1,101 research outputs found
Phase transitions with finite atom number in the Dicke Model
Two-level atoms interacting with a one mode cavity field at zero temperature
have order parameters which reflect the presence of a quantum phase transition
at a critical value of the atom-cavity coupling strength. Two popular examples
are the number of photons inside the cavity and the number of excited atoms.
Coherent states provide a mean field description, which becomes exact in the
thermodynamic limit. Employing symmetry adapted (SA) SU(2) coherent states
(SACS) the critical behavior can be described for a finite number of atoms. A
variation after projection treatment, involving a numerical minimization of the
SA energy surface, associates the finite number phase transition with a
discontinuity in the order parameters, which originates from a competition
between two local minima in the SA energy surface.Comment: 8 pages, 10 figures, Conference Proceedings of CEWQO-2012, to be
published as a Topical Issue of the journal Physica Script
Neutrinoless Double Beta Decay in Heavy Deformed Nuclei
The zero neutrino mode of the double beta decay in heavy deformed nuclei is
investigated in the framework of the pseudo SU(3) model, which has provided an
accurate description of collective nuclear structure and predicted half-lives
for the two neutrino mode in good agreement with experiments. In the case of
the calculated zero neutrino half-life is at least three orders of
magnitude greater than the two neutrino one, giving strong support of the
identification of the radiochemically determined half-life as being the two
neutrino double beta decay. For the zero neutrino matrix elements
are of the order of magnitude of, but lesser than, those evaluated using the
QRPA. This result confirms that different nuclear models produce similar zero
neutrino matrix elements, contrary to the two neutrino case. Using these pseudo
SU(3) results and the upper limit for the neutrino mass we estimate the
half-lives for six nuclei. An upper limit for majoron
coupling constant is extracted from the experimental data.Comment: 19 pages, LaTeX, 2 figures not included, availables as poscript files
upon reques
Searching for pairing energies in phase space
We obtain a representation of pairing energies in phase space, for the
Lipkin-Meshkov-Glick and general boson Bardeen-Cooper-Schrieffer pairing
models. This is done by means of a probability distribution of the quantum
state in phase space. In fact, we prove a correspondence between the points at
which this probability distribution vanishes and the pairing energies. In
principle, the vanishing of this probability distribution is experimentally
accessible and additionally gives a method to visualize pairing energies across
the model control parameter space. This result opens new ways to experimentally
approach quantum pairing systems.Comment: 5 pages, 4 figure
Double beta decay to excited states in Nd150
The pseudo SU(3) model is used to study the double beta decay of Nd150 to the
ground and excited states of Sm150 . Low lying collective excitations of Sm150
and its BE(2) intensities are well reproduced. Expressions for the two neutrino
double beta decay to excited states are developed and used to describe the
decay of Nd150 . The existence of selection rules which strongly restrict the
decay is discussed.Comment: 22 pages, LaTeX, 1 figure with Postscript file available under
request at [email protected]
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