459 research outputs found
Continuum and Symmetry-Conserving Effects in Drip-line Nuclei Using Finite-range Forces
We report the first calculations of nuclear properties near the drip-lines
using the spherical Hartree-Fock-Bogoliubov mean-field theory with a
finite-range force supplemented by continuum and particle number projection
effects. Calculations were carried out in a basis made of the eigenstates of a
Woods-Saxon potential computed in a box, thereby garanteeing that continuum
effects were properly taken into account. Projection of the self-consistent
solutions on good particle number was carried out after variation, and an
approximation of the variation after projection result was used. We give the
position of the drip-lines and examine neutron densities in neutron-rich
nuclei. We discuss the sensitivity of nuclear observables upon continuum and
particle-number restoration effects.Comment: 5 pages, 3 figures, Phys. Rev. C77, 011301(R) (2008
Nuclear Halos and Drip Lines in Symmetry-Conserving Continuum HFB Theory
We review the properties of nuclear halos and nuclear skins in drip line
nuclei in the framework of the spherical Hartree-Fock-Bogoliubov theory with
continuum effects and projection on good particle number with the Gogny force.
We first establish the position of the un-projected HFB drip lines for the two
most employed parametrizations of the Gogny force and show that the use of
finite-range interactions leads almost always to small-sized halos, even in the
least bound nuclei, which is in agreement with most mean-field predictions. We
also discuss the size of the neutron skin at the drip line and its relation to
neutron asymmetry. The impact of particle-number projection and its conceptual
consequences near the drip line are analyzed in detail. In particular, we
discuss the role of the chemical potential in a projected theory and the
criteria required to define the drip line. We show that including particle
number projection can shift the latter, in particular near closed shells. We
notice that, as a result, the size of the halo can be increased due to larger
pairing correlations. However, combining the most realistic pairing
interaction, a proper treatment of the continuum and particle number projection
does not permit to reproduce the very large halos observed in very light
nuclei.Comment: Re-submitted to Phys. Rev. C after Referee's review. Layout of
figures changed to cope with editor's requirement
Probing Cold Dark Matter Cusps by Gravitational Lensing
I elaborate on my prediction that an indirect detection of cold dark matter
(CDM) may be possible by observing the gravitational lensing effects of the CDM
cusp caustics at cosmological distances. Cusps in the distribution of CDM are
plentiful once density perturbations enter the nonlinear regime of structure
formation. Caustic ring model of galactic halo formation provides a well
defined density profile and geometry near the cusps of the caustic rings. I
calculate the gravitational lensing effects of the cusps in this model. As a
pointlike background source passes behind a cusp of a cosmological foreground
halo, the magnification in its image may be detected by present instruments.
Depending on the strength of detected effect and the time scale of brightness
change, it may even be possible to discriminate between the CDM candidates:
axions and weakly interacting massive particles.Comment: Invited Contribution to the IJMPD Special Issue on Dark Matter and
Dark Energy edited by D. Ahluwalia-Khalilova and D. Grumiller. To appear in
Int. J. Mod. Phys. D Special December 2006 issu
Vacuum Fluctuations of Energy Density can lead to the observed Cosmological Constant
The energy density associated with Planck length is while the energy density associated with the Hubble length is
where . The observed value of the dark
energy density is quite different from {\it either} of these and is close to
the geometric mean of the two: .
It is argued that classical gravity is actually a probe of the vacuum {\it
fluctuations} of energy density, rather than the energy density itself. While
the globally defined ground state, being an eigenstate of Hamiltonian, will not
have any fluctuations, the ground state energy in the finite region of space
bounded by the cosmic horizon will exhibit fluctuations . When used as a source of gravity, this should
lead to a spacetime with a horizon size . This bootstrapping condition
leads naturally to an effective dark energy density which is precisely the observed value. The model
requires, either (i) a stochastic fluctuations of vacuum energy which is
correlated over about a Hubble time or (ii) a semi- anthropic interpretation.
