454 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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Dependence of two-nucleon momentum densities on total pair momentum
Two-nucleon momentum distributions are calculated for the ground states of
3He and 4He as a function of the nucleons' relative and total momenta. We use
variational Monte Carlo wave functions derived from a realistic Hamiltonian
with two- and three-nucleon potentials. The momentum distribution of pp pairs
is found to be much smaller than that of pn pairs for values of the relative
momentum in the range (300--500) MeV/c and vanishing total momentum. However,
as the total momentum increases to 400 MeV/c, the ratio of pp to pn pairs in
this relative momentum range grows and approaches the limit 1/2 for 3He and 1/4
for 4He, corresponding to the ratio of pp to pn pairs in these nuclei. This
behavior should be easily observable in two-nucleon knock-out processes, such
as A(e,e'pN).Comment: 3 pages, 3 figure
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