9,952,835 research outputs found
Electron Scattering on 3He - a Playground to Test Nuclear Dynamics
The big spectrum of electron induced processes on 3He is illustrated by
several examples based on Faddeev calculations with modern nucleon-nucleon and
three-nucleon forces as well as exchange currents. The kinematical region is
restricted to a mostly nonrelativistic one where the three-nucleon c.m. energy
is below the pion production threshold and the three-momentum of the virtual
photon is sufficiently below the nucleon mass. Comparisons with available data
are shown and cases of agreement and disagreement are found. It is argued that
new and precise data are needed to systematically check the present day
dynamical ingredients.Comment: 27 pages, 24 figure
Exotic Baryons and Monopole Excitations in a Chiral Soliton Model
We compute the spectra of exotic pentaquarks and monopole excitations of the
low--lying and baryons in a chiral soliton model. Once the
low--lying baryon properties are fit, the other states are predicted without
any more adjustable parameters. This approach naturally leads to a scenario in
which the mass spectrum of the next to lowest--lying states is
fairly well approximated by the ideal mixing pattern of the
representation of flavor SU(3). We compare
our results to predictions obtained in other pictures for pentaquarks and
speculate about the spin--parity assignment for and Comment: 16 pages, 2 figures, 6 table
Compact stars in the standard model - and beyond
In the context of the standard model of particle physics, there is a definite
upper limit to the density of stable compact stars. However, if there is a
deeper layer of constituents, below that of quarks and leptons, stability may
be re-established far beyond this limiting density and a new class of compact
stars could exist. These objects would cause gravitational lensing of white
dwarfs and gamma-ray bursts, which might be observable as a diffraction pattern
in the spectrum. Such observations could provide means for obtaining new clues
about the fundamental particles and the origin of cold dark matter.Comment: 16 pages, 6 figures, contribution to the 42nd course of the
international school of subnuclear physics, 'How and where to go beyond the
standard model', Erice, Aug. 29 - Sep. 7, 200
Ratchet-Like Solitonic Transport in Quantum Hall Bilayers
The pseudo-spin model for double layer quantum Hall system with total landau
level filling factor is discussed. Unlike the "traditional" one where
interlayer voltage enters as static magnetic field along pseudo- spin hard
axis, in our model we consider applied interlayer voltage as a frequency of
precessing pseudo-magnetic field lying into the easy plane. It is shown that a
Landau-Lifshitz equation for the considered pseudo magnetic system well
describes existing experimental data. Besides that, the mentioned model
predicts novel directed intra-layer transport phenomenon in the system:
unidirectional intra-layer energy transport is realized due to interlayer
voltage induced motion of topological kinks. This effect could be observed
experimentally detecting counter-propagating intra-layer inhomogeneous charge
currents which are proportional to the interlayer voltage and total topological
charge of the pseudo-spin system.Comment: 4 pages, 4 figure
Orbital contribution to the magnetic properties of nanowires: Is the orbital polarization ansatz justified?
We show that considerable orbital magnetic moments and magneto-crystalline
anisotropy energies are obtained for a Fe monatomic wire described in a
tight-binding method with intra-atomic electronic interactions treated in a
full Hartree Fock (HF) decoupling scheme. Even-though the use of the orbital
polarization ansatz with simplified Hamiltonians leads to fairly good results
when the spin magnetization is saturated this is not the case of unsaturated
systems. We conclude that the full HF scheme is necessary to investigate low
dimensional systems
Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0
Soft photons inside hadronic jets converted in front of the DELPHI main
tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the
kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to
the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the
experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/-
0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected
level of the inner hadronic bremsstrahlung (which is not included in the Monte
Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the
excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8),
which is similar in strength to the anomalous soft photon signal observed in
fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.
NN final-state interaction in two-nucleon knockout from
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in electro- and photoinduced two-nucleon knockout from has
been investigated perturbatively. It turns out that the effect of NN-FSI
depends on the kinematics and on the type of reaction considered. The effect is
generally larger in pp- than in pn-knockout and in electron induced than in
photoinduced reactions.
In superparallel kinematics NN-FSI leads in the channel to a
strong increase of the cross section, that is mainly due to a strong
enhancement of the -current contribution. In pn-emission, however, this
effect is partially cancelled by a destructive interference with the seagull
current. For photoreactions NN-FSI is considerably reduced in superparallel
kinematics and can be practically negligible in specific kinematics.Comment: 16 pages, 9 figure
Microscopic Models of Heavy Ion Interactions
An introduction to dynamical microscopic models of hadronic and nuclear
interactions is presented. Special emphasis is put in the relation between
multiparticle production and total cross-section contributions. In heavy ion
collisions, some observables, considered as signals of the production of a
Quark Gluon Plasma (QGP), are studied. It is shown that they can only be
described if final state interactions are introduced. It is argued that the
cross-sections required are too small to drive the system to thermal
equilibrium within the duration time of the final state interaction.Comment: 39 pages, 18 figures. Lectures at VIII Hispalensis International
Summer School, Seville (Spain), to be published by Springer Verla
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