637 research outputs found
A Semiclassical Approach to Level Crossing in Supersymmetric Quantum Mechanics
Much use has been made of the techniques of supersymmetric quantum mechanics
(SUSY QM) for studying bound-state problems characterized by a superpotential
. Under the analytic continuation , a pair of
superpartner bound-state problems is transformed into a two-state
level-crossing problem in the continuum. The description of matter-enhanced
neutrino flavor oscillations involves a level-crossing problem. We treat this
with the techniques of supersymmetric quantum mechanics. For the benefit of
those not familiar with neutrino oscillations and their description, enough
details are given to make the rest of the paper understandable. Many other
level-crossing problems in physics are of exactly the same form. Particular
attention is given to the fact that different semiclassical techniques yield
different results. The best result is obtained with a uniform approximation
that explicitly recognizes the supersymmetric nature of the system.Comment: 15 pages, Latex with lamuphys and psfig macros. Talk by first Author
at the UIC "Supersymmetry and Integrable Models Workshop", Chicago, June
12-14, 1997; proceedings to be published in Springer Lecture Notes in
Physics, H. Aratyn et al., eds. This paper also available at
http://nucth.physics.wisc.edu/preprint
Neutrino Physics and Nuclear Axial Two-Body Interactions
We consider the counter-term describing isoscalar axial two-body currents in
the nucleon-nucleon interaction, L1A, in the effective field theory approach.
We determine this quantity using the solar neutrino data. We investigate the
variation of L1A when different sets of data are used.Comment: 8 pages with 4 figures. To be published in the Proceedings of the
Conference "Blueprints For The Nucleus: From First Principles to Collective
Motion" held at Feza Gursey Institute, Istanbul, Turkey; May 17 -22, 200
Partition Functions in Statistical Mechanics, Symmetric Functions, and Group Representations
Partition functions for non-interacting particles are known to be symmetric
functions. It is shown that powerful group-theoretical techniques can be used
not only to derive these relationships, but also to significantly simplify
calculation of the partition functions for particles that carry internal
quantum numbers. The partition function is shown to be a sum of one or more
group characters. The utility of character expansions in calculating the
partition functions is explored. Several examples are given to illustrate these
techniques.Comment: 16 pages of RevTe
Description of Nuclear Structure Effects in Subbarrier Fusion by the Interacting Boson Model
Recent theoretical developments in using the Interacting Boson Model to
describe nuclear structure effects in fusion reactions below the Coulomb
barrier are reviewed. Methods dealing with linear and all orders coupling
between the nuclear excitations and the translational motion are discussed, and
the latter is found to lead to a better description of the barrier distribution
data. A systematic study of the available data (cross sections, barrier and
spin distributions) in rare-earth nuclei is presented.Comment: 9 pages + 2 Figures (in eps form). To be published in the Proceedings
of the FUSION97 Conference, South Durras, Australia, March 1997 (J. Phys. G).
Full text and figures are also available at
http://nucth.physics.wisc.edu/preprints/mad-nt-97-01.abs.htm
Neutrinos in Cosmology and Astrophysics
We briefly review the recent developments in neutrino physics and
astrophysics which have import for frontline research in nuclear physics. These
developments, we argue, tie nuclear physics to exciting developments in
observational cosmology and astrophysics in new ways. Moreover, the behavior of
neutrinos in dense matter is itself a fundamental problem in many-body quantum
mechanics, in some ways akin to well-known issues in nuclear matter and nuclei,
and in some ways radically different, especially because of nonlinearity and
quantum de-coherence. The self-interacting neutrino gas is the only many body
system driven by the weak interactions.Comment: 7 pages, 1 figur
Impact of the Neutrino Magnetic Moment on the Neutrino Fluxes and the Electron Fraction in core-collapse Supernovae
We explore the effect of the neutrino magnetic moment on neutrino scattering
with matter in a core-collapse Supernova. We study the impact both on the
neutrino fluxes and on the electron fraction. We find that sizeable
modifications require very large magnetic moments both for Dirac and Majorana
neutrinos.Comment: 7 pages, 6 figure
Probing anharmonic properties of nuclear surface vibration by heavy-ion fusion reactions
Describing fusion reactions between ^{16}O and ^{154}Dy and, between ^{16}O
and ^{144}Sm by the and interacting boson model, we show that
heavy-ion fusion reactions are strongly affected by anharmonic properties of
nuclear surface vibrations and nuclear shape, and thus provide a powerful
method to study details of nuclear structure and dynamics.Comment: 8 pages, 5 figures, To be published in the Proceedings of the FUSION
97 Conference, South Durras, Australia, March 1997 (J. Phys. G
Majorana Neutrino Magnetic Moment and Neutrino Decoupling in Big Bang Nucleosynthesis
We examine the physics of the early universe when Majorana neutrinos
(electron neutrino, muon neutrino, tau neutrino) possess transition magnetic
moments. These extra couplings beyond the usual weak interaction couplings
alter the way neutrinos decouple from the plasma of electrons/positrons and
photons. We calculate how transition magnetic moment couplings modify neutrino
decoupling temperatures, and then use a full weak, strong, and electromagnetic
reaction network to compute corresponding changes in Big Bang Nucleosynthesis
abundance yields. We find that light element abundances and other cosmological
parameters are sensitive to magnetic couplings on the order of 10^{-10} Bohr
magnetons. Given the recent analysis of sub-MeV Borexino data which constrains
Majorana moments to the order of 10^{-11} Bohr magnetons or less, we find that
changes in cosmological parameters from magnetic contributions to neutrino
decoupling temperatures are below the level of upcoming precision observations.Comment: 19 pages, 9 figure
Relations between fusion cross sections and average angular momenta
We study the relations between moments of fusion cross sections and averages
of angular momentum. The role of the centrifugal barrier and the target
deformation in determining the effective barrier radius are clarified. A simple
method for extracting average angular momentum from fusion cross sections is
demonstrated using numerical examples as well as actual data.Comment: 16 REVTeX pages plus 8 included Postscript figures (uses the epsf
macro); submitted to Phys. Rev. C; also available at
http://nucth.physics.wisc.edu/preprint
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