2,304 research outputs found
Building scars for integrable systems
It is shown, by means of a simple specific example, that for integrable
systems it is possible to build up approximate eigenfunctions, called {\it
asymptotic eigenfunctions}, which are concentrated as much as one wants to a
classical trajectory and have a lifetime as long as one wants. These states are
directly related to the presence of shell structures in the quantal spectrum of
the system. It is argued that the result can be extended to classically chaotic
system, at least in the asymptotic regime
The maximum and minimum mass of protoneutron stars in the Brueckner theory
We study the structure of protoneutron stars within the finite-temperature
Brueckner-Bethe-Goldstone theoretical approach, paying particular attention to
how it is joined to a low-density nuclear equation of state (EOS). We find a
slight sensitivity of the minimum value of the protoneutron star mass on the
low-density equation of state, whereas the maximum mass is hardly affected.Comment: 8 pages, 8 figure
Hybrid protoneutron stars with the MIT bag model
We study the hadron-quark phase transition in the interior of protoneutron
stars. For the hadronic sector, we use a microscopic equation of state
involving nucleons and hyperons derived within the finite-temperature
Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and
three-body forces. For the description of quark matter, we employ the MIT bag
model both with a constant and a density-dependent bag parameter. We calculate
the structure of protostars with the equation of state comprising both phases
and find maximum masses below 1.6 solar masses. Metastable heavy hybrid
protostars are not found.Comment: 12 pages, 9 figures submitted to Phys. Rev.
Strange hadronic stellar matter within the Brueckner-Bethe-Goldstone theory
In the framework of the non-relativistic Brueckner-Bethe-Goldstone theory, we
derive a microscopic equation of state for asymmetric and -stable matter
containing and hyperons. We mainly study the effects of
three-body forces (TBFs) among nucleons on the hyperon formation and the
equation of state (EoS). We find that, when TBFs are included, the stellar core
is almost equally populated by nucleons and hyperons. The resulting EoS, which
turns out to be extremely soft, has been used in order to calculate the static
structure of neutron stars. We obtain a value of the maximum mass of 1.26 solar
masses (1 solar mass ). Stellar rotations
increase this value by about 12%.Comment: 4 pages, Latex, 2 figures included. To appear in the Proceedings of
'' Bologna 2000 - Structure of the Nucleus at the Dawn of the Century'', May
29- June 3, 2000, Bologna, Ital
Protoneutron stars within the Brueckner-Bethe-Goldstone theory
We study the structure of newly born neutron stars (protoneutron stars)
within the finite temperature Brueckner-Bethe-Goldstone theoretical approach
including also hyperons. We find that for purely nucleonic stars both finite
temperature and neutrino trapping reduce the value of the maximum mass. For
hyperonic stars the effect is reversed, because neutrino trapping shifts the
appearance of hyperons to larger baryon density and stiffens considerably the
equation of state.Comment: 11 pages, 7 figures, submitted to Astronomy & Astrophysic
Neutron stars and the transition to color-superconducting quark matter
We explore the relevance of color superconductivity inside a possible quark
matter core for the bulk properties of neutron stars. For the quark phase we
use an Nambu--Jona-Lasinio (NJL) type model, extended to include diquark
condensates. For the hadronic phase, a microscopic many-body model is adopted,
with and without strangeness content. In our calculations, a sharp boundary is
assumed between the hadronic and the quark phases. For NJL model parameters
fitted to vacuum properties we find that no star with a pure quark core does
exist. Nevertheless the presence of color superconducting phases can lower the
neutron star maximum mass substantially. In some cases, the transition to quark
matter occurs only if color superconductivity is present. Once the quark phase
is introduced, the value of the maximum mass stays in any case below the value
of two solar masses.Comment: 11 pages, 3 figures, v2: minor corrections in the text, layout of the
figures improved, references added, v3: transition densities from hadronic to
quark matter added, version accepted for publication in PL
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