27,833 research outputs found
B\"acklund transformations in 2D dilaton gravity
We give a B\"acklund transformation connecting a generic 2D dilaton gravity
theory to a generally covariant free field theory. This transformation provides
an explicit canonical transformation relating both theories.Comment: LaTeX file, 7 page
The Dirac particle on central backgrounds and the anti-de Sitter oscillator
It is shown that, for spherically symmetric static backgrounds, a simple
reduced Dirac equation can be obtained by using the Cartesian tetrad gauge in
Cartesian holonomic coordinates. This equation is manifestly covariant under
rotations so that the spherical coordinates can be separated in terms of
angular spinors like in special relativity, obtaining a pair of radial
equations and a specific form of the radial scalar product. As an example, we
analytically solve the anti-de Sitter oscillator giving the formula of the
energy levels and the form of the corresponding eigenspinors.Comment: 16 pages, Late
Extended Skyrme Equation of State in asymmetric nuclear matter
We present a new equation of state for infinite systems (symmetric,
asymmetric and neutron matter) based on an extended Skyrme functional
constrained by microscopic Brueckner-Bethe-Goldstone results. The resulting
equation of state reproduces with very good accuracy the main features of
microscopic calculations and it is compatible with recent measurements of two
times Solar-mass neutron stars. We provide all necessary analytical expressions
to facilitate a quick numerical implementation of quantities of astrophysical
interest
Spurious finite-size instabilities in nuclear energy density functionals: spin channel
It has been recently shown, that some Skyrme functionals can lead to
non-converging results in the calculation of some properties of atomic nuclei.
A previous study has pointed out a possible link between these convergence
problems and the appearance of finite-size instabilities in symmetric nuclear
matter (SNM) around saturation density.
We show that the finite-size instabilities not only affect the ground state
properties of atomic nuclei, but they can also influence the calculations of
vibrational excited states in finite nuclei. We perform systematic fully-self
consistent Random Phase Approximation (RPA) calculations in spherical
doubly-magic nuclei. We employ several Skyrme functionals and vary the
isoscalar and isovector coupling constants of the time-odd term
. We determine critical values of these
coupling constants beyond which the RPA calculations do not converge because
RPA the stability matrix becomes non-positive.By comparing the RPA calculations
of atomic nuclei with those performed for SNM we establish a correspondence
between the critical densities in the infinite system and the critical coupling
constants for which the RPA calculations do not converge. We find a
quantitative stability criterion to detect finite-size instabilities related to
the spin term of a functional. This
criterion could be easily implemented into the standard fitting protocols to
fix the coupling constants of the Skyrme functional
Gas-Rich Companions of Isolated Galaxies
We have used the VLA to search for gaseous remnants of the galaxy formation
process around six extremely isolated galaxies. We found two distinct HI clouds
around each of two galaxies in our sample (UGC 9762 & UGC 11124). These clouds
are rotating and appear to have optical counterparts, strongly implying that
they are typical dwarf galaxies. The companions are currently weakly
interacting with the primary galaxy, but have short dynamical friction
timescales (~1 Gyr) suggesting that these triple galaxy systems will shortly
collapse into one massive galaxy. Given that the companions are consistent with
being in circular rotation about the primary galaxy, and that they have small
relative masses, the resulting merger will be a minor one. The companions do,
however, contain enough gas that the merger will represent a significant
infusion of fuel to drive future star formation, bar formation, or central
activity, while building up the mass of the disk thus making these systems
important pieces of the galaxy formation and evolution process.Comment: Corrected dynamical friction calculation error. Revised discussion &
conclusions. 7 pages, 4 tables, 6 figures, to appear in May 1999 Astronomical
Journa
Satellite Galaxies and Fossil Groups in the Millennium Simulation
We use a semianalytic galaxy catalogue constructed from the Millennium
Simulation to study the satellites of isolated galaxies in the LCDM cosmogony.
This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites)
allows the characterization, with minimal statistical uncertainty, of the
dynamical properties of satellite/primary galaxy systems in a LCDM universe. We
find that, overall, the satellite population traces the dark matter rather
well: its spatial distribution and kinematics may be approximated by an NFW
profile with a mildly anisotropic velocity distribution. Their spatial
distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg''
effect that reflects the misalignment between the major axis and angular
momentum of the host halo. The isolation criteria for our primaries picks not
only galaxies in sparse environments, but also a number of primaries at the
centre of ''fossil'' groups. We find that the abundance and luminosity function
of these unusual systems are in reasonable agreement with the few available
observational constraints. We recover the expected L_{host} \sigma_{sat}^3
relation for LCDM models for truly-isolated primaries. Less strict primary
selection, however, leads to substantial modification of the scaling relation.
Our analysis also highlights a number of difficulties afflicting studies that
rely on blind stacking of satellite systems to constrain the mean halo mass of
the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
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