486 research outputs found
Neutrino-pair bremsstrahlung by electrons in neutron star crusts
Neutrino-pair bremsstrahlung by relativistic degenerate electrons in a
neutron-star crust at densities (10^9 - 1.5x10^{14}) g/cm^3 is analyzed. The
processes taken into account are neutrino emission due to Coulomb scattering of
electrons by atomic nuclei in a Coulomb liquid, and electron-phonon scattering
and Bragg diffraction (the static-lattice contribution) in a Coulomb crystal.
The static-lattice contribution is calculated including the electron
band-structure effects for cubic Coulomb crystals of different types and also
for the liquid crystal phases composed of rod- and plate-like nuclei in the
neutron-star mantle (at 10^{14} - 1.5x10^{14} g/cm^3). The phonon contribution
is evaluated with proper treatment of the multi-phonon processes which removes
a jump in the neutrino bremsstrahlung emissivity at the melting point obtained
in previous works. Below 10^{13} g/cm^3, the results are rather insensitive to
the nuclear form factor, but results for the solid state near the melting point
are affected significantly by the Debye-Waller factor and multi-phonon
processes. At higher densities, the nuclear form factor becomes more
significant. A comparison of the various neutrino generation mechanisms in
neutron star crusts shows that electron bremsstrahlung is among the most
important ones.Comment: 17 pages, 13 figures, LaTeX using aa.cls and epsf.sty. A&A, in pres
Kaon Energies in Dense Matter
We discuss the role of kaon-nucleon and nucleon-nucleon correlations in kaon
condensation in dense matter. Correlations raise the threshold density for kaon
condensation, possibly to densities higher than those encountered in stable
neutron stars.Comment: RevTeX, 11 pages, 2 PostScript figures; manuscript also available, in
PostScript form, at http://www.nordita.dk/locinfo/preprints.htm
On Neutrino Emission From Dense Matter Containing Meson Condensates
We consider the rate at which energy is emitted by neutrinos from the dense
interior of neutron stars containing a Bose condensate of pions or kaons. The
rates obtained are larger, by a factor of 2, than those found earlier, and are
consistent with those found for the direct Urca processes.Comment: RevTeX, 10 page
Kaon Condensation in the Bound-State Approach to the Skyrme Model
We explore kaon condensation using the bound-state approach to the Skyrme
model on a 3-sphere. The condensation occurs when the energy required to
produce a falls below the electron fermi level. This happens at the
baryon number density on the order of 3--4 times nuclear density.Comment: LaTeX format, 15 pages. 3 Postscript figures, compressed and
uuencode
Kaon Zero-Point Fluctuations in Neutron Star Matter
We investigate the contribution of zero-point motion, arising from
fluctuations in kaon modes, to the ground state properties of neutron star
matter containing a Bose condensate of kaons. The zero-point energy is derived
via the thermodynamic partition function, by integrating out fluctuations for
an arbitrary value of the condensate field. It is shown that the vacuum
counterterms of the chiral Lagrangian ensure the cancellation of divergences
dependent on , the charge chemical potential, which may be regarded as an
external vector potential. The total grand potential, consisting of the
tree-level potential, the zero-point contribution, and the counterterm
potential, is extremized to yield a locally charge neutral, beta-equilibrated
and minimum energy ground state. In some regions of parameter space we
encounter the well-known problem of a complex effective potential. Where the
potential is real and solutions can be obtained, the contributions from
fluctuations are found to be small in comparison with tree-level contributions.Comment: 40 pages RevTeX, 3 epsf figure
State and Transition Models in Space and Time – Using STMs to Understand Broad Patterns of Ecosystem Change in Iceland
Managing ecological systems sustainably requires a deep understanding of ecosystem structure and the processes driving their dynamics. Conceptual models can lead to improved management, by providing a framework for organizing knowledge about a system and identifying the causal agents of change. We developed state-and-transition models (STMs) to describe landscape changes in Iceland over three historical periods with different human influence, from pre-settlement to present days. Our models identified the set of possible states, transitions and thresholds in these ecosystems and their changes over time. To illustrate the use of these models for predicting and improving management interventions, we applied our present-day STM to a case study in the central highlands of Iceland and monitored ecosystem changes within an ongoing field experiment with two management interventions (grazing exclusion and fertilization) in areas experiencing contrasting stages of degradation. The results of the experiment broadly align with the predictions of the model and underscore the importance of conceptual frameworks for adaptive management, where the best available knowledge is used to continuously refine and update the models
Strange Particles in Dense Matter and Kaon Condensates
We discuss the role of strangeness in dense matter and especially in neutron
stars. The early (in density) introduction of hyperons found in many
calculations is probably delayed by the decrease in vector mean field acting on
the neutron. The decrease results from both conventional many-body rescattering
effects and from the movement towards asymptotic freedom at high densities.
Subthreshold -meson production by the KaoS collaboration at GSI shows that
the -mass must be substantially lowered, by 200 MeV at . It is shown that explicit chiral symmetry breaking through the kaon
mass may be responsible for -nucleon and -nucleon scalar
attraction being weaker than obtained by simple quark scaling. The normal mode
of the strangeness minus, charge , excitation is constructed as a linear
combination of -meson and , neutron-hole state. Except for zero
momentum, where the terms are unmixed the "kaesobar" is a linear combination of
these two components.Comment: 10 pages, 8 postscript figures, Talk given at the International
Conference on Hypernuclear and Strange Particle Physics (HYP97), Brookhaven
Nat'l Lab., USA, October 13-18, 1997, to be published in Nucl. Phys.
Nonequilibrium Weak Processes in Kaon Condensation I --- Reaction rate for the thermal kaon process ---
We investigate the thermal kaon process,in which kaons are thermally produced
via nucleon-nucleon collisions.This process is relevant to nonequilibrium
dynamics of kaon condensation inside neutron stars.The reaction rates for these
processes are calculated, and their temperature and density dependences are
compared with those of other reaction rates.It is shown that the thermal kaon
process is dominant over other relevant weak reactions throughout the
nonequilibrium process, such as the kaon-induced Urca and the modified Urca
reactions, and may control the entire evolution of the kaon condensate. The
characteristic role of the soft and hard kaons during the evolution is
explained, and implications for astrophysical phenomena are briefly discussed.Comment: 31 pages,incl.10 eps figures,RevTe
First Order Kaon Condensation in Neutron Stars: Finite Size Effects in the Mixed Phase
We study the role of Coulomb and surface effects on the phase transition from
dense nuclear matter to a mixed phase of nuclear and kaon-condensed matter. We
calculate corrections to the bulk calculation of the equation of state (EOS)
and the critical density for the transition by solving explicitly for
spherical, cylindrical, and planar structures. The importance of Debye
screening in the determination of the charged particle profiles is studied in
some detail. We find that the surface and Coulomb contributions to the energy
density are small, but that they play an important role in the determination of
the critical pressure for the transition, as well as affecting the size and
geometry of favored structures. This changes the EOS over a wide range of
pressure and consequently increases the maximum mass by about 0.1 solar masses.
Implications for transport properties of the mixed phase are also discussed.Comment: 18 pages, 6 figure
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