Pair creation by a photon in a strong magnetic field

The process of pair creation by a photon in a strong magnetic field is investigated basing on the polarization operator in the field. The total probability of the process is found in a relatively simple form. The probability exhibits a "saw-tooth" pattern because of divergences arising when the electron and positron are created at threshold of the Landau energy levels. The pattern will be washed out at averaging over any smooth photon energy distribution. The new results are obtained in the scope of the quasiclassical approach: 1) in the case when the magnetic field $B \ll B_0, (B_0$ is the critical field) the new formulation extends the photon energy interval to the case when the created particles are not ultrarelativistic; 2) the correction to the standard quasiclassical approximation is found showing the range of applicability of the approach at high photon energy as well. The very important conclusion is that for both cases $B \ll B_0$ and $B \geq B_0$ the results of the quasiclassical calculation are very close to averaged probabilities of exact theory in a very wide range of photon energies. The quasiclassical approximation is valid also for the energy distribution if the electron and positron are created on enough high levels.Comment: 21 pages, 6 figure

Mass dependence of nuclear shadowing at small Bjorken-x from diffractive scattering

We calculate the nuclear shadowing ratio for a wide range of nuclei at small Bjorken-x in the framework of Gribov theory. The coherent contribution to the (virtual) photon-nucleon cross section is obtained in terms of the diffractive dissociation cross section. Information on diffraction from FNAL and HERA is used. Our results are compared to available experimental data from the NMC and E665 experiments at x ~ 10^{-4}.Comment: To be published in Phys. Rev.

Dynamics of two-component electromagnetic and acoustic extremely short pulses

The distinctive features of passing the two-component extremely short pulses through the nonlinear media are discussed. The equations considered describe the propagation in the two-level anisotropic medium of the electromagnetic pulses consisting of ordinary and extraordinary components and an evolution of the transverse-longitudinal acoustic pulses in a crystal containing the paramagnetic impurities with effective spin S=1/2. The solutions decreasing exponentially and algebraically are studied.Comment: LaTeX, 11 pages, 6 figure

Delbr\"uck scattering in combined Coulomb and laser fields

We study Delbr\"uck scattering in a Coulomb field in the presence of a laser field. The amplitudes are calculated in the Born approximation with respect to the Coulomb field and exactly in the parameters of the laser field having arbitrary strength, spectral content and polarization. The case of high energy initial photon energy is investigated in detail for a monochromatic circularly polarized laser field. It is shown that the angular distribution of the process substantially differs from that for Delbr\"uck scattering in a pure Coulomb field. The value of the cross section under discussion may exceed the latter at realistic laser parameters that essentially simplify the possibility of the experimental observation of the phenomenon. The effect of high order terms in the quantum intensity parameter $\chi$ of the laser field is found to be very important already at relatively small $\chi$.Comment: 21 pages, 4 figure

Search for the scalar a_0 and f_0 mesons in the \phi radiative decays

The potentialities of the production of the $a_0$ and $f_0$ mesons in the $\phi$ radiative decays are considered based on a new two-channel analysis of the $\pi\pi$ scattering in a energy region near 1 GeV. We predict $BR(\phi\to\gamma f_0(980))\sim10^{-5}-10^{-4}$ that is a great value for the decay forbidden by the Okubo-Zweig-Iizuka rule. We discuss the four-quark, $K\bar K$-molecule and two-quark scenarios for the $a_0$ and $f_0$ mesons. It is presented arguments that the $e^+e^-$-colliders and especially the $\phi$ factories give the possibility to choose a single one out of them.Comment: Talk given at HADRON-9

Two new type surface polaritons excited into nanoholes in metal films

First, we argue that the smooth metal-air interface should be regarded as a distinct dielectric medium, the skin of the metal. The existence of this metal skin leads to theoretical explanation of experimental data on the excitation of electromagnetic surface shape resonances in lamellar metallic gratings by light in the visible to near-infrared range. Surface polaritons have been observed in reflection modes on metallized gratings where the electric field is highly localized inside the grooves (around 300-1000 times larger than intensity of incoming optical light). Here we present quantized Maxwell's equations for electromagnetic field in an isotropic homogeneous medium, allowing us to solve the absorption anomaly property of these metal films. The results imply the existence of light boson particles with spin one and effective mass $m= 2.5\cdot 10^{-5} m_e$. We also show the presence of two new type surface polaritons into nanoholes in metal films.Comment: 10 pages. Accepted on November 30, 2009 in Progress in Physic

Intrinsic tunneling or Joule heating?

It is shown that the `tunnelling spectra' reported by Yurgens et al. could be reproduced qualitatively and quantitatively using the experimental out-of-plane normal state resistance R(T) and assuming that the heating of the mesa, caused by the Joule dissipation, is the only reason for effects observed at high bias.Comment: Comment on 'Intrinsic Tunneling Spectra of Bi2201 by A.Yurgens et al., Phys. Rev. Lett. 90, 147005, (2003); typo correcte