7,179 research outputs found
Black hole superradiance and polarization-dependent bending of light
An inhomogeneous pseudo-scalar field configuration behaves like an optically
active medium. Consequently, if a light ray passes through an axion cloud
surrounding a Kerr black hole, it may experience a polarization-dependent
bending. We explore the size and relevance of such effect considering both the
QCD axion and a generic axion-like particle.Comment: Bulk of 29 pages + 11 figures. v2: minor changes, version accepted
for publication in JCA
Asymptotic Inverse Problem for Almost-Periodically Perturbed Quantum Harmonic Oscillator
Consider quantum harmonic oscillator, perturbed by an even almost-periodic
complex-valued potential with bounded derivative and primitive. Suppose that we
know the first correction to the spectral asymptotics
(, where
and is the spectrum of the unperturbed and the perturbed
operators, respectively). We obtain the formula that recovers the frequencies
and the Fourier coefficients of the perturbation.Comment: 6 page
Covariant un-reduction for curve matching
The process of un-reduction, a sort of reversal of reduction by the Lie group
symmetries of a variational problem, is explored in the setting of field
theories. This process is applied to the problem of curve matching in the
plane, when the curves depend on more than one independent variable. This
situation occurs in a variety of instances such as matching of surfaces or
comparison of evolution between species. A discussion of the appropriate
Lagrangian involved in the variational principle is given, as well as some
initial numerical investigations.Comment: Conference paper for MFCA201
Mode-balancing far field control of light localization in nanoantennas
Light localization is controlled at a scale of lambda/10 in the harmonic
regime from the far field domain in a plasmonic nanoantenna. The nanoantenna
under study consists of 3 aligned spheres 50 nm in diameter separated by a
distance of 5 nm. By simply tuning the orientation of an incident plane wave,
symmetric and antisymmetric mode-balancing induces a strong enhancement of the
near field intensity in one cavity while nullifying the light intensity in the
other cavity. Furthermore, it is demonstrated that the dipolar moment of a
plasmonic particle can be fully extinguished when strongly coupled with a dimer
of identical nanoparticles. Consequently, optical transparency can be achieved
in an ultra-compact symmetric metallic structure
Ruelle-Pollicott Resonances of Stochastic Systems in Reduced State Space. Part II: Stochastic Hopf Bifurcation
The spectrum of the generator (Kolmogorov operator) of a diffusion process,
referred to as the Ruelle-Pollicott (RP) spectrum, provides a detailed
characterization of correlation functions and power spectra of stochastic
systems via decomposition formulas in terms of RP resonances. Stochastic
analysis techniques relying on the theory of Markov semigroups for the study of
the RP spectrum and a rigorous reduction method is presented in Part I. This
framework is here applied to study a stochastic Hopf bifurcation in view of
characterizing the statistical properties of nonlinear oscillators perturbed by
noise, depending on their stability. In light of the H\"ormander theorem, it is
first shown that the geometry of the unperturbed limit cycle, in particular its
isochrons, is essential to understand the effect of noise and the phenomenon of
phase diffusion. In addition, it is shown that the spectrum has a spectral gap,
even at the bifurcation point, and that correlations decay exponentially fast.
Explicit small-noise expansions of the RP eigenvalues and eigenfunctions are
then obtained, away from the bifurcation point, based on the knowledge of the
linearized deterministic dynamics and the characteristics of the noise. These
formulas allow one to understand how the interaction of the noise with the
deterministic dynamics affect the decay of correlations. Numerical results
complement the study of the RP spectrum at the bifurcation, revealing useful
scaling laws. The analysis of the Markov semigroup for stochastic bifurcations
is thus promising in providing a complementary approach to the more geometric
random dynamical system approach. This approach is not limited to
low-dimensional systems and the reduction method presented in part I is applied
to a stochastic model relevant to climate dynamics in part III
Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies
The classical dynamical model for reactions induced by weakly-bound nuclei at
near-barrier energies is developed further. It allows a quantitative study of
the role and importance of incomplete fusion dynamics in asymptotic
observables, such as the population of high-spin states in reaction products as
well as the angular distribution of direct alpha-production. Model calculations
indicate that incomplete fusion is an effective mechanism for populating
high-spin states, and its contribution to the direct alpha production yield
diminishes with decreasing energy towards the Coulomb barrier. It also becomes
notably separated in angles from the contribution of no-capture breakup events.
This should facilitate the experimental disentanglement of these competing
reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the
author), Accepted in Journal of Physics
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