2,151 research outputs found
Relativistic corrections to the long range interaction between closed shell atoms
The complete correction to the long range interaction between
neutral closed shell atoms is obtained, the relation to the asymptotic
expansion of the known short range interaction at the atomic scale is presented
and a general interaction potential which is valid in the whole range of the
inter atomic distances is constructed.Comment: 9 pages, accepted for Phys. Rev.
Relativistic, QED, and finite nuclear mass corrections for low-lying states of Li and Be
Accurate results for nonrelativistic energy, relativistic, QED, and finite
nuclear mass corrections are obtained for , and
states of the Li atom and Be ion. Our computational approach
uses the Hylleraas basis set with the analytic integration and recursion
relations. From comparison of experimental results for the isotope shifts to
theoretical predictions including nuclear polarizabilities, we obtain nuclear
charge radii for Li and Be isotopes.Comment: 19 pages, 8 tables, Phys. Rev. A in prin
The Determination of Nuclear Level Densities from Experimental Information -
A novel Information Theory based method for determining the density of states
from prior information is presented. The energy dependence of the density of
states is determined from the observed number of states per energy interval and
model calculations suggest that the method is sufficiently reliable to
calculate the thermal properties of nuclei over a reasonable temperature range.Comment: 7 pages + 6 eps figures, REVTEX 3.
Dispersive estimates for Schr\"odinger operators with point interactions in
The study of dispersive properties of Schr\"odinger operators with point
interactions is a fundamental tool for understanding the behavior of many body
quantum systems interacting with very short range potential, whose dynamics can
be approximated by non linear Schr\"odinger equations with singular
interactions. In this work we proved that, in the case of one point interaction
in , the perturbed Laplacian satisfies the same
estimates of the free Laplacian in the smaller regime . These
estimates are implied by a recent result concerning the boundedness of
the wave operators for the perturbed Laplacian. Our approach, however, is more
direct and relatively simple, and could potentially be useful to prove optimal
weighted estimates also in the regime .Comment: To appear on: "Advances in Quantum Mechanics: Contemporary Trends and
Open Problems", G. Dell'Antonio and A. Michelangeli eds., Springer-INdAM
series 201
Equations of motion approach to the spin-1/2 Ising model on the Bethe lattice
We exactly solve the ferromagnetic spin-1/2 Ising model on the Bethe lattice
in the presence of an external magnetic field by means of the equations of
motion method within the Green's function formalism. In particular, such an
approach is applied to an isomorphic model of localized Fermi particles
interacting via an intersite Coulomb interaction. A complete set of
eigenoperators is found together with the corresponding eigenvalues. The
Green's functions and the correlation functions are written in terms of a
finite set of parameters to be self-consistently determined. A procedure is
developed, that allows us to exactly fix the unknown parameters in the case of
a Bethe lattice with any coordination number z. Non-local correlation functions
up to four points are also provided together with a study of the relevant
thermodynamic quantities.Comment: RevTex, 29 pages, 13 figure
The Dynamics of the One-Dimensional Delta-Function Bose Gas
We give a method to solve the time-dependent Schroedinger equation for a
system of one-dimensional bosons interacting via a repulsive delta function
potential. The method uses the ideas of Bethe Ansatz but does not use the
spectral theory of the associated Hamiltonian
Quasiclassical calculations of BBR-induced depopulation rates and effective lifetimes of Rydberg nS, nP and nD alkali-metal atoms with n < 80
Rates of depopulation by blackbody radiation (BBR) and effective lifetimes of
alkali-metal \textit{nS}, \textit{n}P and \textit{nD} Rydberg states have been
calculated in a wide range of principal quantum numbers at the
ambient temperatures of 77, 300 and 600 K. Quasiclassical formulas were used to
calculate the radial matrix elements of the dipole transitions from Rydberg
states. Good agreement of our numerical results with the available theoretical
and experimental data has been found. We have also obtained simple analytical
formulas for estimates of effective lifetimes and BBR-induced depopulation
rates, which well agree with the numerical data.Comment: 12 pages, 6 figures, 8 tables. Typo in Eq.16 corrected in V2. Typos
in Eq.5 and Eq.9 corrected in V3. Error in calculation of Rb nP_{3/2}
effective lifetimes corrected in V4: see new data in Table II and Table VII,
Erratum to be published in PR
Foundation of an analytical proton beamlet model for inclusion in a general proton dose calculation system
We have developed a model for proton depth dose and lateral distributions
based on Monte Carlo calculations (GEANT4) and an integration procedure of the
Bethe-Bloch equation (BBE). The model accounts for the transport of primary and
secondary protons, the creation of recoil protons and heavy recoil nuclei as
well as lateral scattering of these contributions. The buildup, which is
experimentally observed in higher energy depth dose curves, is modeled by
inclusion of two different origins: 1. Secondary reaction protons with a
contribution of ca. 65 % of the buildup (for monoenergetic protons). 2. Landau
tails as well as Gaussian type of fluctuations for range straggling effects.
