286 research outputs found
Search for long-lived states in antiprotonic lithium
The spectrum of the (L_i^3 + p-bar + 2e) four-body system was calculated in
an adiabatic approach. The two-electron energies were approximated by a sum of
two single-electron effective charge two-center energies as suggested in [6].
While the structure of the spectrum does not exclude the existence of
long-lived states, their experimental observability is still to be clarified
Formulae for partial widths derived from the Lindblad equation
A method for calculating partial widths of auto-ionizing states is proposed.
It combines either a complex absorbing potential or exterior complex scaling
with the Lindblad equation. The corresponding classical rate equations are
reproduced, and the trace conservation inherent in the Lindblad equation
ensures that the partial widths sums up to the total width of the initial
auto-ionizing state
Analytic structure and power series expansion of the Jost function for the two-dimensional problem
For a two-dimensional quantum-mechanical problem, we obtain a generalized
power series expansion of the S-matrix that can be done near an arbitrary point
on the Riemann surface of the energy, similar to the standard effective-range
expansion. In order to do this, we consider the Jost function and analytically
factorize its momentum dependence that causes the Jost function to be a multivalued
function. The remaining single-valued function of the energy is then
expanded in the power series near an arbitrary point in the complex energy
plane. A systematic and accurate procedure has been developed for calculating
the expansion coefficients. This makes it possible to obtain a semi-analytic
expression for the Jost function (and therefore for the S-matrix) near an arbitrary
point on the Riemann surface and use it, for example, to locate the spectral
points (bound and resonant states) as the S-matrix poles. The method is applied
to a model similar to those used in the theory of quantum dots.http://www.iop.org/EJ/journal/JPhysAnf201
A method for extracting the resonance parameters from experimental cross-sections
Within the proposed method, a set of experimental data points are fitted using a
multi-channel S-matrix. Then the resonance parameters are located as its poles on an
appropriate sheet of the Riemann surface of the energy. The main advantage of the
method is that the S-matrix is constructed in such a way that it has proper analytic
structure, i.e. for any number of two-body channels, the branching at all the channel
thresholds is represented via exact analytic expressions in terms of the channel momenta.
The way the S-matrix is constructed makes it possible not only to locate multi-channel
resonances but also to extract their partial widths as well as to obtain the scattering cross-section in the channels for which no data are available. The efficiency of the
method is demonstrated by two model examples of a single-channel and a two-channel
problems, where known resonance parameters are rather accurately reproduced by fitting
the pseudo-data artificially generated using the corresponding potentials.http://www.worldscinet.com/ijmpehb201
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