1,721,041 research outputs found
Cosmological constraints on the gravitational constant
Full text linkWe study the variation of the gravitational Newton's constant on cosmological
scales in scalar-tensor theories of gravity. We focus on the simplest models of
scalar-tensor theories with a coupling to the Ricci scalar of the form
, such as extended Jordan-Brans-Dicke
(), or a non-minimally coupled scalar field with ,
which permits the gravitational constant to vary self-consistently in time and
space. In addition, we allow the gravitational constant to differ from the
Newton's constant , i.e. . Combining the
information from {\em Planck} 2018 CMB temperature, polarization and lensing,
together with a compilation of BAO measurements from BOSS, we constrain the
imbalance to (68% CL) and the coupling to (95% CL) for JBD and for a non-minimally coupled scalar field we
constrain the imbalance to () and the coupling
parameter to ) both at 95% CL. These constraints
correspond to a variation of the gravitational constant now respect to the one
in the radiation era to be smaller than 3% (95% CL) and to the ratio of the
gravitational Newton's constant measured from cosmological scales and the one
measured in a Cavendish-like experiment to be smaller than 4-15% (95% CL). With
current data, we observe that the degeneracy between , the coupling
, and allows for a larger value of the Hubble constant increasing
the agreement between the measurement of the Hubble constant by the SH0ES team
and its value inferred by CMB data. Future data such as the combination of CMB
anisotropies from LiteBIRD and CMB-S4, and large-scale structures galaxy
clustering from DESI and galaxy shear from LSST will reduce the uncertainty to
.Comment: 33 pages, 18 figures, 6 table
Type Ia supernovae data with scalar-tensor gravity
No full textWe study the use of type Ia supernovae (SNe Ia) in the context of
scalar-tensor theories of gravity, taking as a working example induced gravity,
equivalent to Jordan-Brans-Dicke theory. Winking at accurate and precision
cosmology, we test the correction introduced by a time variation of the
Newton's constant, predicted by scalar-tensor theories, on the SNe distance
modulus relation. We find that for induced gravity the coupling parameter is
constrained from (95\% CL) using Pantheon SNe data alone down to
(95\% CL) in combination with {\em Planck} data release DR3 and
a compilation of baryon acoustic oscillations (BAO) measurements from BOSS
DR12. In this minimal case the improvements in terms of constraints on the
cosmological parameters coming from the addition of SNe data to cosmic
microwave background (CMB) and BAO measurements is limited, on the
95\% CL upper bound on . Allowing for the value of the gravitational
constant today to depart from the Newton constant, we find that the addition of
SNe further tightens the constraints obtained by CMB and BAO data on the
standard cosmological parameters and by 22\% on the coupling parameter, i.e.,
at 95\% CL. We finally show that in this class of modified
gravity models the use a prior on the absolute magnitude in combination
with the Pantheon SNe sample leads to results which are very consistent with
those obtained by imposing a prior on , as happens for other {\em
early-type} models which accommodate a larger value of compared to the
CDM results.Comment: 14 pages, 10 figure
Constraining the neutrino mass using a multitracer combination of two galaxy surveys and cosmic microwave background lensing
Full text linkMeasuring the total neutrino mass is one of the most exciting opportunities available with next-generation cosmological data sets. We study the possibility of detecting the total neutrino mass using large-scale clustering in 21 cm intensity mapping and photometric galaxy surveys, together with cosmic microwave background (CMB) information. We include the scale-dependent halo bias contribution due to the presence of massive neutrinos, and use a multitracer analysis in order to reduce cosmic variance. The multitracer combination of an SKAO-MID 21 cm intensity map with stage 4 CMB dramatically shrinks the uncertainty on total neutrino mass to σ(Mν)≃45 meV, using only linear clustering information (kmax=0.1hMpc−1) and without a prior on optical depth. When we add to the multitracer the clustering information expected from Legacy Survey of Space and Time, the forecast is σ(Mν)≃12 meV
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
Probing primordial features with future galaxy surveys
Full text linkWe study the capability of future measurements of the galaxy clustering power spectrum to probe departures from a power-law spectrum for primordial fluctuations. On considering the information from the galaxy clustering power spectrum up to quasi-linear scales, i.e. κ < 0:1 h Mpc-1, we present forecasts for DESI, Euclid and SPHEREx in combination with CMB measurements. As examples of departures in the primordial power spectrum from a simple power-law, we consider four Planck 2015 best-fits motivated by inflationary models with different breaking of the slow-roll approximation. At present, these four representative models provide an improved fit to CMB temperature anisotropies, although not at statistical significant level. As for other extensions in the matter content of the simplest CDM model, the complementarity of the information in the resulting matter power spectrum expected from these galaxy surveys and in the primordial power spectrum from CMB anisotropies can be effective in constraining cosmological models. We find that the three galaxy surveys can add significant information to CMB to better constrain the extra parameters of the four models considered
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
On the ISW-cluster cross-correlation in future surveys
Full text linkWe acknowledge financial contribution from the agreement ASI n.I/023/12/0 ‘Attivit`a relative alla fase B2/C
per la missione Euclid’. The support by the ‘ASI/INAF Agreement 2014-024-R.0 for the Planck LFI Activity of Phase E2’ is also acknowledged. MB, DP, FF, and LM acknowledge the support from
the grant MIUR PRIN 2015 ‘Cosmology and Fundamental Physics: illuminating the Dark Universe with Euclid’. MB was supported by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Technology and the Claude Leon Foundation. BS acknowledges financial support from the University of Trieste through
the program ‘Finanziamento di Ateneo per progetti di ricerca scientifica – FRA 2015’, a grant from ’Consorzio per la Fisica – Trieste’ and from the PRIN 2015W7KAWC project, funded by the Italian
Minister for University and Research.We investigate the cosmological information contained in the cross-correlation between the integrated Sachs-Wolfe (ISW) of the cosmic microwave background (CMB) anisotropy pattern and galaxy clusters from future wide surveys. Future surveys will provide cluster catalogues with a number of objects comparable with galaxy catalogues currently used for the detection of the ISW signal by cross-correlation with the CMB anisotropy pattern. By computing the angular power spectra of clusters and the corresponding cross-correlation with CMB, we perform a signal-to-noise ratio (SNR) analysis for the ISW detection as expected from the eROSITA and the Euclid space missions. We discuss the dependence of the SNR of the ISW-cluster cross-correlation on the specifications of the catalogues and on the reference cosmology. We forecast that the SNRs for ISW-cluster cross-correlation are slightly smaller compared to those which can be obtained from future galaxy surveys but the signal is expected to be detected at high significance, i.e. more than > 3 σ. We also forecast the joint constraints on parameters of model extensions of the concordance Λ cold dark matter (ΛCDM) cosmology by combining CMB and the ISW-cluster cross-correlation
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
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