211 research outputs found
Semi-Classical Isotropization of the Universe during a de Sitter phase
Semi-classical states for the Wheeler-DeWitt equation of a Bianchi type I
model in the presence of a scalar field are analyzed. It is outlined how this
scheme can effectively describe more general situations, where the curvature of
the Bianchi type IX model and a proper potential term for the scalar field are
present. The introduction of a cosmological constant term accounts for the
quasi-isotropization mechanism which bridges the proposed framework with a late
isotropic phase. This result makes the semi-classical Bianchi I model a
plausible scenario for the Universe pre-inflationary phase.Comment: 6 pages, accepted for publication in Phys. Rev.
Constitutional Law - Commerce Clause - Age Discrimination in Employment Act Held Applicable to States, Undermining National League of Cities v. Usery - EEOC v. Wyoming, 103 S. Ct. 1054 (1983).
New measurements of from gamma-ray bursts
Context: Data from cosmic microwave background radiation (CMB), baryon
acoustic oscillations (BAO), and supernovae Ia (SNe-Ia) support a constant dark
energy equation of state with . Measuring the evolution of
along the redshift is one of the most demanding challenges for observational
cosmology. Aims: We discuss the existence of a close relation for GRBs, named
Combo-relation, based on characteristic parameters of GRB phenomenology such as
the prompt intrinsic peak energy , the X-ray afterglow, the initial
luminosity of the shallow phase , the rest-frame duration of the
shallow phase, and the index of the late power-law decay . We use it
to measure and the evolution of the dark energy equation of state.
We also propose a new calibration method for the same relation, which reduces
the dependence on SNe Ia systematics. Methods: We have selected a sample of
GRBs with 1) a measured redshift ; 2) a determined intrinsic prompt peak
energy , and 3) a good coverage (0.3-10) keV afterglow light curves.
The fitting technique of the rest.frame (0.3-10) keV luminosity light curves
represents the core of the Combo-relation. We separate the early steep decay,
considered a part of the prompt emission, from the X-ray afterglow additional
component. Data with the largest positive residual, identified as flares, are
automatically eliminated until the p-value of the fit becomes greater than 0.3.
Results: We strongly minimize the dependency of the Combo-GRB calibration on
SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation,
which allows us to infer from GRBs alone
(1) for the CDM cosmological model, and , for the flat-Universe
variable equation of state case.Comment: 10 pages, 9 figures, 3 tables. Accepted for publication in A&A.
Truncated abstract tex
Fundamental Frequencies in the Schwarzschild Spacetime
We consider the Keplerian, radial and vertical fundamental frequencies in the
Schwarzschild spacetime to study the so-called kilohertz quasi-periodic
oscillations from low-mass X-ray binary systems. We show that, within the
Relativistic Precession Model, the interpretation of observed kilohertz
quasi-periodic oscillations in terms of the fundamental frequencies of test
particles in the Schwarzschild spacetime, allows one to infer the total mass
of the central object, the internal and external radii of
accretion disks, and innermost stable circular orbits for test
particles in a low-mass X-ray binary system. By constructing the relation
between the upper and lower frequencies and exploiting the quasi-periodic
oscillation data of the Z and Atoll sources we perform the non-linear model fit
analysis and estimate the mass of the central object. Knowing the value of the
mass we calculate the internal and external radii of
accretion disks and show that they are larger than , what was
expected.Comment: 7 pages, 6 figures, 1 tabl
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