168 research outputs found
Theoretical mean field and experimental occupation probabilities in the double beta decay system 76Ge to 76Se
Usual Woods-Saxon single particle levels with BCS pairing are not able to
reproduce the experimental occupation probabilities of the proton and neutron
levels 1p_{3/2}, 1p_{1/2}, 0f_{5/2}, 0g_{9/2} in the double-beta decay system
76Ge to 76Se. Shifting down the 0g_{9/2} level by hand can explain the data but
it is not satisfactory. Here it is shown that a selfconsistent Hartree-Fock+BCS
approach with experimental deformations for 76Ge and 76Se may decisively
improve the agreement with the recent data on occupation probabilities by
Schiffer et al. and Kay et al. Best agreement with available data on 76Ge and
76Se, as well as on neighbor isotopes, is obtained when the spin-orbit strength
for neutrons is allowed to be larger than that for protons. The two-neutrino
double-beta decay matrix element is also shown to agree with data.Comment: 10 pages, 6 figure
Three-body breakup within the fully discretized Faddeev equations
A novel approach is developed to find the three-body breakup amplitudes and
cross sections within the modified Faddeev equation framework. The method is
based on the lattice-like discretization of the three-body continuum with a
three-body stationary wave-packet basis in momentum space. The approach makes
it possible to simplify drastically all the three- and few-body breakup
calculations due to discrete wave-packet representations for the few-body
continuum and simultaneous lattice representation for all the scattering
operators entering the integral equation kernels. As a result, the few-body
breakup can be treated as a particular case of multi-channel scattering in
which part of the channels represents the true few-body continuum states. As an
illustration for the novel approach, an accurate calculations for the
three-body breakup process with non-local and local
interactions are calculated. The results obtained reproduce nicely the
benchmark calculation results using the traditional Faddeev scheme which
requires much more tedious and time-consuming calculations.Comment: 17 pages, 13 figure
Efficient dynamical nuclear polarization in quantum dots: Temperature dependence
We investigate in micro-photoluminescence experiments the dynamical nuclear
polarization in individual InGaAs quantum dots. Experiments carried out in an
applied magnetic field of 2T show that the nuclear polarization achieved
through the optical pumping of electron spins is increasing with the sample
temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the
dependence of the Overhauser shift on the spin polarization of the optically
injected electron as a function of temperature enables us to identify the main
reasons for this increase.Comment: 5 pages, 3 figure
Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots
We show that optical pumping of electron spins in individual InGaAs quantum
dots leads to strong nuclear polarisation that we measure via the Overhauser
shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find
a strongly non-monotonous dependence of the OHS on the applied magnetic field,
with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We
observe that the OHS is larger for nuclear fields anti-parallel to the external
field than in the parallel configuration. A bistability in the dependence of
the OHS on the spin polarization of the optically injected electrons is found.
All our findings are qualitatively understood with a model based on a simple
perturbative approach.Comment: Phys Rev B (in press
Electron spin quantum beats in positively charged quantum dots: nuclear field effects
We have studied the electron spin coherence in an ensemble of positively
charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that
two main contributions must be taken into account to explain the damping of the
circular polarization oscillations. The first one is due to the nuclear field
fluctuations from dot to dot experienced by the electron spin. The second one
is due to the dispersion of the transverse electron Lande g-factor, due to the
inherent inhomogeneity of the system, and leads to a field dependent
contribution to the damping. We have developed a model taking into account both
contributions, which is in good agreement with the experimental data. This
enables us to extract the pure contribution to dephasing due to the nuclei.Comment: 10 pages, 6 figure
On the Flavor Structure of the Constituent Quark
We discuss the dressing of constituent quarks with a pseudoscalar meson cloud
within the effective chiral quark model. SU(3) flavor symmetry breaking effects
are included explicitly. Our results are compared with those of the traditional
meson cloud approach in which pions are coupled to the nucleon. The pionic
dressing of the constituent quarks explains the experimentally observed
violation of the Gottfried Sum Rule and leads to an enhanced nonperturbative
sea of quark-antiquark pairs in the constituent quark and consequently in the
nucleon. We find 2.5 times more pions and 10-15 times more kaons in the nucleon
than in the traditional picture.Comment: 7 pages, LaTeX, 4 Postscript figures, to appear in J. Phys.
Neutrino Oscillations and R-parity Violating Supersymmetry
Using the neutrino oscillations and neutrinoless double beta decay
experimental data we reconstructed an upper limit for the three generation
neutrino mass matrix. We compared this matrix with the predictions of the
minimal supersymmetric(SUSY) model with R-parity violation(\rp) and extracted
stringent limits on trilinear \rp coupling constants . Introducing an additional flavor symmetry which had
been successful in explaining to relate various \rp parameters. In this model
we found a unique scenario for the neutrino masses and the \rp couplings
compatible with the neutrino oscillation data. Then we derived predictions for
certain experimentally interesting observables.Comment: 19 pages, 1 figure; additional references included, minor corrections
and typos fixed. Version to appear in Nucl.Phys.
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