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Institution

International School for Advanced Studies

EducationTrieste, Friuli-Venezia Giulia, Italy
About: International School for Advanced Studies is a education organization based out in Trieste, Friuli-Venezia Giulia, Italy. It is known for research contribution in the topics: Galaxy & Dark matter. The organization has 3751 authors who have published 13433 publications receiving 588454 citations. The organization is also known as: SISSA & Scuola Internazionale Superiore di Studi Avanzati.


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Journal ArticleDOI
TL;DR: In this paper, it was shown that disformal transformations play a similar role to that of conformal transformations for scalar-tensor theories a l\`a Brans-Dicke.
Abstract: The Horndeski action is the most general one involving a metric and a scalar field that leads to second-order field equations in four dimensions. Being the natural extension of the well-known scalar-tensor theories, its structure and properties are worth analyzing along the experience accumulated in the latter context. Here, we argue that disformal transformations play, for the Horndeski theory, a similar role to that of conformal transformations for scalar-tensor theories a l\`a Brans--Dicke. We identify the most general transformation preserving second-order field equations and discuss the issue of viable frames for this kind of theory, in particular, the possibility to cast the action in the so-called Einstein frame. Interestingly, we find that only for a subset of the Horndeski Lagrangian such a frame exists. Finally, we investigate the transformation properties of such frames under field redefinitions and frame transformations and their reciprocal relationship.

267 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented numerical results of three-dimensional simulations for the merger of binary neutron stars in full general relativity, where hybrid equations of state were adopted to mimic realistic nuclear equations of states.
Abstract: We present numerical results of three-dimensional simulations for the merger of binary neutron stars in full general relativity. Hybrid equations of state are adopted to mimic realistic nuclear equations of state. In this approach, we divide the equations of state into two parts as $P={P}_{\mathrm{cold}}+{P}_{\mathrm{th}}$. ${P}_{\mathrm{cold}}$ is the cold part for which we assign a fitting formula for realistic equations of state of cold nuclear matter slightly modifying the formula developed by Haensel and Potekhin. We adopt the SLy and FPS equations of state for which the maximum allowed Arnowitt-Deser-Misner (ADM) mass of cold and spherical neutron stars is $\ensuremath{\approx}2.04{M}_{\ensuremath{\bigodot}}$ and $1.80{M}_{\ensuremath{\bigodot}}$, respectively. ${P}_{\mathrm{th}}$ denotes the thermal part which is written as ${P}_{\mathrm{th}}=({\ensuremath{\Gamma}}_{\mathrm{th}}\ensuremath{-}1)\ensuremath{\rho}(\ensuremath{\epsilon}\ensuremath{-}{\ensuremath{\epsilon}}_{\mathrm{cold}})$, where $\ensuremath{\rho}$, $\ensuremath{\epsilon}$, ${\ensuremath{\epsilon}}_{\mathrm{cold}}$, and ${\ensuremath{\Gamma}}_{\mathrm{th}}$ are the baryon rest-mass density, total specific internal energy, specific internal energy of the cold part, and the adiabatic constant, respectively. Simulations are performed for binary neutron stars of the total ADM mass in the range between $2.4{M}_{\ensuremath{\bigodot}}$ and $2.8{M}_{\ensuremath{\bigodot}}$ with the rest-mass ratio ${Q}_{M}$ to be in the range $0.9\ensuremath{\lesssim}{Q}_{M}\ensuremath{\le}1$. It is found that if the total ADM mass of the system is larger than a threshold ${M}_{\mathrm{thr}}$, a black hole is promptly formed in the merger irrespective of the mass ratios. In the other case, the outcome is a hypermassive neutron star of a large ellipticity, which results from the large adiabatic index of the realistic equations of state adopted. The value of ${M}_{\mathrm{thr}}$ depends on the equation of state: ${M}_{\mathrm{thr}}\ensuremath{\sim}2.7{M}_{\ensuremath{\bigodot}}$ and $\ensuremath{\sim}2.5{M}_{\ensuremath{\bigodot}}$ for the SLy and FPS equations of state, respectively. Gravitational waves are computed in terms of a gauge-invariant wave extraction technique. In the formation of the hypermassive neutron star, quasiperiodic gravitational waves of a large amplitude and of frequency between 3 and 4 kHz are emitted. The estimated emission time scale is $\ensuremath{\lesssim}100\text{ }\text{ }\mathrm{ms}$, after which the hypermassive neutron star collapses to a black hole. Because of the long emission time, the effective amplitude may be large enough to be detected by advanced laser interferometric gravitational wave detectors if the distance to the source is smaller than $\ensuremath{\sim}100\text{ }\text{ }\mathrm{Mpc}$. Thermal properties of the outcome formed after the merger are also analyzed to approximately estimate the neutrino emission energy.

