Search results for "Cosmologia"
showing 10 items of 73 documents
Unduland universe: expansion with alternating eras of acceleration and deceleration
2005
If the equation of state for 'dark energy' varies periodically, the expansion of the Universe may have undergone alternating eras of acceleration and deceleration. We examine a specific form that survives existing observational tests, does not single out the present state of the Universe as exceptional, and suggests a future much like the matter-dominated past: a smooth expansion without a final inflationary epoch.
Intrinsic energy of Lema\^itre-Tolman-Bondi models and cosmological implications
2013
Recently, some Lema{\^{\i}}tre-Tolman-Bondi metrics have been considered as models alternative to the dark energy within the Friedmann-Lema{\^{\i}}tre-Robertson-Walker universes. The vanishing of the intrinsic energy of these metrics is examined since such a vanishing, in the present case and in general, could be interpreted as a necessary condition to consider the possibility of the quantum creation of a metric. More specifically, this vanishing is examined in the particular case where the Lema{\^{\i}}tre-Tolman-Bondi metrics behave asymptotically like a Friedmann-Lema{\^{\i}}tre-Robertson-Walker universe. Finally, we deal with a particular model ruled out after being confronted with cosmi…
Diagnostic Potential of Cosmic-Neutrino Absorption Spectroscopy
2004
Annihilation of extremely energetic cosmic neutrinos on the relic-neutrino background can give rise to absorption lines at energies corresponding to formation of the electroweak gauge boson $Z^{0}$. The positions of the absorption dips are set by the masses of the relic neutrinos. Suitably intense sources of extremely energetic ($10^{21}$ -- $10^{25}$-eV) cosmic neutrinos might therefore enable the determination of the absolute neutrino masses and the flavor composition of the mass eigenstates. Several factors--other than neutrino mass and composition--distort the absorption lines, however. We analyze the influence of the time-evolution of the relic-neutrino density and the consequences of …
Evolution of polarization orientations in a flat universe with vector perturbations: CMB and quasistellar objects
2007
Various effects produced by vector perturbations (vortical peculiar velocity fields) of a flat Friedmann-Robertson-Walker background are considered. In the presence of this type of perturbations, the polarization vector rotates. A formula giving the rotation angle is obtained and, then, it is used to prove that this angle depends on both the observation direction and the emission redshift. Hence, rotations are different for distinct quasars and also for the Cosmic Microwave Background (CMB) radiation coming along different directions (from distinct points of the last scattering surface). As a result of these rotations, some correlations could appear in an initially random field of quasar po…
Cosmological radiation density with non-standard neutrino-electron interactions
2021
Neutrino non-standard interactions (NSI) with electrons are known to alter the picture of neutrino decoupling from the cosmic plasma. NSI modify both flavour oscillations through matter effects, and the annihilation and scattering between neutrinos and electrons and positrons in the thermal plasma. In view of the forthcoming cosmological observations, we perform a precision study of the impact of non-universal and flavour-changing NSI on the effective number of neutrinos, $N_{eff}$. We present the variation of $N_{eff}$ arising from the different NSI parameters and discuss the existing degeneracies among them, from cosmology alone and in relation to the current bounds from terrestrial exper…
New constraints on coupled dark energy from the Planck satellite experiment
2013
We present new constraints on coupled dark energy from the recent measurements of the cosmic microwave background anisotropies from the Planck satellite mission. We found that a coupled dark energy model is fully compatible with the Planck measurements, deriving a weak bound on the dark matter-dark energy coupling parameter xi = -0.49(-0.31)(+0.19) at 68% C.L. Moreover if Planck data are fitted to a coupled dark energy scenario, the constraint on the Hubble constant is relaxed to H-0 = 72.1(-2.3)(+3.2) km/s/Mpc, solving the tension with the Hubble Space Telescope (HST) value. We show that a combined PLANCK + HST analysis provides significant evidence for coupled dark energy finding a nonzer…
A non-resonant dark-side solution to the solar neutrino problem
2001
We re-analyse spin-flavour precession solutions to the solar neutrino problem in the light of the recent SNO CC result as well as the 1258--day Super-Kamiokande data and the upper limit on solar anti-neutrinos. In a self-consistent magneto-hydrodynamics approach the resulting scheme has only 3 effective parameters: $\Delta m^2$, $\mu B_\perp$ and the neutrino mixing angle $\theta$. We show how a rates-only analysis for fixed $\mu B_\perp$ slightly favours spin-flavour precession (SFP) solutions over oscillations (OSC). In addition to the resonant solution (RSFP for short), there is a new non-resonant solution (NRSFP) in the ``dark-side''. Both RSFP and NRSFP lead to flat recoil energy spect…
Inflation, quantum fields, and CMB anisotropies
2009
Revert field Inflationary cosmology has proved to be the most successful at predicting the properties of the anisotropies observed in the cosmic microwave background (CMB). In this essay we show that quantum field renormalization significantly influences the generation of primordial perturbations and hence the expected measurable imprint of cosmological inflation on the CMB. However, the new predictions remain in agreement with observation, and in fact favor the simplest forms of inflation. In the near future, observations of the influence of gravitational waves from the early universe on the CMB will test our new predictions.
Commissioning of the ATLAS Muon Spectrometer with cosmic rays
2010
The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector i…
Concezioni dei luoghi e figure dell’alterità: il mare tra i Wayuu. Parte prima
2010
Prima parte di un articolo in cui si propone un’analisi della cosmologia dei Wayuu,una popolazione indigena sudamericana, dalla prospettiva delle valenze simboliche che vi assume il mare, luogo di provenienza o residenza dell’Altro da sé, identificato sia con figure di spiriti, sia con i colonizzatori di origine europea, sia con gli animali da loro introdotti. Dopo aver presentato alcune posizioni del dibattito antropologico contemporaneo sui rapporti tra concezioni dell’alterità e senso dei luoghi, si esamina la relazione complessa tra i valori simbolici e sociali della pesca e quelli della pastorizia (attività introdotta dopo l’arrivo dei primi Europei), e la connessione tra il mare e una…