2,788 research outputs found
p-brane superalgebras via integrability
It has long been appreciated that superalgebras with bosonic and fermionic
generators additional to those in the super-Poincare algebra underlie p-brane
and D-brane actions in superstring theory. These algebras have been revealed
via "bottom up" approaches, involving consideration of Noether charges, and by
"top down" approaches, involving the construction of manifestly supersymmetry
invariant Wess-Zumino actions. In this paper, we give an alternative derivation
of these algebras based on integrability of supersymmetry transformations
assigned to fields in order to solve a cohomology problem related to the
construction of Wess-Zumino terms for p-brane and D-brane actions.Comment: 22 pages, typo corrected, reference adde
Deriving all p-brane superalgebras via integrability
In previous work we demonstrated that the enlarged super-Poincare algebras
which underlie p-brane and D-brane actions in superstring theory can be
directly determined based on the integrability of supersymmetry transformations
assigned to fields appearing in Wess-Zumino terms. In that work we derived
p-brane superalgebras for p = 2 and 3. Here we extend our previous results and
give a compact expression for superalgebras for all valid p.Comment: 26 pages, table added, typos corrected, a few remarks added for
clarificatio
Treatment of pairing correlations in nuclei close to drip lines
We discuss the HFB equations in coordinate representation,a suitable method
for handling the full effects of the continuous quasiparticle spectrum. We show
how the continuum HFB equations can be solved with the correct asymptotic
conditions instead of the discretization conditions which are commonly used in
the literature. The continuum HFB method is illustrated with a model where the
mean field and pairing field have simple forms. The relationship with the
continuum Hartree-Fock-BCS (HF-BCS) approximation is also discussed. Realistic
HFB and HF-BCS calculations based on Skyrme interactions are compared for the
case of a neutron-rich nucleus.Comment: 12 pages, 4 Postscript figures, uses KapProc.cls, to appear in
Proceedings of NATO School " Nuclei far from stability and astrophysics",
Predeal, Romania, 200
Continuum HFB calculations with finite range pairing interactions
A new method of calculating pairing correlations in coordinate space with
finite range interactions is presented. In the Hartree-Fock-Bogoliubov (HFB)
approach the mean field part is derived from a Skyrme-type force whereas the
pairing field is constructed with a Gogny force. An iterative scheme is used
for solving the integro-differential HFB equations via the introduction of a
local equivalent potential. The method is illustrated on the case of the
nucleus C. It is shown that the results are insensitive to the cut off
value in the quasiparticle spectrum if this value is above 100 MeV.Comment: 3 figures, in press, Phys. Lett.
Evolution of the proton sd states in neutron-rich Ca isotopes
We analyze the evolution with increasing isospin asymmetry of the proton
single-particle states 2s1/2 and 1d3/2 in Ca isotopes, using non-relativistic
and relativistic mean field approaches. Both models give similar trends and it
is shown that this evolution is sensitive to the neutron shell structure, the
two states becoming more or less close depending on the neutron orbitals which
are filled. In the regions where the states get closer some parametrizations
predict an inversion between them. This inversion occurs near Ca as well
as very far from stability where the two states systematically cross each other
if the drip line predicted in the model is located far enough. We study in
detail the modification of the two single-particle energies by using the
equivalent potential in the Schroedinger-like Skyrme-Hartree-Fock equations.
The role played by central, kinetic and spin-orbit contributions is discussed.
We finally show that the effect of a tensor component in the effective
interaction considerably favors the inversion of the two proton states in
Ca.Comment: 7 figure
On mixing angles and magnetic moment of heavy tau neutrino
If the magnetic moment of unstable tau neutrinos with the mass of (MeV) is
in the region of , it is compatible with the present experimental and
cosmological bounds.
It is pointed out here, that if the tau neutrino has such a large magnetic
moment and can oscillate into a neutrino of another flavour the results from
scattering experiment at LAMPF constrain the tau neutrino mixing angles
to and
depending on the magnetic
moment value in the allowed region.Comment: 5 pages, LaTe
Quasiparticle Resonances in the BCS Approach
We present a simple method for calculating the energies and the widths of
quasiparticle resonant states. The method is based on BCS equations solved in
the Berggren representation. In this representation the quasiparticle
resonances are associated to the Gamow states of the mean field. The method is
illustrated for the case of neutron-rich nuclei O and Ni. It
is shown that the contribution of the continuum coupling to the pairing
correlations is small and largely dominated by a few resonant states close to
the continuum threshold.Comment: 14 pages, 2 figure
A consistent interpretation of recent CR nuclei and electron spectra
We try to interpret the recently updated measurement of the cosmic ray
electron (CRE) spectrum observed by Fermi-LAT, together with PAMELA data on
positron fraction, in a single-component scenario adopting different
propagation setups; we find that the model is not adequate to reproduce the two
datasets, so the evidence of an extra primary component of electrons and
positrons is strengthened. Instead, a double component scenario computed in a
Kraichnan-like diffusion setup (which is suggested by B/C and data)
gives a satisfactory fit of all exisiting measurements. We confirm that nearby
pulsars are good source candidates for the required extra-component and
we show that the predicted CRE anisotropy in our scenario is compatible with
Fermi-LAT recently published constraints.Comment: Accepted for the publication in the proceedings of the ICATPP
Conference on Cosmic Rays for Particle and Astroparticle Physics, Villa Olmo
(Como), Oct. 201
Smartphone-based photogrammetry for the 3D modeling of a geomorphological structure
The geomatic survey in the speleological field is one of the main activities that allows for the adding of both a scientific and popular value to cave exploration, and it is of fundamental importance for a detailed knowledge of the hypogean cavity. Today, the available instruments, such as laser scanners and metric cameras, allow us to quickly acquire data and obtain accurate three-dimensional models, but they are still expensive, require a careful planning phase of the survey, as well as some operator experience for their management. This work analyzes the performance of a smartphone device for a close-range photogrammetry approach for the extraction of accurate three-dimensional information of an underground cave. The image datasets that were acquired with a high-end smartphone were processed using the Structure from Motion (SfM)-based approach for dense point cloud generation: different image-matching algorithms implemented in a commercial and an open source software and in a smartphone application were tested. In order to assess the reachable accuracy of the proposed procedure, the achieved results were compared with a reference dense point cloud obtained with a professional camera or a terrestrial laser scanner. The approach has shown a good performance in terms of geometrical accuracies, computational time and applicability
- âŠ