1,042 research outputs found
Dependence of nuclear binding on hadronic mass variation
We examine how the binding of light () nuclei depends on possible
variations of hadronic masses, including meson, nucleon, and nucleon-resonance
masses. Small variations in hadronic masses may have occurred over time; the
present results can help evaluate the consequences for big bang
nucleosynthesis. Larger variations may be relevant to current attempts to
extrapolate properties of nucleon-nucleon interactions from lattice QCD
calculations. Results are presented as derivatives of the energy with respect
to the different masses so they can be combined with different predictions of
the hadronic mass-dependence on the underlying current-quark mass . As an
example, we employ a particular set of relations obtained from a study of
hadron masses and sigma terms based on Dyson-Schwinger equations and a
Poincar\'{e}-covariant Faddeev equation for confined quarks and diquarks. We
find that nuclear binding decreases moderately rapidly as the quark mass
increases, with the deuteron becoming unbound when the pion mass is increased
by 60% (corresponding to an increase in of 2.5).
In the other direction, the dineutron becomes bound if the pion mass is
decreased by 15% (corresponding to a reduction of by 30%). If
we interpret the disagreement between big bang nucleosynthesis calculations and
measurements to be the result of variation in , we obtain an estimate
where (the expected
accuracy in is about a factor of 2). The result is dominated by Li
data.Comment: 28 pages including 3 figures v2:additional citations/acknowledgments
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Nuclear matter hole spectral function in the Bethe-Brueckner-Goldstone approach
The hole spectral function is calculated in nuclear matter to assess the
relevance of nucleon-nucleon short range correlations. The calculation is
carried out within the Brueckner scheme of many-body theory by using several
nucleon-nucleon realistic interactions. Results are compared with other
approaches based on variational methods and transport theory. Discrepancies
appear in the high energy region, which is sensitive to short range
correlations, and are due to the different many-body treatment more than to the
specific N-N interaction used. Another conclusion is that the momentum
dependence of the G-matrix should be taken into account in any self consistent
approach.Comment: 7 pages, 5 figure
Tensor correlations in the Unitary Correlation Operator Method
We present a unitary correlation operator that explicitly induces into shell
model type many-body states short ranged two-body correlations caused by the
strong repulsive core and the pronounced tensor part of the nucleon-nucleon
interaction. Alternatively an effective Hamiltonian can be defined by applying
this unitary correlator to the realistic nucleon-nucleon interaction.
The momentum space representation shows that realistic interactions which
differ in their short range behaviour are mapped on the same correlated
Hamiltonian, indicating a successful provision for the correlations at high
momenta. Calculations for He4 using the one- and two-body part of the
correlated Hamiltonian compare favorably with exact many-body methods. For
heavier nuclei like O16 and Ca40 where exact many-body calculations are not
possible we compare our results with other approximations. The correlated
single-particle momentum distributions describe the occupation of states above
the Fermi momentum. The Unitary Correlation Operator Method (UCOM) can be used
in mean-field and shell model configuration spaces that are not able to
describe these repulsive and tensor correlations explicitly.Comment: 73 pages, 65 figure
Nuclei of Double-Charm Hyperons
The ground states of double-charm hyperons form a spin 1/2 isospin 1/2
multiplet analogous to that of nucleons. Their main strong interaction may be
inferred directly from the corresponding nucleon-nucleon interaction by
multiplication of the interaction components by the appropriate fractional
difference between interaction strengths for pairs of light flavor quarks and
pairs of triplets, e.g. nucleons, of light flavor quarks. By construction of
the interaction between the recently discovered double-charm hyperons by this
method from several realistic nucleon-nucleon interaction models it is shown
that double-charm hyperons are likely to form bound (or possibly meta-stable)
states akin to the deuteron in the spin triplet state. Double beauty baryons
would form corresponding deeply bound states. Nucleons and double charm
(beauty) hyperons will also form bound states. The existence of hypernuclei
with double-charm and double-beauty hyperons, which are stable against the
strong decay, is very likely.Comment: Revised version. Conclusions unchange
Photodisintegration of Three-Body Nuclei with Realistic 2N and 3N Forces
Total photonuclear absorption cross sections of H and He are studied
using realistic NN and NNN forces. Final state interactions are fully included.
Two NN potential models, the AV14 and the r-space Bonn-A potentials, are
considered. For the NNN forces the Urbana-VIII and Tucson-Melbourne models are
employed. We find the cross section to be sensitive to nuclear dynamics. Of
particular interest in this work is the effect which NNN forces have on the
cross section. The addition of NNN forces not only lowers the peak height but
increases the cross section beyond 70 MeV by roughly 15%. Cross sections are
computed using the Lorentz integral transform method.Comment: Results for Bonn potential with model Bonn rA instead of model rB.
The Bonn rB results contained a small inexactness. After the correction it
turned out that Bonn rA is more suited for our purpose because it leads to a
binding energy of 8.15 MeV (about 0.25 MeV more than Bonn rB). In addition
the results for the other realistic potentials models are improved at low
energies (HH expansion was not completely convergent for the low-energy
results). LaTeX, 8 pages, 4 ps figure
Correlation effects on the weak response of nuclear matter
The consistent description of the nuclear response at low and high momentum
transfer requires a unified dynamical model, suitable to account for both
short- and long-range correlation effects. We report the results of a study of
the charged current weak response of symmetric nuclear matter, carried out
using an effective interaction obtained from a realistic model of the
nucleon-nucleon force within the formalism of correlated basis functions. Our
approach allows for a clear identification of the kinematical regions in which
different interaction effects dominate
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