4,976 research outputs found
Chiral Skyrmionic matter in non-centrosymmetric magnets
Axisymmetric magnetic strings with a fixed sense of rotation and nanometer
sizes (chiral magnetic vortices or Skyrmions) have been predicted to exist in a
large group of non-centrosymmetric crystals more than two decades ago. Recently
these extraordinary magnetic states have been directly observed in thin layers
of cubic helimagnet (Fe,Co)Si. In this report we apply our earlier theoretical
findings to review main properties of chiral Skyrmions, to elucidate their
physical nature, and to analyse these recent experimental results on
magnetic-field-driven evolution of Skyrmions and helicoids in chiral
helimagnets.Comment: 13 pages, 7 figures, invited talk - JEMS-2010 ( 23-28 August, Krakow,
Poland
Solutions for real dispersionless Veselov-Novikov hierarchy
We investigate the dispersionless Veselov-Novikov (dVN) equation based on the
framework of dispersionless two-component BKP hierarchy. Symmetry constraints
for real dVN system are considered. It is shown that under symmetry reductions,
the conserved densities are therefore related to the associated Faber
polynomials and can be solved recursively. Moreover, the method of hodograph
transformation as well as the expressions of Faber polynomials are used to find
exact real solutions of the dVN hierarchy.Comment: 14 page
Probability of radiation of twisted photons by classical currents
The general formula for the probability of radiation of a twisted photon by a
classical current is derived. The general theory of generation of twisted
photons by undulators is developed. It is proved that the probability to record
a twisted photon produced by a classical current is equal to the average number
of twisted photons in a given state. The general formula for the projection of
the total angular momentum of twisted photons with given the energy, the
longitudinal projection of momentum, and the helicity is obtained. The symmetry
property of the average number of twisted photons produced by a charged
particle moving along a planar trajectory is found. The explicit formulas for
the average number of twisted photons generated by undulators both in the
dipole and wiggler regimes are obtained. It is established that, for the
forward radiation of an ideal right-handed helical undulator, the harmonic
number of the twisted photon coincides with its projection of the total
angular momentum . As for the ideal left-handed helical undulator, we obtain
that . It is found that the forward radiation of twisted photons by a
planar undulator obeys the selection rule that is an even number. It
turns out that the average number of twisted photons produced by the undulator
and detected off the undulator axis is a periodic function of in a certain
spectral band of the quantum numbers .Comment: 36 pp; some misprints corrected; formulas (48)-(51) change
Properties of an ultrarelativistic charged particle radiation in a constant homogeneous crossed electromagnetic field
The properties of radiation created by a classical ultrarelativistic scalar
charged particle in a constant homogeneous crossed electromagnetic field are
described both analytically and numerically with radiation reaction taken into
account in the form of the Landau-Lifshitz equation. The total radiation
naturally falls into two parts: the radiation formed at the entrance point of a
particle into the crossed field (the synchrotron entrance radiation), and the
radiation coming from the late-time asymptotics of a particle motion (the
de-excited radiation). The synchrotron entrance radiation resembles, although
does not coincide with, the ultrarelativistic limit of the synchrotron
radiation: its distribution over energies and angles possesses almost the same
properties. The de-excited radiation is soft, not concentrated in the plane of
motion of a charged particle, and almost completely circularly polarized. The
photon energy delivering the maximum to its spectral angular distribution
decreases with increasing the initial energy of a charged particle, while the
maximum value of this distribution remains the same at the fixed observation
angle. The ultraviolet and infrared asymptotics of the total radiation are also
described.Comment: 14 pp, 3 fig
On the heavenly equation hierarchy and its reductions
Second heavenly equation hierarchy is considered using the framework of
hyper-K\"ahler hierarchy developed by Takasaki. Generating equations for the
hierarchy are introduced, they are used to construct generating equations for
reduced hierarchies. General -reductions, logarithmic reduction and rational
reduction for one of the Lax-Sato functions are discussed. It is demonstrated
that rational reduction is equivalent to the symmetry constraint.Comment: 13 pages, LaTeX, minor misprints corrected, references adde
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