605 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 Neutron Star Matter with Hyperons
Based on the Kaplan-Nelson Lagrangian, we investigate kaon condensation in
dense neutron star matter allowing for the explicit presence of hyperons. Using
various models we find that the condensate threshold is sensitive to the
behavior of the scalar density; the more rapidly it increases with baryon
density, the lower is the threshold for condensation. The presence of hyperons,
particularly the , shifts the threshold for condensation to a
higher density. In the mean field approach, with hyperons, the condensate
amplitude grows sufficiently rapidly that the nucleon effective mass vanishes
at a finite density and a satisfactory treatment of the thermodynamics cannot
be achieved. Thus, calculations of kaon-baryon interactions beyond the mean
field level appear to be necessary.Comment: 13 pages, latex, 3 figures by fax/mail from [email protected]
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
Chiral Lagrangians and Quark Condensate in Nuclei
We study the evolution with density of the quark condensate in the nuclear
medium with interacting nucleons and including the short range correlations. We
work with two chiral models, the linear sigma model and the non-linear one. For
the last one we use two versions, one which does not satisfy PCAC, and another
one which does. We show that the quark condensate, as other observables, is
independent on the variant selected. The application to physical pions excludes
the linear sigma model as a credible one. In the non-linear models our
conclusions are: first there is no systematic reaction imposed by chiral
symmetry against symmetry restoration, second, if one keeps only the s-wave
pion-nucleon interaction, the quark condensate evolves essentially linearly
with density, as if the nucleons were non interacting. The main correction
arises from the p-wave pion-nucleon interaction. Last, in the s-wave optical
potential, chiral symmetry tolerates but does not impose two body terms. On the
other hand the effect of correlations linked to the isospin symmetric amplitude
is negligible.Comment: 24 pages, LaTex, 7 PostScript Figures, a couple of misprints
corrected , 2 references added, a few modifications of the main text and
conclusion, to be published in Nucl. Phys.
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
The Inferelator: an algorithm for learning parsimonious regulatory networks from systems-biology data sets de novo
We present a method (the Inferelator) for deriving genome-wide transcriptional regulatory interactions, and apply the method to predict a large portion of the regulatory network of the archaeon Halobacterium NRC-1. The Inferelator uses regression and variable selection to identify transcriptional influences on genes based on the integration of genome annotation and expression data. The learned network successfully predicted Halobacterium's global expression under novel perturbations with predictive power similar to that seen over training data. Several specific regulatory predictions were experimentally tested and verified
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