49,638 research outputs found
Dynamics of two-photon paired superradiance
We develop for dipole-forbidden transition a dynamical theory of two-photon
paired superradiance, or PSR for short. This is a cooperative process
characterized by two photons back to back emitted with equal energies. By
irradiation of trigger laser from two target ends, with its frequency tuned at
the half energy between two levels, a macroscopically coherent state of medium
and fields dynamically emerges as time evolves and large signal of amplified
output occurs with a time delay. The basic semi-classical equations in 1+1
spacetime dimensions are derived for the field plus medium system to describe
the spacetime evolution of the entire system, and numerically solved to
demonstrate existence of both explosive and weak PSR phenomena in the presence
of relaxation terms. The explosive PSR event terminates accompanying a sudden
release of most energy stored in the target. Our numerical simulations are
performed using a vibrational transition of
para-H molecule, and taking many different excited atom number densities
and different initial coherences between the metastable and the ground states.
In an example of number density close to cm and of high
initial coherence, the explosive event terminates at several nano seconds after
the trigger irradiation, when the phase relaxation time of ns is
taken. After PSR events the system is expected to follow a steady state
solution which is obtained by analytic means, and is made of many objects of
field condensates endowed with a topological stability.Comment: 31 pages, 15 figures. Revised for publication. Title slightly
changed, detailed explanation added, minor typos corrected. All equations and
figures unchange
Contracted Representation of Yang's Space-Time Algebra and Buniy-Hsu-Zee's Discrete Space-Time
Motivated by the recent proposition by Buniy, Hsu and Zee with respect to
discrete space-time and finite spatial degrees of freedom of our physical world
with a short- and a long-distance scales, and we reconsider the
Lorentz-covariant Yang's quantized space-time algebra (YSTA), which is
intrinsically equipped with such two kinds of scale parameters, and
. In accordance with their proposition, we find the so-called contracted
representation of YSTA with finite spatial degrees of freedom associated with
the ratio , which gives a possibility of the divergence-free
noncommutative field theory on YSTA. The canonical commutation relations
familiar in the ordinary quantum mechanics appear as the cooperative
Inonu-Wigner's contraction limit of YSTA, and $R \to \infty.
Uniaxial pressure dependencies of the phase boundary of TlCuCl_3
We present a thermal expansion and magnetostriction study of TlCuCl_3, which
shows a magnetic-field induced transition from a spin gap phase to a Neel
ordered phase. Using Ehrenfest relations we derive huge and strongly
anisotropic uniaxial pressure dependencies of the respective phase boundary,
e.g. the transition field changes by about GPa depending on the
direction of uniaxial pressure.Comment: 2 pages, e figures; presented at SCES200
Critical exponents of Nikolaevskii turbulence
We study the spatial power spectra of Nikolaevskii turbulence in
one-dimensional space. First, we show that the energy distribution in
wavenumber space is extensive in nature. Then, we demonstrate that, when
varying a particular parameter, the spectrum becomes qualitatively
indistinguishable from that of Kuramoto-Sivashinsky turbulence. Next, we derive
the critical exponents of turbulent fluctuations. Finally, we argue that in
some previous studies, parameter values for which this type of turbulence does
not appear were mistakenly considered, and we resolve inconsistencies obtained
in previous studies.Comment: 9 pages, 6 figure
Massless Scalar Field Propagator in a Quantized Space-Time
We consider in detail the analytic behaviour of the non-interacting massless
scalar field two-point function in H.S. Snyder's discretized non-commuting
spacetime. The propagator we find is purely real on the Euclidean side of the
complex plane and goes like as from either the
Euclidean or Minkowski side. The real part of the propagator goes smoothly to
zero as increases to the discretization scale and remains zero
for . This behaviour is consistent with the termination of
single-particle propagation on the ultraviolet side of the discretization
scale. The imaginary part of the propagator, consistent with a
multiparticle-production branch discontinuity, is finite and continuous on the
Minkowski side, slowly falling to zero when . Finally, we
argue that the spectral function for the multiparticle states appears to
saturate as probes just beyond the discretization scale. We
speculate on the cosmological consequences of such a spectral function.Comment: 6 pages, 1 eps figure embedded in manuscrip
On the magnon interaction in Haematite. 2: Magnon energy of the acoustical mode and magnetic critical fields
Previous spin wave theories of the antiferromagnet hematite were extended. The behavior of thermodynamic quantities around the Morin transition temperature was studied, and the latent heat of the Morin transition was calculated. The temperature dependence of the antiferromagnetic resonance frequency and the parallel and perpendicular critical spin-flop magnetic fields were calculated. It was found that the theory agrees well with experiment
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