20,880 research outputs found
The beryllium atom and beryllium positive ion in strong magnetic fields
The ground and a few excited states of the beryllium atom in external uniform
magnetic fields are calculated by means of our 2D mesh Hartree-Fock method for
field strengths ranging from zero up to 2.35*10^9T. With changing field
strength the ground state of the Be atom undergoes three transitions involving
four different electronic configurations which belong to three groups with
different spin projections S_z=0,-1,-2. For weak fields the ground state
configuration arises from the 1s^2 2s^2, S_z=0 configuration. With increasing
field strength the ground state evolves into the two S_z=-1 configurations
1s^22s 2p_{-1} and 1s^2 2p_{-1}3d_{-2}, followed by the fully spin polarised
S_z=-2 configuration 1s2p_{-1}3d_{-2}4f_{-3}. The latter configuration forms
the ground state of the beryllium atom in the high field regime \gamma>4.567.
The analogous calculations for the Be^+ ion provide the sequence of the three
following ground state configurations: 1s^22s and 1s^22p_{-1} (S_z=-1/2) and
1s2p_{-1}3d_{-2} (S_z=-3/2).Comment: 15 pages, 7 figure
Decay Constants and Semileptonic Form Factors of Pseudoscalar Mesons
A relativistic constituent quark model is adopted to give an unified
description of the leptonic and semileptonic decays of pseudoscalar mesons
(\pi, K, D, D_s, B, B_s). The calculated leptonic decay constants and form
factors are found to be in good agreement with available experimental data and
the results of other approaches. Eventually, the model is found to reproduce
the scaling behaviours of spin-flavor symmetry in the heavy-quark limit.Comment: 5 pages LaTeX; based on talk given at the "QFTHEP '99 Workshop",
Moscow, May 27- June 2, 199
A model of gravitation with global U(1)-symmetry
It is shown that an embedding of the general relativity space into a flat
space gives a model of gravitation with the global symmetry and the
discrete one. The last one may be transformed into the symmetry
of the unified model, and the demand of independence of and
transformations leads to the estimate where
is an analog of the Weinberg angle of the standard model.Comment: 7 page
Relativistic cross sections of mass stripping and tidal disruption of a star by a super-massive rotating black hole
[abbreviated] We consider the problem of tidal disruption of a star by a
super-massive Kerr black hole. Using a numerically fast Lagrangian model of the
tidally disrupted star we survey the parameter space of the problem and find
the regions in the parameter space where the total disruption of the star or a
partial mass loss take place as a result of fly-by around the black hole. Our
treatment is based on General Relativity, and we consider the range of the
black hole masses where the tidal disruption competes with the relativistic
effect of direct capture of the star by the black hole. We find that our
results can be represented on the plane of specific orbital angular momenta of
the star . We calculate the contours of a given mass
loss of the star on this plane, referred to as the tidal cross sections, for a
given black hole mass , rotational parameter and inclination of the
trajectory of the star with respect to the black hole equatorial plane. It is
shown that the tidal cross sections can be approximated as circles symmetric
above the axis , and shifted with respect to the origin of the
coordinates in direction of negative . The radii and shifts of
these circles are obtained numerically for the black hole masses in the range
and different values of . It is
shown that when the tidal disruption takes place for and when the tidal disruption is possible for .Comment: 11 pages, 16 figures, A&A in press, the text is clarified, the title
and the abstract shown in text are change
Light Curve Solutions of Eclipsing Binaries in SMC
We propose a procedure for light-curve solution of eclipsing binary stars in
the Small Magellanic Cloud for which photometric data have been obtained in the
framework of the OGLE project as well as way of determination of the global
stellar parameters on the basis of the obtained solutions, some empirical
relations as well as the distance to the SMC. Several examples illustrate this
procedure.Comment: 10 pages, 2 figures, accepte
The semileptonic form factors of B and D mesons in the Quark Confinement Model
The form factors of the weak currents, which appear in the semileptonic
decays of the heavy pseudoscalar mesons, are calculated within the quark
confinement model by taking into account, for the first time, the structure of
heavy meson vertex and the finite quark mass contribution in the heavy quark
propagators. The results are in quite good agreement with the experimental
data.Comment: 12 pages LaTeX (elsart.sty) + 3 figure
Exchange and correlation energies of ground states of atoms and molecules in strong magnetic fields
Using a Hartree-Fock mesh method and a configuration interaction approach
based on a generalized Gaussian basis set we investigate the behaviour of the
exchange and correlation energies of small atoms and molecules, namely th e
helium and lithium atom as well as the hydrogen molecule, in the presence of a
magnetic field covering the regime B=0-100a.u. In general the importance of the
exchange energy to the binding properties of at oms or molecules increases
strongly with increasing field strength. This is due to the spin-flip
transitions and in particular due to the contributions of the tightly bound
hydrogenic state s which are involved in the corresponding ground states of
different symmetries. In contrast to the exchange energy the correlation energy
becomes less relevant with increasing field strength. This holds for the
individual configurations constituting the ground state and for the crossovers
of the global ground state.Comment: 4 Figures acc.f.publ.in Phys.Rev.
Correlations of the local density of states in quasi-one-dimensional wires
We report a calculation of the correlation function of the local density of
states in a disordered quasi-one-dimensional wire in the unitary symmetry class
at a small energy difference. Using an expression from the supersymmetric
sigma-model, we obtain the full dependence of the two-point correlation
function on the distance between the points. In the limit of zero energy
difference, our calculation reproduces the statistics of a single localized
wave function. At logarithmically large distances of the order of the Mott
scale, we obtain a reentrant behavior similar to that in strictly
one-dimensional chains.Comment: Published version. Minor technical and notational improvements. 16
pages, 1 figur
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