21,336 research outputs found
Three-body spin-orbit forces from chiral two-pion exchange
Using chiral perturbation theory, we calculate the density-dependent
spin-orbit coupling generated by the two-pion exchange three-nucleon
interaction involving virtual -isobar excitation. From the
corresponding three-loop Hartree and Fock diagrams we obtain an isoscalar
spin-orbit strength which amounts at nuclear matter
saturation density to about half of the empirical value of MeVfm. The
associated isovector spin-orbit strength comes out about a
factor of 20 smaller. Interestingly, this three-body spin-orbit coupling is not
a relativistic effect but independent of the nucleon mass . Furthermore, we
calculate the three-body spin-orbit coupling generated by two-pion exchange on
the basis of the most general chiral -contact interaction. We find
similar (numerical) results for the isoscalar and isovector spin-orbit
strengths and with a strong dominance of
the p-wave part of the -contact interaction and the Hartree
contribution.Comment: 8 pages, 4figure, published in : Physical Review C68, 054001 (2003
Chiral pion-nucleon dynamics in finite nuclei: spin-isospin excitations
The nuclear density functional framework, based on chiral dynamics and the
symmetry breaking pattern of low-energy QCD, is extended to the description of
collective nuclear excitations. Starting from the relativistic point-coupling
Lagrangian previously introduced [Nucl. Phys. A770 (2006) 1], the
proton-neutron (quasiparticle) random phase approximation is formulated and
applied to investigate the role of chiral pion-nucleon dynamics in excitation
modes involving spin and isospin degrees of freedom, e.g. isobaric analog
states and Gamow-Teller resonances.Comment: 17 pages, 6 figures, elsart class. Minor revisions, Nuclear Physics A
in prin
Symmetrization and enhancement of the continuous Morlet transform
The forward and inverse wavelet transform using the continuous Morlet basis
may be symmetrized by using an appropriate normalization factor. The loss of
response due to wavelet truncation is addressed through a renormalization of
the wavelet based on power. The spectral density has physical units which may
be related to the squared amplitude of the signal, as do its margins the mean
wavelet power and the integrated instant power, giving a quantitative estimate
of the power density with temporal resolution. Deconvolution with the wavelet
response matrix reduces the spectral leakage and produces an enhanced wavelet
spectrum providing maximum resolution of the harmonic content of a signal.
Applications to data analysis are discussed.Comment: 12 pages, 8 figures, 2 tables, minor revision, final versio
Nuclear Many-Body Dynamics constrained by QCD and Chiral Symmetry
We present a novel description of nuclear many-body systems, both for nuclear
matter and finite nuclei, emphasizing the connection with the condensate
structure of the QCD ground state and spontaneous chiral symmetry breaking.
Lorentz scalar and vector mean-fields are introduced in accordance with QCD sum
rules. Nuclear binding arises from pionic fluctuations, using in-medium chiral
perturbation theory up to three-loop order. Ground state properties of O
and Ca are calculated. The built-in QCD constraints reduce the number of
input parameters significantly in comparison with purely phenomenological
relativistic mean-field approaches.Comment: 6 pages, 3 figures, to be published in European Physical Journal
Spin-orbit coupling in nuclei and realistic nucleon-nucleon potentials
We analyze the spin-orbit coupling term in the nuclear energy density
functional in terms of a zero-range NN-contact interaction and finite-range
contributions from two-pion exchange. We show that the strength of the
spin-orbit contact interaction as extracted from high-precision nucleon-nucleon
potentials is in perfect agreement with that of phenomenological Skyrme forces
employed in non-relativistic nuclear structure calculations. Additional
long-range contributions from chiral two-pion exchange turn out to be
relatively small. These explicitly density-dependent contributions reduce the
ratio of the isovector to the isoscalar spin-orbit strength significantly below
the Skyrme value 1/3. We perform a similar analysis for the strength function
of the -term and find values not far from those of
phenomenological Skyrme parameterizations.Comment: 10 pages, 3 figures, accepted for publication in Physical Review C70
(2004
Three episodes of jet activity in the FRII radio galaxy B0925+420
We present Very Large Array images of a "Double-Double Radio Galaxy", a class
of objects in which two pairs of lobes are aligned either side of the nucleus.
In this object, B0925+420, we discover a third pair of lobes, close to the core
and again in alignment with the other lobes. This first-known "Triple-Double"
object strongly increases the likelihood that these lobes represent mutiple
episodes of jet activity, as opposed to knots in an underlying jet. We model
the lobes in terms of their dynamical evolution. We find that the inner pair of
lobes is consistent with the outer pair having been displaced buoyantly by the
ambient medium. The middle pair of lobes is more problematic - to the extent
where an alternative model interpreting the middle and inner "lobes" as
additional bow shocks within the outer lobes may be more appropriate - and we
discuss the implications of this on our understanding of the density of the
ambient medium.Comment: Accepted for publication in MNRAS. Figure 2 is best viewed in colou
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