78 research outputs found
On the harmonic oscillator on the Lobachevsky plane
We introduce the harmonic oscillator on the Lobachevsky plane with the aid of
the potential where is the curvature
radius and is the geodesic distance from a fixed center. Thus the potential
is rotationally symmetric and unbounded likewise as in the Euclidean case. The
eigenvalue equation leads to the differential equation of spheroidal functions.
We provide a basic numerical analysis of eigenvalues and eigenfunctions in the
case when the value of the angular momentum, , equals 0.Comment: to appear in Russian Journal of Mathematical Physics (memorial volume
in honor of Vladimir Geyler
Linked and knotted beams of light, conservation of helicity and the flow of null electromagnetic fields
Maxwell's equations allow for some remarkable solutions consisting of pulsed
beams of light which have linked and knotted field lines. The preservation of
the topological structure of the field lines in these solutions has previously
been ascribed to the fact that the electric and magnetic helicity, a measure of
the degree of linking and knotting between field lines, are conserved. Here we
show that the elegant evolution of the field is due to the stricter condition
that the electric and magnetic fields be everywhere orthogonal. The field lines
then satisfy a `frozen field' condition and evolve as if they were unbreakable
filaments embedded in a fluid. The preservation of the orthogonality of the
electric and magnetic field lines is guaranteed for null, shear-free fields
such as the ones considered here by a theorem of Robinson. We calculate the
flow field of a particular solution and find it to have the form of a Hopf
fibration moving at the speed of light in a direction opposite to the
propagation of the pulsed light beam, a familiar structure in this type of
solution. The difference between smooth evolution of individual field lines and
conservation of electric and magnetic helicity is illustrated by considering a
further example in which the helicities are conserved, but the field lines are
not everywhere orthogonal. The field line configuration at time t=0 corresponds
to a nested family of torus knots but unravels upon evolution
Unusual formations of the free electromagnetic field in vacuum
It is shown that there are exact solutions of the free Maxwell equations
(FME) in vacuum allowing an existence of stable spherical formations of the
free magnetic field and ring-like formations of the free electric field. It is
detected that a form of these spheres and rings does not change with time in
vacuum. It is shown that these convergent solutions are the result of an
interference of some divergent solutions of FME. One can surmise that these
electromagnetic formations correspond to Kapitsa's hypothesis about
interference origin and a structure of fireball.Comment: Revtex-file, without figures. To get lournal-pdf-copy with figures
contact with [email protected]
The dynamical nature of time
It is usually assumed that the "" parameter in the equations of dynamics
can be identified with the indication of the pointer of a clock. Things are not
so easy, however. In fact, since the equations of motion can be written in
terms of but also of , being any well behaved function, each
one of those infinite parametric times is as good as the Newtonian one to
study classical dynamics. Here we show that the relation between the
mathematical parametric time in the equations of dynamics and the physical
dynamical time that is measured with clocks is more complex and subtle
than usually assumed. These two times, therefore, must be carefully
distinguished since their difference may have significant consequences.
Furthermore, we show that not all the dynamical clock-times are necessarily
equivalent and that the observational fingerprint of this non-equivalence has
the same form as that of the Pioneer anomaly.Comment: 13 pages, no figure
Hamiltonians separable in cartesian coordinates and third-order integrals of motion
We present in this article all Hamiltonian systems in E(2) that are separable
in cartesian coordinates and that admit a third-order integral, both in quantum
and in classical mechanics. Many of these superintegrable systems are new, and
it is seen that there exists a relation between quantum superintegrable
potentials, invariant solutions of the Korteweg-De Vries equation and the
Painlev\'e transcendents.Comment: 19 pages, Will be published in J. Math. Phy
General structure of the solutions of the Hamiltonian constraints of gravity
A general framework for the solutions of the constraints of pure gravity is
constructed. It provides with well defined mathematical criteria to classify
their solutions in four classes. Complete families of solutions are obtained in
some cases. A starting point for the systematic study of the solutions of
Einstein gravity is suggested.Comment: 17 pages, LaTeX, submitted to International J. of Geom. Meth. in
Modern Physics. Added comments in the last sectio
The Pioneer riddle, the quantum vacuum and the variation of the light velocity
It is shown that the same phenomenological Newtonian model recently proposed, which accounts for the cosmological evolution of the fine-structure constant, suggests furthermore an explanation of the unmodelled acceleration a(P) similar or equal to 8.5 x 10(-10) m/s(2) of the Pioneer 10/11 spaceships reported by Anderson et al. in 1998. In the view presented here, the permittivity and permeability of the empty space are decreasing adiabatically, and the light is accelerating therefore, as a consequence of the progressive attenuation of the quantum vacuum due to the combined effect of its gravitational interaction with all the expanding universe and the fourth Heisenberg relation. It is argued that the spaceships might not have any extra acceleration (but would follow instead the unchanged Newton laws), the observed effect being due to an adiabatic acceleration of the light equal to a(P), which has the same observational radio signature as the anomalous acceleration of the Pioneers
Lie systems and integrability conditions for t-dependent frequency harmonic oscillators
Time-dependent frequency harmonic oscillators (TDFHO's) are studied through
the theory of Lie systems. We show that they are related to a certain kind of
equations in the Lie group SL(2,R). Some integrability conditions appear as
conditions to be able to transform such equations into simpler ones in a very
specific way. As a particular application of our results we find t-dependent
constants of the motion for certain one-dimensional TDFHO's. Our approach
provides an unifying framework which allows us to apply our developments to all
Lie systems associated with equations in SL(2,R) and to generalise our methods
to study any Lie system
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