6,734 research outputs found
Nuclear Breakup of Borromean Nuclei
We study the eikonal model for the nuclear-induced breakup of Borromean
nuclei, using Li11 and He6 as examples. The full eikonal model is difficult to
realize because of six-dimensional integrals, but a number of simplifying
approximations are found to be accurate. The integrated diffractive and
one-nucleon stripping cross sections are rather insensitive to the
neutron-neutron correlation, but the two-nucleon stripping does show some
dependence on the correlation. The distribution of excitation energy in the
neutron-core final state in one-neutron stripping reactions is quite sensitive
to the shell structure of the halo wave function. Experimental data favor
models with comparable amounts of s- and p-wave in the Li11 halo.Comment: 34 pages REVTeX, 14 postscript figures. Small changes in comparison
with experimen
Systematic approach to leptogenesis in nonequilibrium QFT: vertex contribution to the CP-violating parameter
The generation of a baryon asymmetry via leptogenesis is usually studied by
means of classical kinetic equations whose applicability to processes in the
hot and expanding early universe is questionable. The approximations implied by
the state-of-the-art description can be tested in a first-principle approach
based on nonequilibrium field theory techniques. Here, we apply the
Schwinger-Keldysh/Kadanoff-Baym formalism to a simple toy model of
leptogenesis. We find that, within the toy model, medium effects increase the
vertex contribution to the CP-violating parameter. At high temperatures it is a
few times larger than in vacuum and asymptotically reaches the vacuum value as
the temperature decreases. Contrary to the results obtained earlier in the
framework of thermal field theory, the corrections are only linear in the
particle number densities. An important feature of the Kadanoff-Baym formalism
is that it is free of the double-counting problem, i.e. no need for real
intermediate state subtraction arises. In particular, this means that the
structure of the equations automatically ensures that the asymmetry vanishes in
equilibrium. These results give a first glimpse into a number of new and
interesting effects that can be studied in the framework of nonequilibrium
field theory.Comment: 27 pages, 21 figure
Wannier-Stark resonances in optical and semiconductor superlattices
In this work, we discuss the resonance states of a quantum particle in a
periodic potential plus a static force. Originally this problem was formulated
for a crystal electron subject to a static electric field and it is nowadays
known as the Wannier-Stark problem. We describe a novel approach to the
Wannier-Stark problem developed in recent years. This approach allows to
compute the complex energy spectrum of a Wannier-Stark system as the poles of a
rigorously constructed scattering matrix and solves the Wannier-Stark problem
without any approximation. The suggested method is very efficient from the
numerical point of view and has proven to be a powerful analytic tool for
Wannier-Stark resonances appearing in different physical systems such as
optical lattices or semiconductor superlattices.Comment: 94 pages, 41 figures, typos corrected, references adde
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