1,654 research outputs found
Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling
Nonstationary pump-probe interaction between short laser pulses propagating
in a resonant optically dense coherent medium is considered. A special
attention is paid to the case, where the density of two-level particles is high
enough that a considerable part of the energy of relatively weak external
laser-fields can be coherently absorbed and reemitted by the medium. Thus, the
field of medium reaction plays a key role in the interaction processes, which
leads to the collective behavior of an atomic ensemble in the strongly coupled
light-matter system. Such behavior results in the fast excitation interchanges
between the field and a medium in the form of the optical ringing, which is
analogous to polariton beating in the solid-state optics. This collective
oscillating response, which can be treated as successive beats between light
wave-packets of different group velocities, is shown to significantly affect
propagation and amplification of the probe field under its nonlinear
interaction with a nearly copropagating pump pulse. Depending on the probe-pump
time delay, the probe transmission spectra show the appearance of either
specific doublet or coherent dip. The widths of these features are determined
by the density-dependent field-matter coupling coefficient and increase during
the propagation. Besides that, the widths of the coherent features, which
appear close to the resonance in the broadband probe-spectrum, exceed the
absorption-line width, since, under the strong-coupling regime, the frequency
of the optical ringing exceeds the rate of incoherent relaxation. Contrary to
the stationary strong-field effects, the density- and coordinate-dependent
transmission spectra of the probe manifest the importance of the collective
oscillations and cannot be obtained in the framework of the single-atom model.Comment: 10 pages, 8 figures, to be published in Phys. Rev.
Disruption of the three-body gravitational systems: Lifetime statistics
We investigate statistics of the decay process in the equal-mass three-body
problem with randomized initial conditions. Contrary to earlier expectations of
similarity with "radioactive decay", the lifetime distributions obtained in our
numerical experiments turn out to be heavy-tailed, i.e. the tails are not
exponential, but algebraic. The computed power-law index for the differential
distribution is within the narrow range, approximately from -1.7 to -1.4,
depending on the virial coefficient. Possible applications of our results to
studies of the dynamics of triple stars known to be at the edge of disruption
are considered.Comment: 13 pages, 2 tables, 3 figure
Bargmann-Michel-Telegdi equation and one-particle relativistic approach
A reexamination of the semiclassical approach of the relativistic electron
indicates a possible variation of its helicity for electric and magnetic static
fields applied along its global motion due to zitterbewegung effects,
proportional to the anomalous part of the magnetic moment.Comment: 10 pages, LATEX2E, uses amsb
Multiple stars: Physics vs. dynamics
We review physical and dynamical parameters of multiple stars. Possible scenaria of multiple star formation are discussed: their birth in dense cloud cores and the decay of small stellar groups and clusters. We compare physical and dynamical features of simulated multiple stars formed by these processes with the actual multiple stars. Multiplicity function, their period, eccentricity and mass ratio distributions, hierarchy of the structures are analysed. Also we discuss multiple systems where the apparent ages of the components are different. Such diferences can be explained by poor evolutionary tracks for low-mass stars, by formation of such systems by capture or by merging of components during dynamical evolution of multiple stars. © 2008 Springer-Verlag Berlin Heidelberg
Dynamical stability of the quadruple systems HD 68255/6/7 and HD 76644
We analyze the dynamical stability of the hierarchical quadruple systems HD 68255/6/7 and HD 76644 via numerical integration of the equations of motion of the four-body problem, with a chainlike regularization of close stellar interactions. The observational errors were taken into account using Monte Carlo simulations, assuming that they possessed a Gaussian distribution. HD 68255/6/7 is probably stable, while HD 76644 is unstable with a probability exceeding 0.97 and with a disruption time of no more than 105 years. The influence of the observational errors and possible scenarios for the formation of unstable multiple stars are discussed. © Pleiades Publishing, Inc., 2006
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