8,696 research outputs found
Discrete Hubbard-Stratonovich transformations for systems with orbital degeneracy
A discrete Hubbard-Stratonovich transformation is presented for systems with
an orbital degeneracy and a Hubbard Coulomb interaction without multiplet
effects. An exact transformation is obtained by introducing an external field
which takes values. Alternative approximate transformations are
presented, where the field takes fewer values, for instance two values
corresponding to an Ising spin.Comment: 4 pages, revtex, 1 eps figure, additional material avalable at
http://librix.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
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
Selection rules in the double beta decay of deformed nuclei
The 2 nu double beta decay half-lives of six nuclei, whose decays were
previously reported as theoretically forbidden, are calculated by including the
pairing interaction, which mixes different occupations and opens up the
possibility of the decay. All allowed channels for the 0 nu double beta decay
are also computed. The estimated 2 nu double beta half-lives suggest that
measurements in 244Pu may find positive signals, and that planned experiments
would succeed in detecting the 2 nu double beta decay in 160Gd. Limits for the
zero neutrino mode, in the analyzed deformed emitters, are predicted.Comment: 4 pages, 4 table
Double beta decay of : the deformed limit
The double beta decay of to the ground state and excited states of
is analysed in the context of the pseudo SU(3) scheme. The results
of this deformed limit are compared with the vibrational one based on the QRPA
formalism. Consistency between the deformed limit and the experimental
information is found for various transitions, although, in this
approximation some energies and B(E2) intensities cannot reproduced.Comment: 16 pages, revtex, no figures. Submmitted to Phys. Rev.
Collider signatures of sneutrino cold dark matter
Decays of sneutrinos are considered in the case that in the presence of lepton-number violation in the sneutrino sector the lighter tau-sneutrino is the Lightest Supersymmetric Particle and the Cold Dark Matter in the Universe. In such circumstances the signals from sparticle decays differ considerably from the 'standard' case where the lightest neutralino is the Lightest Supersymmetric Particle and it is found that in a wide range of parameters compatible with the sneutrino Cold Dark Matter hypothesis signatures characteristic for such a scenario should be easily observable at for example a Next Linear Collider
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