1,720,969 research outputs found
Pre-heating in the framework of massive gravity
No full textAbstractIn this paper we propose a mechanism of natural pre-heating of our universe by introducing an inflaton field dependent mass term for the gravitational wave for a specific class of massive gravity theory. For any single field inflationary model, the inflaton must go through the oscillatory phase after the end of inflation. As has recently been pointed out, if the gravitational fluctuation has inflaton dependent mass term, there will be a resonant amplification of the amplitude of the gravitational wave during the oscillatory phase of inflaton. Because of this large enhancement of the amplitude of the gravitational wave due to parametric resonance, we show that universe can naturally go through the pre-reheated phase with minimally coupled matter field. Therefore, during the reheating phase, there is no need to introduce any arbitrary coupling between the matter field and the inflaton
Minimal Higgs inflation
No full textIn this paper we propose minimal Higgs inflation scenarios by non-polynomial modification of the Higgs potential. The modification is done in such a way that it creates a flat plateau for a huge range of field values at the inflationary energy scale μ≃(λ)1/4α. Assuming the perturbative Higgs quartic coupling, λ≃O(1), our model prediction for all the cosmologically relevant quantities, (ns,r,dnsk), fit extremely well with observations made by PLANCK. For both the models the inflation energy scale turned out to be μ≃(1014,1015) GeV. Considering observed central value of the scalar spectral index, ns=0.968, models predict efolding number, N=(52,47). Within a wide range of viable parameter space, we found that the prediction of tensor to scalar ratio r(≤10−5) is far below the current experimental limit. The prediction for the running of scalar spectral index, dnsk, remains very small. We also computed the background field dependent unitarity scale Λ(h), which turned out to be much larger than the aforementioned inflationary energy scale
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Superradiant scattering of electromagnetic fields from ringing black holes
No full textAbstract Detection of gravitational waves (GWs) paves the beginning of a new era of gravitational wave astronomy. Black holes (BHs) in their ringdown phase (ringing BHs) provide the cleanest signal of emitted GWs that imprint the fundamental nature of BHs under low energy perturbation. Apart from GWs, any complementary signature of ringing BHs can be of paramount importance. Motivated by this, we analyzed the scattering of electromagnetic waves in such a background and demonstrated that the absorption cross section of a ringing Schwarzschild BH can be superradiant. It appears that superradiance in the ringdown phase results from the stimulated growth of the matter field, driven by the oscillating gravitational background. Therefore, the amplification is inherently transient, with a characteristic time scale equal to the GW oscillation time scale. We have further analysed the frequency ranges of such amplified transient signals for a wide range of BH masses. In this context, we propose the premise that the primordial black hole (PBH) may undergo a merging phase and exhibit superradiance. We point out that the existing ground-based Low Frequency Array (LOFAR), radio telescopes could be able to detect such transient signals from PBHs, with mass range M ∼ 10 - 1 - 10 - 2 M ⊙ , going through the ringdown phase. Our present result, therefore, opens up an intriguing possibility of observing the PBH-PBH merging phenomena through electromagnetic waves
Constraining parity and charge-parity violating varying-alpha theory through laboratory experiments
No full textDispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
