3,424 research outputs found
Solving the characteristic initial value problem for colliding plane gravitational and electromagnetic waves
A method is presented for solving the characteristic initial value problem
for the collision and subsequent nonlinear interaction of plane gravitational
or gravitational and electromagnetic waves in a Minkowski background. This
method generalizes the monodromy transform approach to fields with nonanalytic
behaviour on the characteristics inherent to waves with distinct wave fronts.
The crux of the method is in a reformulation of the main nonlinear symmetry
reduced field equations as linear integral equations whose solutions are
determined by generalized (``dynamical'') monodromy data which evolve from data
specified on the initial characteristics (the wavefronts).Comment: 4 pages, RevTe
D-branes and orientifolds of SO(3)
We study branes and orientifolds on the group manifold of SO(3). We consider
particularly the case of the equatorial branes, which are projective planes. We
show that a Dirac-Born-Infeld action can be defined on them, although they are
not orientable. We find that there are two orientifold projections with the
same spacetime action, which differ by their action on equatorial branes.Comment: 11 pages, no figure, uses JHEP3.cls. V2 : minor correction
Dynamic spin-charge coupling: spin Hall magnetoresistance in non-magnetic conductors
The dynamic coupling between spin and charge currents in non-magnetic
conductors is considered. As a consequence of this coupling, the spin dynamics
is directly reflected in the electrical impedance of the sample, with a
relevant frequency scale defined by spin relaxation and spin diffusion. This
allows the observation of the electron spin resonance by purely electrical
measurements.Comment: Submitted to Phys. Rev. Lett. on 18/12/201
Nonperturbative Contributions in an Analytic Running Coupling of QCD
In the framework of analytic approach to QCD the nonperturbative
contributions in running coupling of strong interaction up to 4-loop order are
obtained in an explicit form. For all they are shown to be
represented in the form of an expansion in inverse powers of Euclidean momentum
squared. The expansion coefficients are calculated for different numbers of
active quark flavors and for different number of loops taken into
account. On basis of the stated expansion the effective method for precise
calculation of the analytic running coupling can be developed.Comment: 9 pages, LaTeX, 1 table, 1 eps figur
Nonmonotonic magnetoresistance of a two-dimensional viscous electron-hole fluid in a confined geometry
Ultra-pure conductors may exhibit hydrodynamic transport where the collective
motion of charge carriers resembles the flow of a viscous fluid. In a confined
geometry (e.g., in ultra-high quality nanostructures) the electronic fluid
assumes a Poiseuille-like flow. Applying an external magnetic field tends to
diminish viscous effects leading to large negative magnetoresistance. In
two-component systems near charge neutrality the hydrodynamic flow of charge
carriers is strongly affected by the mutual friction between the two
constituents. At low fields, the magnetoresistance is negative, however at high
fields the interplay between electron-hole scattering, recombination, and
viscosity results in a dramatic change of the flow profile: the
magnetoresistance changes its sign and eventually becomes linear in very high
fields. This novel non-monotonic magnetoresistance can be used as a fingerprint
to detect viscous flow in two-component conducting systems.Comment: 10 pages, 8 figure
Counterflows in viscous electron-hole fluid
In ultra-pure conductors, collective motion of charge carriers at relatively
high temperatures may become hydrodynamic such that electronic transport may be
described similarly to a viscous flow. In confined geometries (e.g., in
ultra-high quality nanostructures), the resulting flow is Poiseuille-like. When
subjected to a strong external magnetic field, the electric current in
semimetals is pushed out of the bulk of the sample towards the edges. Moreover,
we show that the interplay between viscosity and fast recombination leads to
the appearance of counterflows. The edge currents possess a non-trivial spatial
profile and consist of two stripe-like regions: the outer stripe carrying most
of the current in the direction of the external electric field and the inner
stripe with the counterflow.Comment: 10 pages, 5 figure
Laser in the axial electric field as a tool to search for P-, T- invariance violation
We consider rotation of polarization plane of the laser light when a gas
laser is placed in a longitudinal electric field (10~kV/cm). It is shown that
residual anisotropy of the laser cavity 10^{-6} and the sensitivity to the
angle of polarization plane rotation about 10^{-11} -10^{-12} rad allows one to
measure an electron EDM with the sensitivity about 10^{-30} e cm.Comment: 12 page
Magnetoresistance of compensated semimetals in confined geometries
Two-component conductors -- e.g., semi-metals and narrow band semiconductors
-- often exhibit unusually strong magnetoresistance in a wide temperature
range. Suppression of the Hall voltage near charge neutrality in such systems
gives rise to a strong quasiparticle drift in the direction perpendicular to
the electric current and magnetic field. This drift is responsible for a strong
geometrical increase of resistance even in weak magnetic fields. Combining the
Boltzmann kinetic equation with sample electrostatics, we develop a microscopic
theory of magnetotransport in two and three spatial dimensions. The compensated
Hall effect in confined geometry is always accompanied by electron-hole
recombination near the sample edges and at large-scale inhomogeneities. As the
result, classical edge currents may dominate the resistance in the vicinity of
charge compensation. The effect leads to linear magnetoresistance in two
dimensions in a broad range of parameters. In three dimensions, the
magnetoresistance is normally quadratic in the field, with the linear regime
restricted to rectangular samples with magnetic field directed perpendicular to
the sample surface. Finally, we discuss the effects of heat flow and
temperature inhomogeneities on the magnetoresistance.Comment: 22 pages, 7 figures, published versio
Magnetoresistance in two-component systems
Two-component systems with equal concentrations of electrons and holes
exhibit non-saturating, linear magnetoresistance in classically strong magnetic
fields. The effect is predicted to occur in finite-size samples at charge
neutrality in both disorder- and interaction-dominated regimes. The phenomenon
originates in the excess quasiparticle density developing near the edges of the
sample due to the compensated Hall effect. The size of the boundary region is
of the order of the electron-hole recombination length that is inversely
proportional to the magnetic field. In narrow samples and at strong enough
magnetic fields, the boundary region dominates over the bulk leading to linear
magnetoresistance. Our results are relevant for semimetals and narrow-band
semiconductors including most of the topological insulators.Comment: 11 pages, 3 figure
- …