66,008 research outputs found
Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings
We consider the gravitationally induced particle production from the quantum
vacuum which is defined by a free, massless and minimally coupled scalar field
during the formation of a gauge cosmic string. Previous discussions of this
topic estimate the power output per unit length along the string to be of the
order of ergs/sec/cm in the s-channel. We find that this production
may be completely suppressed. A similar result is also expected to hold for the
number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR
Quantum mechanics of a constrained electrically charged particle in the presence of electric currents
We discuss the dynamics of a classical spinless quantum particle carrying
electric charge and constrained to move on a non singular static surface in
ordinary three dimensional space in the presence of arbitrary configurations of
time independent electric currents. Starting from the canonical action in the
embedding space we show that a charged particle with charge couples to a
term linear in , where is the transverse component of the
electromagnetic vector potential and is the mean curvature in the surface.
This term cancels exactly a curvature contribution to the orbital magnetic
moment of the particle. It is shown that particles, independently of the value
of the charge, in addition to the known couplings to the geometry also couple
to the mean curvature in the surface when a Neumann type of constraint is
applied on the transverse fluctuations of the wave function. In contrast to a
Dirrichlet constraint on the transverse fluctuations a Neumann type of
constraint on these degrees of freedom will in general make the equations of
motion non separable. The exceptions are the equations of motion for
electrically neutral particles on surfaces with constant mean curvature. In the
presence of electric currents the equation of motion of a charged particle is
generally non separable independently of the coupling to the geometry and the
boundary constraints.Comment: to appear in Phys.Rev.
Ionization of Rydberg atoms in a low frequency field: modelling by maps of transition to chaotic behavior
We investigate a microwave ionization of highly excited atom in a low
frequency field and show that such a process may be studied on the bases of map
for the electron energy change during the period of the electron motion between
two subsequent passages at aphelion. Simple approximate criterion results to
the threshold field for transition to chaotic behavior very close to the
numerical results. We show that transition from adiabatic to chaotic ionization
mechanism takes place when the field frequency to the electron's Kepler
frequency ration approximately equals 0.1.Comment: 5 pages, LaTEX, 37Kb, 2 figures (compressed and uuencoded PostScript)
included in text. To be published in Chaos: The interplay between
stochastics, classics and quanta, Ed. by P. Garbaczewski, et al. Lecture
notes in Physics, 1995
A Preliminary Check-List of the Marine Algae of the Moss Landing Jetty: An Annotated Floristic Compilation. Annual Report, Part 7, 1973
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