385 research outputs found
Radiative double electron capture by bare nucleus with emission of one photon
Calculation of the cross-section for the process of double electron capture
by bare nucleus with emission of a single photon is presented. The double
electron capture is evaluated within the framework of Quantum Electrodynamics
(QED). Line-Profile Approach (LPA) is employed. Since the radiative double
electron capture is governed by the electron correlation, corrections to the
interelectron interaction were calculated with high accuracy, partly to all
orders of the perturbation theory
Automatic Generation of Matrix Element Derivatives for Tight Binding Models
Tight binding (TB) models are one approach to the quantum mechanical many
particle problem. An important role in TB models is played by hopping and
overlap matrix elements between the orbitals on two atoms, which of course
depend on the relative positions of the atoms involved. This dependence can be
expressed with the help of Slater-Koster parameters, which are usually taken
from tables. Recently, a way to generate these tables automatically was
published. If TB approaches are applied to simulations of the dynamics of a
system, also derivatives of matrix elements can appear. In this work we give
general expressions for first and second derivatives of such matrix elements.
Implemented in a computer program they obviate the need to type all the
required derivatives of all occuring matrix elements by hand.Comment: 11 pages, 2 figure
Virtual Resonant States in Two-Photon Decay Processes: Lower-Order Terms, Subtractions, and Physical Interpretations
We investigate the two-photon decay rate of a highly excited atomic state
which can decay to bound states of lower energy via cascade processes. We show
that a naive treatment of the process, based on the introduction of
phenomenological decay rates for the intermediate, resonant states, leads to
lower-order terms which need to be subtracted in order to obtain the coherent
two-photon correction to the decay rate. The sum of the lower-order terms is
exactly equal to the one-photon decay rate of the initial state, provided the
naive two-photon decay rates are summed over all available two-photon channels.
A quantum electrodynamics (QED) treatment of the problem leads to an
"automatic" subtraction of the lower-order terms.Comment: 8 pages, RevTe
Multipole expansions in four-dimensional hyperspherical harmonics
The technique of vector differentiation is applied to the problem of the
derivation of multipole expansions in four-dimensional space. Explicit
expressions for the multipole expansion of the function r^n C_j (\hr) with
\vvr=\vvr_1+\vvr_2 are given in terms of tensor products of two
hyperspherical harmonics depending on the unit vectors \hr_1 and \hr_2. The
multipole decomposition of the function (\vvr_1 \cdot \vvr_2)^n is also
derived. The proposed method can be easily generalised to the case of the space
with dimensionality larger than four. Several explicit expressions for the
four-dimensional Clebsch-Gordan coefficients with particular values of
parameters are presented in the closed form.Comment: 19 pages, no figure
Classification of finite dimensional uniserial representations of conformal Galilei algebras
With the aid of the -symbol, we classify all uniserial modules of
, where is the
Heisenberg Lie algebra of dimension .Comment: Some references added, introduction expanded, title change
-pairing interaction, number of states, and nine- sum rules of four identical particles
In this paper we study -pairing Hamiltonian and find that the sum of
eigenvalues of spin states equals sum of norm matrix elements within the
pair basis for four identical particles such as four fermions in a single-
shell or four bosons with spin . We relate number of states to sum rules of
nine- coefficients. We obtained sum rules for nine- coefficients
summing
over (1) even and , (2) even and odd , (3) odd and odd ,
and (4) both even and odd , where is a half integer and is an
integer.Comment: 6 pages, no figure, updated version, to be published. Physical Review
C, in pres
Shape coexistence in Lead isotopes in the interacting boson model with Gogny energy density functional
We investigate the emergence and evolution of shape coexistence in the
neutron-deficient Lead isotopes within the interacting boson model (IBM) plus
configuration mixing with microscopic input based on the Gogny energy density
functional (EDF). The microscopic potential energy surface obtained from the
constrained self-consistent Hartree-Fock-Bogoliubov method employing the
Gogny-D1M EDF is mapped onto the coherent-state expectation value of the
configuration-mixing IBM Hamiltonian. In this way, the parameters of the IBM
Hamiltonian are fixed for each of the three relevant configurations (spherical,
prolate and oblate) associated to the mean field minima. Subsequent
diagonalization of the Hamiltonian provides the excitation energy of the
low-lying states and transition strengths among them. The model predictions for
the level energies and evolving shape coexistence in the considered
Lead chain are consistent both with experiment and with the indications of the
Gogny-EDF energy surfaces.Comment: 12 pages, 6 figures, 1 tabl
AC Stark shift of the Cs microwave atomic clock transitions
We analyze the AC Stark shift of the Cs microwave atomic clock transition
theoretically and experimentally. Theoretical and experimental data are in a
good agreement with each other. Results indicate the absence of a magic
wavelength at which there would be no differential shift of the clock states
having zero projections of the total angular momentum
Interplay of p-d and d-d charge transfer transitions in rare-earth perovskite manganites
We have performed both theoretical and experimental study of optical response
of parent perovskite manganites RMnO_3 with a main goal to elucidate nature of
clearly visible optical features. Starting with a simple cluster model approach
we addressed the both one-center (p-d) and two-center (d-d) charge transfer
(CT) transitions, their polarization properties, the role played by structural
parameters, orbital mixing, and spin degree of freedom. Optical complex
dielectric function of single crystalline samples of RMnO_3 (R=La, Pr, Nd, Sm,
Eu) was measured by ellipsometric technique at room temperature in the spectral
range from 1.0 to 5.0 eV for two light polarizations: E \parallel c and E \perp
c. The comparative analysis of the spectral behavior of \varepsilon _1 and
\varepsilon _2 is believed to provide a more reliable assignment of spectral
features. We have found an overall agreement between experimental spectra and
theoretical predictions based on the theory of one-center p-d CT transitions
and inter-site d-d CT transitions. Our experimental data and theoretical
analysis evidence a dual nature of the dielectric gap in nominally
stoichiometric matrix of perovskite manganites RMnO_3, it is formed by a
superposition of forbidden or weak dipole allowed p-d CT transitions and
inter-site d-d CT transitions. In fact, the parent perovskite manganites RMnO_3
should rather be sorted neither into the CT insulator nor the Mott-Hubbard
insulator in the Zaanen, Sawatzky, Allen scheme.Comment: 20 pages, 6 figure
- …