17,644 research outputs found
Multidimensional Worldline Instantons
We extend the worldline instanton technique to compute the vacuum pair
production rate for spatially inhomogeneous electric background fields, with
the spatial inhomogeneity being genuinely two or three dimensional, both for
the magnitude and direction of the electric field. Other techniques, such as
WKB, have not been applied to such higher dimensional problems. Our method
exploits the instanton dominance of the worldline path integral expression for
the effective action.Comment: 22 pages, 13 figure
Polarization of the electron and positron produced in combined Coulomb and strong laser fields
The process of production in the superposition of a Coulomb and a
strong laser field is considered. The pair production rate integrated over the
momentum and summed over the spin projections of one of the particles is
derived exactly in the parameters of the laser field and in the Born
approximation with respect to the Coulomb field. The case of a monochromatic
circularly polarized laser field is considered in detail. A very compact
analytical expression of the pair production rate and its dependence on the
polarization of one of the created particles is obtained in the quasiclassical
approximation for the experimentally relevant case of an undercritical laser
field. As a result, the polarization of the created electron (positron) is
derived.Comment: 16 pages, no figure
How to make a mature accreting magnetar
Several candidates for accreting magnetars have been proposed recently by
different authors. Existence of such systems contradicts the standard magnetic
field decay scenario where a large magnetic field of a neutron star reaches
fewG at ages Myr. Among other sources,
the high mass X-ray binary 4U0114+65 seems to have a strong magnetic field
around G. We develop a new Bayesian estimate for the kinematic age
and demonstrate that 4U0114+65 has kinematic age 2.4-5 Myr ( credential
interval) since the formation of the neutron star. We discuss which conditions
are necessary to explain the potential existence of magnetars in accreting
high-mass binaries with ages about few Myrs and larger. Three necessary
ingredients are: the Hall attractor to prevent rapid decay of dipolar field,
relatively rapid cooling of the crust in order to avoid Ohmic decay due to
phonons, and finally, low values of the parameter to obtain long Ohmic time
scale due to impurities. If age and magnetic field estimates for proposed
accreting magnetars are correct, then these systems set the strongest limit on
the crust impurity for a selected sample of neutron stars and provide evidence
in favour of the Hall attractor.Comment: 8 pages, 3 figures, accepted to MNRAS on September 2
Atomic coherence and interference phenomena in resonant nonlinear optical interactions
Interference effects in quantum transitions, giving rise to amplification
without inversion, optical transparency and to enhancements in nonlinear
optical frequency conversions are considered. Review of the relevant early
theoretical and experimental results is given. The role of relaxation
processes, spontaneous cascade of polarizations, local field effects,
Doppler-broadening, as well as specific features of the interference in the
spectral continuum are discussed.Comment: 13 pages, 13 eps figures, review paper, Proceedings of the 15th
International Conference on Nonlinear Optics - ICONO'9
Hyperbolic carbon nanoforest for phase matching of ordinary and backward electromagnetic waves: second harmonic generation
We show that deliberately engineered dispersive metamaterial slab can enable
the co-existence and phase matching of contra-propagating ordinary fundamental
and extraordinary backward second harmonic surface electromagnetic modes.
Energy flux and phase velocity are contra-directed in the backward waves which
is the phenomenon that gives rise to unique nonlinear optical propagation
processes. We show that frequencies, phase, and group velocities, as well as
nanowaveguide losses inherent to the electromagnetic modes supported by such
metamaterial, can be tailored to maximize conversion of frequencies and to
reverse propagation direction of the generated wave. Such a possibility, which
is of paramount importance for nonlinear photonics, is proved with a numerical
model of the hyperbolic metamaterial made of carbon nanotubes standing on the
metal surface. Extraordinary properties of the backward-wave second harmonic
generation in the reflection direction and of the corresponding frequency
doubling metareflector in the THz are investigated with a focus on the pulsed
regime.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1602.0249
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