All parameters of the model for initially monoenergetic proton beams have been
obtained from Monte Carlo calculations or checked by them. Furthermore, there
are a few parameters, which can be obtained by fitting the model to measured
depth dose curves in order to describe individual characteristics of the
beamline - the most important being the initial energy spread. We find that the
free parameters of the depth dose model can be predicted for any intermediate
energy from a couple of measured curves.Comment: Eclipse implementatio
Ultrafast effective multi-level atom method for primordial hydrogen recombination
Cosmological hydrogen recombination has recently been the subject of renewed
attention because of its importance for predicting the power spectrum of cosmic
microwave background anisotropies. It has become clear that it is necessary to
account for a large number n >~ 100 of energy shells of the hydrogen atom,
separately following the angular momentum substates in order to obtain
sufficiently accurate recombination histories. However, the multi-level atom
codes that follow the populations of all these levels are computationally
expensive, limiting recent analyses to only a few points in parameter space. In
this paper, we present a new method for solving the multi-level atom
recombination problem, which splits the problem into a computationally
expensive atomic physics component that is independent of the cosmology, and an
ultrafast cosmological evolution component. The atomic physics component
follows the network of bound-bound and bound-free transitions among excited
states and computes the resulting effective transition rates for the small set
of "interface" states radiatively connected to the ground state. The
cosmological evolution component only follows the populations of the interface
states. By pre-tabulating the effective rates, we can reduce the recurring cost
of multi-level atom calculations by more than 5 orders of magnitude. The
resulting code is fast enough for inclusion in Markov Chain Monte Carlo
parameter estimation algorithms. It does not yet include the radiative transfer
or high-n two-photon processes considered in some recent papers. Further work
on analytic treatments for these effects will be required in order to produce a
recombination code usable for Planck data analysis.Comment: Version accepted by Phys. Rev. D. Proof of equivalence of effective
and standard MLA methods moved to the main text. Some rewording
Relativistic Reduced-Mass and Recoil Corrections to Vacuum Polarization in Muonic Hydrogen, Muonic Deuterium and Muonic Helium Ions
The reduced-mass dependence of relativistic and radiative effects in simple
muonic bound systems is investigated. The spin-dependent nuclear recoil
correction of order (Zalpha)^4 mu^3/m_N^2 is evaluated for muonic hydrogen and
deuterium, and muonic helium ions (mu is the reduced mass and m_N is the
nuclear mass). Relativistic corrections to vacuum polarization of order alpha
(Zalpha)^4 mu are calculated, with a full account of the reduced-mass
dependence. The results shift theoretical predictions. The radiative-recoil
correction to vacuum polarization of order alpha (Z\alpha)^5 ln^2(Zalpha)
mu^2/m_N is obtained in leading logarithmic approximation. The results
emphasize the need for a unified treatment of relativistic corrections to
vacuum polarization in muonic hydrogen, muonic deuterium and muonic helium
ions, where the mass ratio of the orbiting particle to the nuclear mass is
larger than the fine-structure constant.Comment: 6 pages; RevTe
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