310 research outputs found
Sterile neutrinos in neutrinoless double beta decay
We study possible contribution of the Majorana neutrino mass eigenstate
dominated by a sterile neutrino component to neutrinoless double beta
() decay. From the current experimental lower bound on the
-decay half-life of Ge we derive stringent constraints
on the mixing in a wide region of the values of mass. We
discuss cosmological and astrophysical status of in this mass region.Comment: 6 pages, 1 figure; v2 added comments and reference
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
Heavy Ion Collisions and the Density Dependence of the Local Mean Field
We study the effect of the density dependence of the scalar and the vector
part of the nucleonic self-energy in Relativistic Quantum Molecular Dynamics
(RQMD) on observables like the transversal flow and the rapidity distribution.
The stability of nuclei in RQMD is greatly improved if the density dependence
is included in the self-energies compared to a calculation assuming always
saturation density of nuclear matter. Different approaches are studied: The
main results are calculated with self-energies extracted from a
Dirac-Br\"uckner-Hartree-Fock G-matrix of a one boson exchange model, i.e. the
Bonn potential. These results are compared with those obtained by a
generalization of static Skyrme force, with calculations in the simple linear
Walecka model and results of the Br\"uckner-Hartree-Fock G-matrix of the Reid
soft core potential. The transversal flow is very sensitive to these different
approaches. A comparison with the data is given.Comment: LaTex-file, 13 pages, 5 figures (available upon request), submitted
to Nuclear Physics
Scalar meson mediated nuclear mu-e conversion
We study the nuclear mu-e conversion in the general framework of the
effective Lagrangian approach without referring to any specific realization of
the physics beyond the standard model (SM) responsible for lepton flavor
violation (LFV). We analyze the role of scalar meson exchange between the
lepton and nucleon currents and show its relevance for the coherent channel of
mu-e conversion. We show that this mechanism introduces modifications in the
predicted mu-e conversion rates in comparison with the conventional direct
nucleon mechanism, based on the contact type interactions of the nucleon
currents with the LFV leptonic current. We derive from the experimental data
lower limits on the mass scales of the generic LFV lepton-quark contact terms
and demonstrate that they are more stringent than the similar limits existing
in the literature.Comment: 14 pages, 1 figur
Exciton Valley Dynamics probed by Kerr Rotation in WSe2 Monolayers
We have experimentally studied the pump-probe Kerr rotation dynamics in
WSe monolayers. This yields a direct measurement of the exciton valley
depolarization time . At T=4K, we find ps, a fast
relaxation time resulting from the strong electron-hole Coulomb exchange
interaction in bright excitons. The exciton valley depolarization time
decreases significantly when the lattice temperature increases with
being as short as 1.5ps at 125K. The temperature dependence is well explained
by the developed theory taking into account the exchange interaction and a fast
exciton scattering time on short-range potentials.Comment: 5 pages, 3 figure
Proton-neutron pairing in the deformed BCS approach
We examine isovector and isoscalar proton-neutron pairing correlations for
the ground state of even-even Ge isotopes with mass number A=64-76 within the
deformed BCS approach. For N=Z 64Ge the BCS solution with only T=0
proton-neutron pairs is found. For other nuclear systems (N>Z) a coexistence of
a T=0 and T=1 pairs in the BCS wave function is observed. A problem of fixing
of strengths of isoscalar and isovector pairing interactions is addressed. A
dependence of number of like and unlike pairs in the BCS ground state on the
difference between number of neutrons and protons is discussed. We found that
for nuclei with N much bigger than Z the effect of proton-neutron pairing is
small but not negligible.Comment: 24 pages, 6 figure
Effective Lagrangian approach to nuclear mu-e conversion and the role of vector mesons
We study nuclear mu-e conversion in the general framework of an effective
Lagrangian approach without referring to any specific realization of the
physics beyond the standard model (SM) responsible for lepton flavor violation
(LFV). We examine the impact of a specific hadronization prescription on the
analysis of new physics in nuclear mu-e conversion and stress the importance of
vector meson exchange between lepton and nucleon currents. A new issue of this
mechanism is the presence of the strange quark vector current contribution
induced by the phi meson. This allows us to extract new limits on the LFV
lepton-quark effective couplings from the existing experimental data.Comment: 19 pages, 3 figures, to be published in Phys Rev
Influence of the pion-nucleon interaction on the collective pion flow in heavy ion reactions
We investigate the influence of the real part of the in-medium pion optical
potential on the pion dynamics in intermediate energy heavy ion reactions at 1
GeV/A. For different models, i.e. a phenomenological model and the
--hole model, a pionic potential is extracted from the dispersion
relation and used in Quantum Molecular Dynamics calculations. In addition with
the inelastic scattering processes we thus take care of both, real and
imaginary part of the pion optical potential. A strong influence of the real
pionic potential on the pion in-plane flow is observed. In general such a
potential has the tendency to reduce the anticorrelation of pion and nucleon
flow in non-central collisions.Comment: 12 pages Latex, 4 PS-figure
Robust optical emission polarization in MoS2 monolayers through selective valley excitation
We report polarization resolved photoluminescence from monolayer MoS2, a
two-dimensional, non-centrosymmetric crystal with direct energy gaps at two
different valleys in momentum space. The inherent chiral optical selectivity
allows exciting one of these valleys and close to 90% polarized emission at 4K
is observed with 40% polarization remaining at 300K. The high polarization
degree of the emission remains unchanged in transverse magnetic fields up to 9T
indicating robust, selective valley excitation.Comment: 5 pages, 3 figure
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