142 research outputs found
Spontaneous spherical symmetry breaking in atomic confinement
The effect of spontaneous breaking of initial SO(3) symmetry is shown to be
possible for an H-like atom in the ground state, when it is confined in a
spherical box under general boundary conditions of "not going out" through the
box surface (i.e. third kind or Robin's ones), for a wide range of physically
reasonable values of system parameters. The reason is that such boundary
conditions could yield a large magnitude of electronic wavefunction in some
sector of the box boundary, what in turn promotes atomic displacement from the
box center towards this part of the boundary, and so the underlying SO(3)
symmetry spontaneously breaks. The emerging Goldstone modes, coinciding with
rotations around the box center, restore the symmetry by spreading the atom
over a spherical shell localized at some distances from the box center. Atomic
confinement inside the cavity proceeds dynamically -- due to the boundary
condition the deformation of electronic wavefunction near the boundary works as
a spring, that returns the atomic nuclei back into the box volume.Comment: 12 pages, 12 figures. arXiv admin note: text overlap with
arXiv:1301.3399 . authors note: added reference, changes in introduction,
added acknowledgemen
Comparative study of semiclassical approaches to quantum dynamics
Quantum states can be described equivalently by density matrices, Wigner
functions or quantum tomograms. We analyze the accuracy and performance of
three related semiclassical approaches to quantum dynamics, in particular with
respect to their numerical implementation. As test cases, we consider the time
evolution of Gaussian wave packets in different one-dimensional geometries,
whereby tunneling, resonance and anharmonicity effects are taken into account.
The results and methods are benchmarked against an exact quantum mechanical
treatment of the system, which is based on a highly efficient Chebyshev
expansion technique of the time evolution operator.Comment: 32 pages, 8 figures, corrected typos and added references; version as
publishe
Investigation of the Chaotic Dynamics of an Electron Beam with a Virtual Cathode in an External Magnetic Field
The effect of the strength of the focusing magnetic field on chaotic dynamic
processes occurring inan electron beam with a virtual cathode, as well as on
the processes whereby the structures form in the beamand interact with each
other, is studied by means of two-dimensional numerical simulations based on
solving a self-consistent set of Vlasov-Maxwell equations. It is shown that, as
the focusing magnetic field is decreased,the dynamics of an electron beam with
a virtual cathode becomes more complicated due to the formation andinteraction
of spatio-temporal longitudinal and transverse structures in the interaction
region of a vircator. The optimum efficiency of the interaction of an electron
beam with the electromagnetic field of the vircator isachieved at a
comparatively weak external magnetic field and is determined by the
fundamentally two-dimensional nature of the motion of the beam electrons near
the virtual cathode.Comment: 12 pages, 8 figure
Dijet Event Shapes as Diagnostic Tools
Event shapes have long been used to extract information about hadronic final
states and the properties of QCD, such as particle spin and the running
coupling. Recently, a family of event shapes, the angularities, has been
introduced that depends on a continuous parameter. This additional
parameter-dependence further extends the versatility of event shapes. It
provides a handle on nonperturbative power corrections, on non-global
logarithms, and on the flow of color in the final state.Comment: 18 pages, 3 figure
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