11 research outputs found
Testing theories that predict time variation of fundamental constants
We consider astronomical and local bounds on time variation of fundamental
constants to test some generic Kaluza-Klein-like models and some particular
cases of Beckenstein theory. Bounds on the free parameters of the different
theories are obtained. Furthermore, we find that none of the proposed models,
is able to explain recent results [Webb99,Webb00] claiming an observed
variation of the fine structure constant from quasar absorption systems at
redshifts .Comment: 18 pages, 2 figures, new data adde
The decompression of the outer neutron star crust and r-process nucleosynthesis
The rapid neutron-capture process, or r-process, is known to be fundamental
for explaining the origin of approximately half of the A>60 stable nuclei
observed in nature. In recent years nuclear astrophysicists have developed more
and more sophisticated r-process models, by adding new astrophysical or nuclear
physics ingredients to explain the solar system composition in a satisfactory
way. Despite these efforts, the astrophysical site of the r-process remains
unidentified. The composition of the neutron star outer crust material is
investigated after the decompression that follows its possible ejection. The
composition of the outer crust of a neutron star is estimated before and after
decompression. Two different possible initial conditions are considered, namely
an idealized crust composed of cold catalyzed matter and a crust initially in
nuclear statistical equilibrium at temperatures around 10 GK. We show that in
this second case before decompression and at temperatures typically
corresponding to 8 GK, the Coulomb effect due to the high densities in the
crust leads to an overall composition of the outer crust in neutron-rich nuclei
with a mass distribution close to the solar system r-abundance distribution.
Such distributions differ, however, from the solar one due to a systematic
shift in the second peak to lower values. After decompression, the capture of
the few neutrons per seed nucleus available in the hot outer crust leads to a
final distribution of stable neutron-rich nuclei with a mass distribution of 80
< A < 140 nuclei in excellent agreement with the solar distribution, provided
the outer crust is initially at temperatures around 8 GK and all layers of the
outer crust are ejected. The decompression of the neutron star matter from the
outer crust provides suitable conditions for a robust r-processing of the light
species, i.e., r-nuclei with A < 140.Comment: 11 pages, 16 figures; Accepted in A&A main Journa
Charge conservation and time-varying speed of light
It has been recently claimed that cosmologies with time dependent speed of
light might solve some of the problems of the standard cosmological scenario,
as well as inflationary scenarios. In this letter we show that most of these
models, when analyzed in a consistent way, lead to large violations of charge
conservation. Thus, they are severly constrained by experiment, including those
where is a power of the scale factor and those whose source term is the
trace of the energy-momentum tensor. In addition, early Universe scenarios with
a sudden change of related to baryogenesis are discarded.Comment: 4 page
A large stellar evolution database for population synthesis studies. V. Stellar models and isochrones with CNONa abundance anticorrelations
We present a new grid of stellar models and isochrones for old stellar
populations, covering a large range of [Fe/H] values, for an heavy element
mixture characterized by CNONa abundance anticorrelations as observed in
Galactic globular cluster stars. The effect of this metal abundance pattern on
the evolutionary properties of low mass stars, from the main sequence to the
horizontal branch phase is analyzed. We perform comparisons between these new
models, and our reference alpha-enhanced calculations, and discuss briefly
implications for CMDs showing multiple main sequence or subgiant branches. A
brief qualitative discussion of the effect of CN abundances on color-T_{eff}
transformations is also presented, highlighting the need to determine
theoretical color transformations for the appropriate metal mixture, if one
wants to interpret observations in the Stroemgren system, or broadband filters
blueward of the Johnson V-band.Comment: 25 pages, 7 figures, ApJ in pres
Event Texture Search for Phase Transitions in Pb+Pb Collisions
NA44 uses a 512 channel Si pad array covering to study charged hadron production in 158 A GeV Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a Discrete Wavelet Transformation, to probe the texture of particle distributions event-by-event, allowing simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we search for signals of clustering and of critical behavior in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy ion event generators, and with a reference sample created via event mixing. An upper limit is set on the probability and magnitude of dynamical fluctuations