1,721,078 research outputs found
Constraining pre Big-Bang-Nucleosynthesis Expansion using Cosmic Antiprotons
No full textA host of dark energy models and non–standard cosmologies predict an enhanced Hubble rate in
the early Universe: perfectly viable models, which satisfy Big Bang Nucleosynthesis (BBN), cosmic
microwave background and general relativity tests, may nevertheless lead to enhancements of the
Hubble rate up to many orders of magnitude. In this paper we show that strong bounds on the pre–
BBN evolution of the Universe may be derived, under the assumption that dark matter is a thermal
relic, by combining the dark matter relic density bound with constraints coming from the production
of cosmic–ray antiprotons by dark matter annihilation in the Galaxy. The limits we derive can be
sizable and apply to the Hubble rate around the temperature of dark matter decoupling. For dark
matter masses lighter than 100 GeV, the bound on the Hubble–rate enhancement ranges from a
factor of a few to a factor of 30, depending on the actual cosmological model, while for a mass of
500 GeV the bound falls in the range 50–500. Uncertainties in the derivation of the bounds and
situations where the bounds become looser are discussed. We finally discuss how these limits apply
to some specific realizations of non–standard cosmologies: a scalar–tensor gravity model, kination
models and a Randall–Sundrum D–brane model
Long-Range Forces in Direct Dark Matter Searches
Full text linkWe discuss the positive indications of a possible dark matter signal in direct detection experiments in terms of a mechanism of interaction between the dark matter particle and the nuclei occurring via the exchange of a light mediator, resulting in a long-range interaction. We analyze the annual modulation results observed by the DAMA and CoGeNT experiments and the observed excess of events of CRESST. In our analysis, we discuss the relevance of uncertainties related to the velocity distribution of galactic dark matter and to the channeling effect in NaI. We find that a long-range force is a viable mechanism, which can provide full agreement between the reconstructed dark matter properties from the various experimental data sets, especially for masses of the light mediator in the 10-30 MeV range and a light dark matter with a mass around 10 GeV. The relevant bounds on the light mediator mass and scattering cross section are then derived, should the annual modulation effects be due to this class of long-range forces
Extending the DAMA annual-modulation region by inclusion of the uncertainties in astrophysical velocities
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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
Nailing Down the Theoretical Uncertainties of D[over ̄] Spectrum Produced from Dark Matter
No full textThe detection of cosmic antideuterons (D]) at kinetic energies below a few GeV/n could provide a smoking gun signature for dark matter (DM). However, the theoretical uncertainties of coalescence models have represented so far one of the main limiting factors for precise predictions of the D[over ̄] flux. In this Letter, we present a novel calculation of the D[over ̄] source spectra, based on the Wigner formalism, for which we implement the Argonne v_{18} antideuteron wave function that does not have any free parameters related to the coalescence process. We show that the Argonne-Wigner model excellently reproduces the D[over ̄] multiplicity measured by ALEPH at the Z-boson pole, which is usually adopted to tune the coalescence models based on different approaches. Our analysis is based on the pythia 8 Monte Carlo event generator and the state-of-the-art shower algorithm. We succeed, with our model, to reduce the current theoretical uncertainty on the prediction of the D[over ̄] source spectra to a few percent, for D[over ̄] kinetic energies relevant to DM searches with the General Antiparticle Spectrometer and Alpha Magnetic Spectrometer, and for DM masses above a few tens of GeV. This result implies that the theoretical uncertainties due to the coalescence process are no longer the main limiting factor in the predictions. We provide the tabulated source spectra for all the relevant DM annihilation and decay channels and DM masses between 5 and 100 TeV, on the CosmiXs GitHub repository
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
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