature fluctuations. We show instead that a coupling
between the kinetic terms of the scalar fields can easily produce such features. We discuss
models whose theoretical predictions are consistent with current observations and highlight
the implications of our results
Early modified gravity in light of the H 0 tension and LSS data
Full text linkWe present a model of early modified gravity (EMG) consisting in a scalar field σ with a nonminimal coupling to the Ricci curvature of the type Mpl2+ξσ2 plus a cosmological constant and a small effective mass and demonstrate its ability to alleviate the H0 tension while providing a good fit to cosmic microwave background (CMB) anisotropies and baryon acoustic oscillations (BAO) data. In this model the scalar field, frozen deep in the radiation era, grows around the redshift of matter-radiation equality because of the coupling to nonrelativistic matter. The small effective mass, which we consider here as induced by a quartic potential, then damps the scalar field into coherent oscillations around its minimum at σ=0, leading to a weaker gravitational strength at early times and naturally recovering the consistency with laboratory and Solar System tests of gravity. We analyze the capability of EMG with positive ξ to fit current cosmological observations and compare our results to the case without an effective mass and to the popular early dark energy models with ξ=0. We show that EMG with a quartic coupling of the order of λ∼O(eV4/Mpl4) can substantially alleviate the H0 tension also when the full shape of the matter power spectrum is included in the fit in addition to CMB and Supernovae (SN) data
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
Inflation with Violation of the Null Energy Condition
No full textInflation may have been driven by a component which violated the Null-Energy Condition, thereby leading to super inflation. We provide the formalism to study cosmological perturbations when such a component is described by a scalar field with arbitrary Lagrangian. Since the background curvature grows with time, gravitational waves always have a blue spectrum. We apply our formalism to the case of phantom inflation with an exponential potential (whose polelike inflationary stage is an attractor for inhomogeneous cosmological models for any value of the potential slope) as an example. We finally compare the predictions of super inflation with those of standard inflation stressing the role of gravitational waves
Dispelling 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
- …
