11 research outputs found
Joint constraints on the lepton asymmetry of the Universe and neutrino mass from the Wilkinson Microwave Anisotropy Probe
We use the Wilkinson Microwave Anisotropy Probe (WMAP) data on the spectrum
of cosmic microwave background anisotropies to put constraints on the present
amount of lepton asymmetry L, parameterized by the dimensionless chemical
potential (also called degeneracy parameter) xi and on the effective number of
relativistic particle species. We assume a flat cosmological model with three
thermally distributed neutrino species having all the same mass and chemical
potential, plus an additional amount of effectively massless exotic particle
species. The extra energy density associated to these species is parameterized
through an effective number of additional species DeltaN_oth$. We find that
0<|xi|<1.1 and correspondingly 0<|L|<0.9 at 2sigma, so that WMAP data alone
cannot firmly rule out scenarios with a large lepton number; moreover, a small
preference for this kind of scenarios is actually found. We also discuss the
effect of the asymmetry on the estimation of other parameters and in particular
of the neutrino mass. In the case of perfect lepton symmetry, we obtain the
standard results. When the amount of asymmetry is left free, we find \sum m_nu
< 3.6 eV at 2sigma. Finally we study how the determination of |L| is affected
by the assumptions on DeltaN_oth. We find that lower values of the extra energy
density allow for larger values of the lepton asymmetry, effectively ruling
out, at 2sigma level, lepton symmetric models with DeltaN_oth=0.Comment: 11 pages, 2 figures. Uses RevTex4. Minor changes made to match
published versio
What can we learn from GRBs?
We review our recent results on the classification of long and short gamma-ray bursts (GRBs) in different subclasses. We provide observational evidences for the binary nature of GRB progenitors. For long bursts the induced gravitational collapse (IGC) paradigm proposes as progenitor a tight binary system composed of a carbon-oxygen core (COcore) and a neutron star (NS) companion; the supernova (SN) explosion of the COcore triggers a hypercritical accretion process onto the companion NS. For short bursts a NS–NS merger is traditionally adopted as the progenitor. We also indicate additional sub-classes originating from different progenitors: (COcore)–black hole (BH), BH–NS, and white dwarf–NS binaries. We also show how the outcomes of the further evolution of some of these sub-classes may become the progenitor systems of other sub-classes
The canonical Gamma-Ray Bursts and their "precursors"
The fireshell model for Gamma-Ray Bursts (GRBs) naturally leads to a
canonical GRB composed of a proper-GRB (P-GRB) and an afterglow. P-GRBs,
introduced by us in 2001, are sometimes considered "precursors" of the main GRB
event in the current literature. We show in this paper how the fireshell model
leads to the understanding of the structure of GRBs, with precise estimates of
the time sequence and intensities of the P-GRB and the of the afterglow. It
leads as well to a natural classification of the canonical GRBs which overcomes
the traditional one in short and long GRBs.Comment: 4 pages, 3 figures, Proceedings of the 2008 Nanjing GRB conferenc
Relativistic kinetic theory: with applications in astrophysics and cosmology
Relativistic kinetic theory has widespread application in astrophysics and cosmology. The interest has grown in recent years as experimentalists are now able to make reliable measurements on physical systems where relativistic effects are no longer negligible. This ambitious monograph is divided into three parts. It presents the basic ideas and concepts of this theory, equations and methods, including derivation of kinetic equations from the relativistic BBGKY hierarchy and discussion of the relation between kinetic and hydrodynamic levels of description. The second part introduces elements of computational physics with special emphasis on numerical integration of Boltzmann equations and related approaches, as well as multi-component hydrodynamics. The third part presents an overview of applications ranging from covariant theory of plasma response, thermalization of relativistic plasma, comptonization in static and moving media to kinetics of self-gravitating systems, cosmological structure formation and neutrino emission during the gravitational collapse
What can we learn from GRBs?
We review our recent results on the classification of long and short gamma-ray bursts (GRBs) in different subclasses. We provide observational evidences for the binary nature of GRB progenitors. For long bursts the induced gravitational collapse (IGC) paradigm proposes as progenitor a tight binary system composed of a carbon-oxygen core (COcore) and a neutron star (NS) companion; the supernova (SN) explosion of the COcore triggers a hypercritical accretion process onto the companion NS. For short bursts a NS–NS merger is traditionally adopted as the progenitor. We also indicate additional sub-classes originating from different progenitors: (COcore)–black hole (BH), BH–NS, and white dwarf–NS binaries. We also show how the outcomes of the further evolution of some of these sub-classes may become the progenitor systems of other sub-classes