267 citations

Journal ArticleDOI
R. Adam1, Peter A. R. Ade2, Nabila Aghanim3, Monique Arnaud4  +304 moreInstitutions (71)
TL;DR: In this article, the authors presented foreground-reduced cosmic microwave background (CMB) maps derived from the full Planck data set in both temperature and polarization, and compared to the corresponding Planck 2013 temperature sky maps, the total data volume is larger by a factor of 3.
Abstract: We present foreground-reduced cosmic microwave background (CMB) maps derived from the full Planck data set in both temperature and polarization. Compared to the corresponding Planck 2013 temperature sky maps, the total data volume is larger by a factor of 3.2 for frequencies between 30 and 70 GHz, and by 1.9 for frequencies between 100 and 857 GHz. In addition, systematic errors in the forms of temperature-to-polarization leakage, analogue-to-digital conversion uncertainties, and very long time constant errors have been dramatically reduced, to the extent that the cosmological polarization signal may now be robustly recovered on angular scales l ≳ 40. On the very largest scales, instrumental systematic residuals are still non-negligible compared to the expected cosmological signal, and modes with l< 20 are accordingly suppressed in the current polarization maps by high-pass filtering. As in 2013, four different CMB component separation algorithms are applied to these observations, providing a measure of stability with respect to algorithmic and modelling choices. The resulting polarization maps have rms instrumental noise ranging between 0.21 and 0.27μK averaged over 55′ pixels, and between 4.5 and 6.1μK averaged over pixels. The cosmological parameters derived from the analysis of temperature power spectra are in agreement at the 1σ level with the Planck 2015 likelihood. Unresolved mismatches between the noise properties of the data and simulations prevent a satisfactory description of the higher-order statistical properties of the polarization maps. Thus, the primary applications of these polarization maps are those that do not require massive simulations for accurate estimation of uncertainties, for instance estimation of cross-spectra and cross-correlations, or stacking analyses. However, the amplitude of primordial non-Gaussianity is consistent with zero within 2σ for all local, equilateral, and orthogonal configurations of the bispectrum, including for polarization E-modes. Moreover, excellent agreement is found regarding the lensing B-mode power spectrum, both internally among the various component separation codes and with the best-fit Planck 2015 Λ cold dark matter model.

266 citations

Journal ArticleDOI
TL;DR: A dynamical classical superfluid-insulator transition in a Bose-Einstein condensate trapped in an optical and a magnetic potential is predicted and an array of weakly coupled condensates driven by an external harmonic field is realized.
Abstract: We predict a dynamical classical superfluid-insulator transition in a Bose-Einstein condensate trapped in an optical and a magnetic potential. In the tight-binding limit, this system realizes an array of weakly coupled condensates driven by an external harmonic field. For small displacements of the parabolic trap about the equilibrium position, the condensates coherently oscillate in the array. For large displacements, the condensates remain localized on the side of the harmonic trap with a randomization of the relative phases. The superfluid-insulator transition is due to a discrete modulational instability, occurring when the condensate center of mass velocity is larger than a critical value.

266 citations

Journal ArticleDOI
TL;DR: In this paper, the electronic structure of iridium oxide was investigated using synchrotron-based X-ray photoemission and absorption spectroscopies with theoretical calculations.
Abstract: Iridium-based materials are among the most active and stable electrocatalysts for the oxygen evolution reaction. Amorphous iridium oxide structures are found to be more active than their crystalline counterparts. Herein, we combine synchrotron-based X-ray photoemission and absorption spectroscopies with theoretical calculations to investigate the electronic structure of Ir metal, rutile-type IrO2, and an amorphous IrOx. Theory and experiment show that while the Ir 4f line shape of Ir metal is well described by a simple Doniach–Sunjic function, the peculiar line shape of rutile-type IrO2 requires the addition of a shake-up satellite 1 eV above the main line. In the catalytically more active amorphous IrOx, we find that additional intensity appears in the Ir 4f spectrum at higher binding energy when compared with rutile-type IrO2 along with a pre-edge feature in the O K-edge. We identify these additional features as electronic defects in the anionic and cationic frameworks, namely, formally OI− and IrIII, which may explain the increased activity of amorphous IrOx electrocatalysts. We corroborate our findings by in situ X-ray diffraction as well as in situ X-ray photoemission and absorption spectroscopies. Copyright © 2015 John Wiley & Sons, Ltd.

266 citations


Authors

Showing all 3802 results

NameH-indexPapersCitations
Sabino Matarrese155775123278
G. de Zotti154718121249
J. González-Nuevo144500108318
Matt J. Jarvis144106485559
Carlo Baccigalupi137518104722
L. Toffolatti13637695529
Michele Parrinello13363794674
Marzio Nessi129104678641
Luigi Danese12839492073
Lidia Smirnova12794475865
Michele Pinamonti12684669328
David M. Alexander12565260686
Davide Maino12441088117
Dipak Munshi12436584322
Peter Onyisi11469460392
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202322
202279
2021656
2020714
2019712
2018622