544,855 research outputs found
A Physical Model for Co-evolution of QSOs and of their Spheroidal Hosts
At variance with most semi-analytic models, in the Anti-hierarchical Baryon
Collapse scenario (Granato et al. 2001, 2004) the main driver of the galaxy
formation and evolution is not the merging sequence but are baryon processes.
This approach emphasizes, still in the framework of the hierarchical clustering
paradigm for dark matter halos, feedback processes from supernova explosions
and from active nuclei, that tie together star formation in spheroidal galaxies
and the growth of black holes at their centers. We review some recent results
showing the remarkably successful predictive power of this scenario, which
allows us to account for the evolution with cosmic time of a broad variety of
properties of galaxies and active nuclei, which proved to be very challenging
for competing models.Comment: Invited talk at the Specola Vaticana Workshop on "AGN and Galaxy
Evolution", Castel Gandolfo, 3-6 October 2005, 10 pages, 2 figure
The cosmic dust rate across the Universe
We investigate the evolution of interstellar dust in the Universe by means of chemical evolution models of galaxies of different morphological types, reproducing the main observed features of present-day galaxies. We adopt the most updated prescriptions for dust production from supernovae and asymptotic giant branch stars as well as for dust accretion and destruction processes. Then, we study the cosmic dust rate in the framework of three different cosmological scenarios for galaxy formation: (i) a pure luminosity scenario, (ii) a number density evolution scenario, as suggested by the classical hierarchical clustering scenario and (iii) an alternative scenario, in which both spirals and ellipticals are allowed to evolve in number on an observationally motivated basis. Our results give predictions about the evolution of the dust content in different galaxies as well as the cosmic dust rate as a function of redshift. Concerning the cosmic dust rate, the best scenario is the alternative one, which predicts a peak at 2 < z < 3 and reproduces the cosmic star formation rate. We compute the evolution of the comoving dust density parameter \u3a9dust and find agreement with data for z < 0.5 in the framework of DE and alternative scenarios. Finally, the evolution of the average cosmic metallicity is presented and it shows a quite fast increase in each scenario, reaching the solar value at the present time, although most of the heavy elements are incorporated into solid grains, and therefore not observable in the gas phase
Observational constraints on Chaplygin cosmology in a braneworld scenario with induced gravity and curvature effect
We study cosmological dynamics and late-time evolution of an extended induced
gravity braneworld scenario. In this scenario, curvature effects are taken into
account via the Gauss-Bonnet term in the bulk action and there is also a
Chaplygin gas component on the brane. We show that this model mimics an
effective phantom behavior in a relatively wider range of redshifts than
previously formulated models. It also provides a natural framework for smooth
crossing of the phantom-divide line due to presence of the Chaplygin gas
component on the brane. We confront the model with observational data from type
Ia Supernovae, Cosmic Microwave Background and Baryon Acoustic Oscillations to
constraint the model parameters space.Comment: 19 pages, 11 figures, Accepted for publication in MNRA
Embedding of FRW Cosmology in DGP Scenario with a Non-Minimally Coupled Scalar Field on the Brane
We construct a DGP inspired braneworld scenario where a scalar field
non-minimally coupled to the induced Ricci curvature is present on the brane.
We show that this model allows for an embedding of the standard Friedmann
cosmology in the sense that the cosmological evolution of the background metric
on the brane can be described by the standard Friedmann equation. The relation
between our framework and the dark-energy formalism is explored.Comment: 14 pages, no figur
Behaviour of Charged Collapsing Fluids after Hydrostatic Equilibrium in R^n Gravity
The purpose of this paper is to study the transport equation and its coupling
with Maxwell equation in the framework of R^n gravity. Using
Muller-Israel-Stewart theory for the conduction of dissipative fluids, we
analyze the temperature, heat flux, viscosity and thermal conductivity in the
scenario of relaxation time. All these thermodynamical variables are appeared
in the form of a single factor whose influence is discussed on the evolution of
relativistic model for the heat conducting collapsing star.Comment: Accepted for publication in European Physical Journal
Screening Effects on Pairing in Neutron Matter
The superfluidity of neutron matter is studied in the framework of
the generalized Gorkov equation. The vertex corrections to the pairing
interaction and the self-energy corrections are introduced and approximated on
the same footing in the gap equation. A suppression of the pairing gap by more
than 50% with respect to the BCS prediction is found, which deeply changes the
scenario for the dynamical and thermal evolution of neutron stars.Comment: 5 pages, 5 figres, RevTeX4 styl
Heterogeneous aging in spin glasses
We introduce a set of theoretical ideas that form the basis for an analytical
framework capable of describing nonequilibrium dynamics in glassy systems. We
test the resulting scenario by comparing its predictions with numerical
simulations of short-range spin glasses. Local fluctuations and responses are
shown to be connected by a generalized local out-of-equilibrium
fluctuation-dissipation relation. Scaling relationships are uncovered for the
slow evolution of heterogeneities at all time scales.Comment: Substantially reorganized to improve clarity of exposition. Accepted
for publication in Physical Review Letters. 5 pages, 4 figure
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