18,197 research outputs found
Spatio-temporal vortex beams and angular momentum
We present a space-time generalization of the known spatial (monochromatic)
wave vortex beams carrying intrinsic orbital angular momentum (OAM) along the
propagation direction. Generic spatio-temporal vortex beams are polychromatic
and can carry intrinsic OAM at an arbitrary angle to the mean momentum.
Applying either (i) a transverse wave-vector shift or (ii) a Lorentz boost to a
monochromatic Bessel beam, we construct a family of either (i) time-diffracting
or (ii) non-diffracting spatio-temporal Bessel beams, which are exact solutions
of the Klein-Gordon wave equations. The proposed spatio-temporal OAM states are
able to describe either photon or electron vortex states (both relativistic and
nonrelativistic), and can find applications in particle collisions, optics of
moving media, quantum communications, and astrophysics.Comment: 9 pages, 6 figures, to appear in Phys. Rev.
Reissner-Nordstrom black hole lensing
In this paper we study the strong gravitational lensing scenario where the
lens is a Reissner-Nordstrom black hole. We obtain the basic equations and show
that, as in the case of Schwarzschild black hole, besides the primary and
secondary images, two infinite sets of relativistic images are formed. We find
analytical expressions for the positions and amplifications of the relativistic
images. The formalism is applied to the case of a low-mass black hole placed at
the galactic halo.Comment: 16 pages, 5 figure
Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole
We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.Comment: 19 pages, 4 figures
Tensor mass and particle number peak at the same location in the scalar-tensor gravity boson star models - an analytical proof
Recently in boson star models in framework of Brans-Dicke theory, three
possible definitions of mass have been identified, all identical in general
relativity, but different in scalar-tensor theories of gravity.It has been
conjectured that it's the tensor mass which peaks, as a function of the central
density, at the same location where the particle number takes its maximum.This
is a very important property which is crucial for stability analysis via
catastrophe theory. This conjecture has received some numerical support. Here
we give an analytical proof of the conjecture in framework of the generalized
scalar-tensor theory of gravity, confirming in this way the numerical
calculations.Comment: 9 pages, latex, no figers, some typos corrected, reference adde
Extended Weyl Calculus and Application to the Phase-Space Schr\"{o}dinger Equation
We show that the Schr\"{o}dinger equation in phase space proposed by
Torres-Vega and Frederick is canonical in the sense that it is a natural
consequence of the extended Weyl calculus obtained by letting the Heisenberg
group act on functions (or half-densities) defined on phase space. This allows
us, in passing, to solve rigorously the TF equation for all quadratic
Hamiltonians.Comment: To appear in J. Phys. A: Math. and genera
Temperature-driven single-valley Dirac fermions in HgTe quantum wells
We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe
quantum wells below and above the critical well thickness . Our results,
obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K,
clearly indicate a change of the band-gap energy with temperature. The quantum
well wider than evidences a temperature-driven transition from
topological insulator to semiconductor phases. At the critical temperature of
90 K, the merging of inter- and intra-band transitions in weak magnetic fields
clearly specifies the formation of gapless state, revealing the appearance of
single-valley massless Dirac fermions with velocity of
ms. For both quantum wells, the energies extracted from
experimental data are in good agreement with calculations on the basis of the
8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages
Magnetars in the Metagalaxy: An Origin for Ultra High Energy Cosmic Rays in the Nearby Universe
I show that the relativistic winds of newly born magnetars with khz initial
spin rates, occurring in all normal galaxies, can accelerate ultrarelativistic
light ions with an E^{-1} injection spectrum, steepening to E^{-2} at higher
energies, with an upper cutoff above 10^{21} eV. Interactions with the CMB
yield a spectrum in good accord with the observed spectrum of Ultra-High Energy
Cosmic Rays (UHECR), if ~ 5-10% of the magnetars are born with voltages
sufficiently high to accelerate the UHECR. The form the spectrum spectrum takes
depends on the gravitational wave losses during the magnetars' early spindown -
pure electromagnetic spindown yields a flattening of the E^3 J(E) spectrum
below 10^{20} eV, while a moderate GZK ``cutoff'' appears if gravitational wave
losses are strong enough. I outline the physics such that the high energy
particles escape with small energy losses from a magnetar's natal supernova,
including Rayleigh-Taylor ``shredding'' of the supernova envelope, expansion of
a relativistic blast wave into the interstellar medium, acceleration of the UHE
ions through surf-riding in the electromgnetic fields of the wind, and escape
of the UHE ions in the rotational equator with negligible radiation loss. The
abundance of interstellar supershells and unusually large supernova remnants
suggests that most of the initial spindown energy is radiated in khz
gravitational waves for several hours after each supernova, with effective
strains from sources at typical distances ~ 3 x 10^{-21}. Such bursts of
gravitational radiation should correlate with bursts of ultra-high energy
particles. The Auger experiment should see such bursts every few years.Comment: 49 pages, 2 Figures, LaTeX (aastex, epsfig, graphicx, float), to be
published June 1, 2003 in the ApJ. Corrected discussion of electromagnetic
surf-riding as the acceleration mechanism and more typos, and reference
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