320 research outputs found
New solutions of relativistic wave equations in magnetic fields and longitudinal fields
We demonstrate how one can describe explicitly the present arbitrariness in
solutions of relativistic wave equations in external electromagnetic fields of
special form. This arbitrariness is connected to the existence of a
transformation, which reduces effectively the number of variables in the
initial equations. Then we use the corresponding representations to construct
new sets of exact solutions, which may have a physical interest. Namely, we
present new sets of stationary and nonstationary solutions in magnetic field
and in some superpositions of electric and magnetic fields.Comment: 25 pages, LaTex fil
Quantum motion in superposition of Aharonov-Bohm with some additional electromagnetic fields
The structure of additional electromagnetic fields to the Aharonov-Bohm
field, for which the Schr\"odinger, Klein-Gordon, and Dirac equations can be
solved exactly are described and the corresponding exact solutions are found.
It is demonstrated that aside from the known cases (a constant and uniform
magnetic field that is parallel to the Aharonov-Bohm solenoid, a static
spherically symmetrical electric field, and the field of a magnetic monopole),
there are broad classes of additional fields. Among these new additional fields
we have physically interesting electric fields acting during a finite time, or
localized in a restricted region of space. There are additional time-dependent
uniform and isotropic electric fields that allow exact solutions of the
Schrodinger equation. In the relativistic case there are additional electric
fields propagating along the Aharonov-Bohm solenoid with arbitrary electric
pulse shape
Coherent and semiclassical states in magnetic field in the presence of the Aharonov-Bohm solenoid
A new approach to constructing coherent states (CS) and semiclassical states
(SS) in magnetic-solenoid field is proposed. The main idea is based on the fact
that the AB solenoid breaks the translational symmetry in the xy-plane, this
has a topological effect such that there appear two types of trajectories which
embrace and do not embrace the solenoid. Due to this fact, one has to construct
two different kinds of CS/SS, which correspond to such trajectories in the
semiclassical limit. Following this idea, we construct CS in two steps, first
the instantaneous CS (ICS) and the time dependent CS/SS as an evolution of the
ICS. The construction is realized for nonrelativistic and relativistic spinning
particles both in (2+1)- and (3+1)- dimensions and gives a non-trivial example
of SS/CS for systems with a nonquadratic Hamiltonian. It is stressed that CS
depending on their parameters (quantum numbers) describe both pure quantum and
semiclassical states. An analysis is represented that classifies parameters of
the CS in such respect. Such a classification is used for the semiclassical
decompositions of various physical quantities.Comment: 35 pages, 2 figures. Some typos in (77), (101), and (135) corrected
with respect to the published version. Results unchange
Effective spectrum width of the synchrotron radiation
For an exact quantitative description of spectral properties of synchrotron
radiation (SR), the concept of effective width of the spectrum is introduced.
In the most interesting case, which corresponds to the ultrarelativistic limit
of SR, the effective width of the spectrum is calculated for the polarization
components, and new physically important quantitative information on the
structure of spectral distributions is obtained. For the first time, the
spectral distribution for the circular polarization component of the SR for the
upper half-space is obtained within classical theory
Dependence of effective spectrum width of synchrotron radiation on particle energy
For an exact quantitative description of spectral properties in the theory of
synchrotron radiation, the concept of effective spectral width is introduced.
In the classical theory, numeric calculations of effective spectral width
(using an effective width not exceeding 100 harmonics) for polarization
components of synchrotron radiation are carried out. The dependence of the
effective spectral width and initial harmonic on the energy of a radiating
particle is established
Aspects of Two-Level Systems under External Time Dependent Fields
The dynamics of two-level systems in time-dependent backgrounds is under
consideration. We present some new exact solutions in special backgrounds
decaying in time. On the other hand, following ideas of Feynman, Vernon and
Hellwarth, we discuss in detail the possibility to reduce the quantum dynamics
to a classical Hamiltonian system. This, in particular, opens the possibility
to directly apply powerful methods of classical mechanics (e.g. KAM methods) to
study the quantum system. Following such an approach, we draw conclusions of
relevance for ``quantum chaos'' when the external background is periodic or
quasi-periodic in time.Comment: To appear in J. Phys. A. Mathematical and Genera
Charged particles in crossed and longitudinal electromagnetic fields and beam guides
We consider a class of electromagnetic fields that contains crossed fields
combined with longitudinal electric and magnetic fields. We study the motion of
a classical particle (solutions of the Lorentz equations) in such fields. Then,
we present an analysis that allows one to decide which fields from the class
act as a beam guide for charged particles, and we find some time-independent
and time-dependent configurations with beam guiding properties. We demonstrate
that the Klein-Gordon and Dirac equations with all the fields from the class
can be solved exactly. We study these solutions, which were not known before,
and prove that they form complete and orthogonal sets of functions.Comment: 14 page
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