24 research outputs found
Conservation laws for the Maxwell-Dirac equations with a dual Ohm's law
Using a general theorem on conservation laws for arbitrary differential
equations proved by Ibragimov, we have derived conservation laws for Dirac's
symmetrized Maxwell-Lorentz equations under the assumption that both the
electric and magnetic charges obey linear conductivity laws (dual Ohm's law).
We find that this linear system allows for conservation laws which are
non-local in time
Measurement of the spin of the M87 black hole from its observed twisted light
We present the first observational evidence that light propagating near a
rotating black hole is twisted in phase and carries orbital angular momentum
(OAM). This physical observable allows a direct measurement of the rotation of
the black hole. We extracted the OAM spectra from the radio intensity data
collected by the Event Horizon Telescope from around the black hole M87* by
using wavefront reconstruction and phase recovery techniques and from the
visibility amplitude and phase maps. This method is robust and complementary to
black-hole shadow circularity analyses. It shows that the M87* rotates
clockwise with an estimated rotation parameter with
confidence level (c.l.) and inclination , equivalent to
a magnetic arrested disk with inclination . From our
analysis we conclude, within a 6 c.l., that the M87* is rotating.Comment: Small addition on coherence. 5 pages, 2 figures Accepted for
publication in MNRAS Letter
Kerr spacetime geometric optics for vortex beams
We apply the analogy between gravitational fields and optical media in the
general relativistic geometric optics framework to describe how light can
acquire orbital angular momentum (OAM) when it traverses the gravitational
field of a massive rotating compact object and the interplay between OAM and
polarization. Kerr spacetimes are known not only to impose a gravitational
Faraday rotation on the polarization of a light beam, but also to set a
characteristic fingerprint in the orbital angular momentum distribution of the
radiation passing nearby a rotating black hole (BH). Kerr spacetime behaves
like an inhomogeneous and anisotropic medium, in which light can acquire
orbital angular momentum and spin-to-orbital angular momentum conversion can
occur, acting as a polarization and phase changing medium for the
gravitationally lensed light, as confirmed by the data analysis of M87* black
hole.Comment: 9 pages, 1 figur
Nonlinear physics of the ionosphere and LOIS/LOFAR
The ionosphere is the only large-scale plasma laboratory without walls that
we have direct access to. From results obtained in systematic, repeatable
experiments in this natural laboratory, where we can vary the stimulus and
observe its response in a controlled, repeatable manner, we can draw
conclusions on similar physical processes occurring naturally in the Earth's
plasma environment as well as in parts of the plasma universe that are not
easily accessible to direct probing.
Of particular interest is electromagnetic turbulence excited in the
ionosphere by beams of particles (photons, electrons) and its manifestation in
terms of secondary radiation (electrostatic and electromagnetic waves),
structure formation (solitons, cavitons, alfveons, striations), and the
associated exchange of energy, linear momentum, and angular momentum.
We present a new diagnostic technique, based on vector radio allowing the
utilization of EM angular momentum (vorticity), to study plasma turbulence
remotely.Comment: Six pages, two figures. To appear in Plasma Physics and Controlled
Fusio
Encoding many channels in the same frequency through radio vorticity: first experimental test
We have shown experimentally that it is possible to propagate and use the
properties of twisted non-monochromatic incoherent radio waves to
simultaneously transmit to infinity more radio channels on the same frequency
band by encoding them in different orbital angular momentum states. This novel
radio technique allows the implementation of, at least in principle, an
infinite number of channels on one and the same frequency, even without using
polarization or dense coding techniques. An optimal combination of all these
physical properties and techniques represents a solution for the problem of
radio band congestion. Our experimental findings show that the vorticity of
each twisted electromagnetic wave is preserved after the propagation, paving
the way for entirely new paradigms in radio communication protocols.Comment: 17 pages, 6 figures, with a public experiment, three audio files in
mp3 forma