13,939 research outputs found
Self-consistent description of multipole strength: systematic calculations
We use the quasiparticle random phase approximation with a few Skyrme density
functionals to calculate strength functions in the Jpi = 0+, 1-, and 2+
channels for even Ca, Ni, and Sn isotopes, from the proton drip line to the
neutron drip line. We show where and how low-lying strength begins to appear as
N increases. We also exhibit partial energy-weighted sums of the transition
strength as functions of N for all nuclei calculated, and transition densities
for many of the interesting peaks. We find that low-energy strength increases
with N in all multipoles, but with distinctive features in each. The low-lying
0+ strength near the neutron at large N barely involves protons at all, with
the strength coming primarily from a single two-quasineutron configuration with
very large spatial extent. The low-lying 1- strength is different, with protons
contributing to the transition density in the nuclear interior together with
neutrons at large radii. The low-lying 2+ transition strength goes largely to
more localized states. The three Skyrme interactions we test produce similar
results, differing most significantly in their predictions for the location of
the neutron drip line, the boundaries of deformed regions, energies of and
transition strengths to the lowest 2+ states between closed shells, and
isovector energy-weighted sum rules.Comment: 43 pages, 48 figures, 1 tabl
Quantum oscillations observed in graphene at microwave frequencies
We have measured the microwave conductance of mechanically exfoliated
graphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits
quantum oscillations, and is independent of the frequency
Chiral two-body currents and neutrinoless double-β decay in the quasiparticle random-phase approximation
We test the effects of an approximate treatment of two-body contributions to the axial-vector current on the quasiparticle random-phase approximation (QRPA) matrix elements for neutrinoless double-beta decay in a range of isotopes. The form and strength of the two-body terms come from chiral effective-field theory. The two-body currents typically reduce the matrix elements by about 20%, not as much as in shell-model calculations. One reason for the difference is that standard practice in the QRPA is to adjust the strength of the isoscalar pairing interaction to reproduce two-neutrino double-beta decay lifetimes. Another may be the larger QRPA single-particle space. Whatever the reasons, the effects on neutrinoless decay are significantly less than those on two-neutrino decay, both in the shell model and the QRPA
Mesoscopic Spin-Hall Effect in 2D electron systems with smooth boundaries
Spin-Hall effect in ballistic 2D electron gas with Rashba-type spin-orbit
coupling and smooth edge confinement is studied. We predict that the interplay
of semiclassical electron motion and quantum dynamics of spins leads to several
distinct features in spin density along the edge that originate from
accumulation of turning points from many classical trajectories. Strong peak is
found near a point of the vanishing of electron Fermi velocity in the lower
spin-split subband. It is followed by a strip of negative spin density that
extends until the crossing of the local Fermi energy with the degeneracy point
where the two spin subbands intersect. Beyond this crossing there is a wide
region of a smooth positive spin density. The total amount of spin accumulated
in each of these features exceeds greatly the net spin across the entire edge.
The features become more pronounced for shallower boundary potentials,
controlled by gating in typical experimental setups.Comment: 4 pages, 4 figures, published versio
Theory of Spin Hall conductivity in n-doped GaAs
We develop a theory of extrinsic spin currents in semiconductors, resulting
from spin-orbit coupling at charged scatterers, which leads to skew scattering
and side jump contributions to the spin Hall conductance. Applying the theory
to bulk n-GaAs, without any free parameters, we find spin currents that are in
reasonable agreement with recent experiments by Kato et al. [Science 306, 1910
(2004)].Comment: 5 pages, 1 figur
The discrete fragmentation equations : semigroups, compactness and asynchronous exponential growth
In this paper we present a class of fragmentation semigroups which are compact in a scale of spaces defined in terms of finite higher moments. We use this compactness result to analyse the long time behaviour of such semigroups and, in particular, to prove that they have the asynchronous growth property. We note that, despite compactness, this growth property is not automatic as the fragmentation semigroups are not irreducible
Direct detection of supersymmetric dark matter- Theoretical rates for transitions to excited states
The recent WMAP data have confirmed that exotic dark matter together with the
vacuum energy (cosmological constant) dominate in the flat Universe.
Supersymmetry provides a natural dark matter candidate, the lightest
supersymmetric particle (LSP). Thus the direct dark matter detection is central
to particle physics and cosmology. Most of the research on this issue has
hitherto focused on the detection of the recoiling nucleus. In this paper we
study transitions to the excited states, focusing on the first excited state at
50 keV of Iodine A=127. We find that the transition rate to this excited state
is about 10 percent of the transition to the ground state. So, in principle,
the extra signature of the gammai ray following its de-excitation can be
exploited experimentally.Comment: LaTex, 13 pages, 3 postscript figures, 1 table, to appear in IJMP
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