The implications are discussed.Comment: r pages; revtex; comments welcom
Origin of Correlations between Central Black Holes Masses and Galactic Bulge Velocity Dispersions
We argue that the observed correlations between central black holes masses
M_{BH} and galactic bulge velocity dispersions \sigma_e in the form
M_{BH}\propto\sigma_e^4 may witness on the pregalactic origin of massive black
holes. Primordial black holes would be the centers for growing protogalaxies
which experienced multiple mergers with ordinary galaxies. This process is
accompanied by the merging of black holes in the galactic nuclei.Comment: 6 pages, 1 figure, submitted to Astron. and Astrophys. Transaction
The anapole moments in disk-form MS-wave ferrite particle
The anapole moments describe the parity-violating parity-odd,
time-reversal-even couplings between elementary particles and the
electromagnetic (EM) field. Surprisingly, the anapole-like moment properties
can be found in certain artificially engineered physical systems. In
microwaves, ferrite resonators with multi-resonance magnetostatic-wave
(MS-wave) oscillations may have sizes two-four orders less than the free-space
EM wavelength at the same frequency. MS-wave oscillations in a ferrite sample
occupy a special place between the pure electromagnetic and spin-wave
(exchange) processes. The energy density of MS-wave oscillations is not the
electromagnetic-wave density of energy and not the exchange energy density as
well. These microscopic oscillating objects -- the particles -- may interact
with the external EM fields by a very specific way, forbidden for the classical
description. To describe such interactions, the quantum mechanical analysis
should be used. The presence of surface magnetic currents is one of the
features of MS oscillations in a normally magnetized ferrite disk resonator.
Because of such magnetic currents, MS oscillations in ferrite disk resonators
become parity violating. The parity-violating couplings between disk-form
ferrite particles and the external EM field should be analyzed based on the
notion of an anapole moment.Comment: 20 pages, 2 figures, PDF (created from MS-Word
Role of low- component in deformed wave functions near the continuum threshold
The structure of deformed single-particle wave functions in the vicinity of
zero energy limit is studied using a schematic model with a quadrupole deformed
finite square-well potential. For this purpose, we expand the single-particle
wave functions in multipoles and seek for the bound state and the Gamow
resonance solutions. We find that, for the states, where is
the -component of the orbital angular momentum, the probability of each
multipole components in the deformed wave function is connected between the
negative energy and the positive energy regions asymptotically, although it has
a discontinuity around the threshold. This implies that the
resonant level exists physically unless the component is inherently large
when extrapolated to the well bound region. The dependence of the multipole
components on deformation is also discussed
Axiverse and Black Hole
String theory/M-theory generally predicts that axionic fields with a broad
mass spectrum extending below 10^{-10}eV are produced after compactification to
four dimensions. These axions/fields provoke a rich variety of cosmophysical
phenomena on different scales depending on their masses and provide us new
windows to probe the ultimate theory. In this article, after overviewing this
axiverse idea, I take up the black hole instability as the most fascinating one
among such axionic phenomena and explain its physical mechanism and
astrophysical predictions.Comment: References added; 32 pages, 24 figures. Based on the lecture at the
2011 Shanghai Asia-Pacific School and Workshop on Gravitatio
A numerical investigation of the stability of steady states and critical phenomena for the spherically symmetric Einstein-Vlasov system
The stability features of steady states of the spherically symmetric
Einstein-Vlasov system are investigated numerically. We find support for the
conjecture by Zeldovich and Novikov that the binding energy maximum along a
steady state sequence signals the onset of instability, a conjecture which we
extend to and confirm for non-isotropic states. The sign of the binding energy
of a solution turns out to be relevant for its time evolution in general. We
relate the stability properties to the question of universality in critical
collapse and find that for Vlasov matter universality does not seem to hold.Comment: 29 pages, 10 figure
Gravity from Spinors
We investigate a possible unified theory of all interactions which is based
only on fundamental spinor fields. The vielbein and metric arise as composite
objects. The effective quantum gravitational theory can lead to a modification
of Einstein's equations due to the lack of local Lorentz-symmetry. We explore
the generalized gravity with global instead of local Lorentz symmetry in first
order of a systematic derivative expansion. At this level diffeomorphisms and
global Lorentz symmetry allow for two new invariants in the gravitational
effective action. The one which arises in the one loop approximation to spinor
gravity is consistent with all present tests of general relativity and
cosmology. This shows that local Lorentz symmetry is tested only very partially
by present observations. In contrast, the second possible new coupling is
severely restricted by present solar system observations.Comment: New material on absence of observational tests of local Lorentz
invariance, 21 pages, to appear in Phys.Rev.
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