1,720,982 research outputs found
Not-so-Dark Matter: strategies for indirect detection and identification of Dark Matter
Full text linkThe existence of Dark Matter (DM) is supported by multiple evidences, achieved by means of very different experimental strategies. Its energy density today has been measured to account for almost a quarter of the total energy density in the Universe.
DM is mainly sensible to gravity and it interacts only weakly through nuclear and electromagnetic interactions.
Under the assumption that a DM particle is its own anti-particle, annihilation products can be searched for in order to obtain informations about DM distribution and, more generally, to infer some of its properties. This is the idea beyond DM indirect detection. In this Ph.D. thesis I will focus only on DM annihilation into gamma-rays and discuss the possibility of obtaining clear DM signatures from the analysis of gamma-rays signals.
Being the annihilation flux proportional to the DM density squared, natural targets for indirect searches are the Galactic Center (due to its vicinity and its large amount of DM) and the near dwarf spheroidal galaxies (due to their large mass-to-light ratio). Experimental data from both these classes of sources have not found any clear DM signal, being able only to provide upper limits on the annihilation flux.
I will present here two alternative strategies for which DM signatures may be detected and a signal from annihilation may be disentagled from the gamma-ray background.
In the first case I will focus on the effect that Black Holes (BHs) can have on the distribution of DM producing overdensities. The most efficent mechanism is the adiabatic contraction around SuperMassive Black Holes, able to create large enhancements called spikes. However, the scenario of mini-spikes around Intermediate Mass Black Holes is more realistic and I will present prospects of detecting DM from mini-spikes in our Galaxy and in the Andromeda Galaxy.
I will move then to the analysis of the angular power spectrum of anistropies in the gamma-ray emission. After that the galactic foreground (due to cosmic rays interacting with the Galactic interstellar medium) is subtructed from a map of the gamma-ray sky, a residual isotropic background remains, called Extra-galactic Cosmic Gamma-ray Background (EGB) and measured by EGRET.
The Fermi LAT satellite will soon provide a more precise measurement of the EGB and I will present here predictions showing that the DM can contribution to the EGB flux and that its presence can be detected in the analysis of the angular power spectrum of the EGB. Both Galactic and extra-galactic DM substructures are taken into account, the first dominating the angular spectrum at low multipoles.
This thesis is based on the projects I have been involved in during my Ph.D. and I will mainly present results already discussed in those papers where I am among the authors.L'esistenza della Materia Oscura (MO) e' sostenuta da molteplici
evidenze, ottenute con l'utilizzo di tecniche sperimentali diversificate e complementari. La densita' energetica della MO risulta spiegare quasi un quarto della densita' di energia dell'intero Universo. Essa risente prevalentemente della gravita' interagendo solo debolmente tramite interazioni nucleari ed elettromagnetiche. Seguendo l'ipotesi che la particella di MO sia anche la sua stessa anti-particella, una strategia per ottenere informazioni su come e' distribuita la MO e, piu' in generale per
dedurre alcune delle sue proprieta', e' quella di cercare i suoi prodotti di annichilazione. E' questa l'idea che sta alla base della rivelazione indiretta di MO. Nella presente tesi di dottorato mi limitero' all'annichilazione della MO in raggi gamma e verranno discusse le previsioni per ottenere una chiara segnatura della presenza della MO dall'analisi dei segnali gamma.
Essendo il flusso di annichilazione proporzionale alla densita' di MO al quadrato, gli obiettivi principali della rivelazione indiretta sono il Centro Galattico (a causa della sua vicinanza e della grande quantita' di MO stimata) e le galassie sferoidali nane presenti all'interno della Via Lattea (a causa del loro alto rapporto massa su luce). Gli dati sperimentali attuali provenienti da queste due classi di oggetti, non sono stati in grado di rivelare un chiaro segnale della presenza della MO, ma solamente di fornire dei limiti superiori al flusso di annichilazione. Presentero' in questa tesi due strategie alternative in grado di identificare delle segnature piuttosto chiare della presenza della MO attraverso le quali sara' possibile distinguere il segnale di annichilazione dal fondo gamma. Nel primo caso mi focalizzero' sull'effetto che i buchi neri possono avere sulla distribuzione di MO portando alla formazione di sovra-densita'. Il meccanismo piu' efficente e' quello della contrazione adiabatica attorno ai Buchi Neri SuperMassici, capace di produrre grandi innalzamenti nella densita' di MO chiamate cuspidi. D'altro canto, lo scenario piu' plausibile e' quello delle mini-cuspidi attorno ai Buchi Neri di Massa Intermedia e verranno presentate previsioni per la rivelazione della MO nelle mini-cuspidi della Via Lattea e della galassia di Andromeda. Mi focalizzero poi sulla seconda alternativa, lo studio dello spettro angolare di potenza per le anisotropie nell'emissione gamma. Dopo che il contributo Galattico (dovuto all'interazione dei raggi cosmici con il mezzo interstellare Galattico) e' stato sottratto dai dati di EGRET, un fondo isotropo residuo rimane, chiamato Fondo Extra-galattico Gamma (FEG). Il satellite Fermi LAT fornira' nell'immediato futuro una nuova stima del FEG ed io mostero', negli ultimi capitoli, come la MO possa contribuire al flusso del FEG e come la sua presenza possa essere rivelata nell'analisi del spettro angolare del FEG.
Verranno considerate allo stesso tempo sottostrutture Galattiche ed extra-galattiche, dove le prime constituiscono la componente principale dello spettro angolare a bassi multipoli.
Questa tesi e' basata sui progetti nei quali sono stato coinvolti durante il mio dottorato e presentero' risultati gia' discussi in quei lavori per i quali figuro tra gli autori
Dark matter signals from Draco and Willman 1: prospects for MAGIC II and CTA
No full textThe next generation of ground-based Imaging Air Cherenkov Telescopes will play an important role in indirect dark matter searches. In this article, we consider two particularly promising candidate sources for dark matter annihilation signals, the nearby dwarf galaxies Draco and Willman 1, and study the prospects of detecting such a signal for the soon- operating MAGIC II telescope system as well as for the planned installation of CTA, taking special care of describing the experimental features that affect the detectional prospects. For the first time in such studies, we fully take into account the effect of internal bremsstrahlung, which has recently been shown to considerably enhance, in some cases, the gamma-ray flux in the high energies domain where Atmospheric Cherenkov Telescopes operate, thus leading to significantly harder annihilation spectra than traditionally considered. While the detection of the spectral features introduced by internal bremsstrahlung would constitute a smoking gun signature for dark matter annihilation, we find that for most models the overall flux still remains at a level that will be challenging to detect, unless one adopts somewhat favorable descriptions of the smooth dark matter distribution in the dwarfs
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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