PREPARATION OF VCу NANOPOWDERS OF VARIOUS PARTICAL SIZES AND COMPOSITION

Nanocrystalline powders of nonstoichiometric disordered cubic (sp. gr. Fm-3m) vanadium carbide VCy were synthesized by high-energy ball-milling and subsequent vacuum annealing. The obtained nanocrystalline powders have the particles ranging from 80 to 20 nm and different stoichiometry within its homogeneity region of VC0 6 5 to VC0 .875- The nanopowders were characterized by X-ray diffraction and scanning electron microscopy.Исследование выполнено в ИХТТ УрО РАН за счет гранта Российского научного фонда (проект № 14-23-00025)

η→π0γγ\eta \to \pi^0 \gamma \gamma decay within unitarized chiral perturbation theory

We improve the calculations of the $\eta \to \pi^0 \gamma \gamma$ decay within the context of meson chiral lagrangians. We use a chiral unitary approach for the meson-meson interaction, thus generating the $a_0(980)$ resonance and fixing the longstanding sign ambiguity on its contribution. This also allows us to calculate the loops with one vector meson exchange, thus removing a former source of uncertainty. In addition we ensure the consistency of the approach with other processes. First, by using vector meson dominance couplings normalized to agree with radiative vector meson decays. And, second, by checking the consistency of the calculations with the related $\gamma \gamma \to \pi^0 \eta$ reaction. We find an $\eta \to \pi^0 \gamma \gamma$ decay width of $0.47\pm 0.10$ eV, in clear disagreement with published data but in remarkable agreement with the most recent measurement.Comment: 15 pages, 10 figures, published versio

Isospin breaking corrections to low-energy pi-K scattering

We evaluate the matrix elements for the processes pi^0 K^0 -> pi^0 K^0 and pi^- K^+ -> pi^0 K^0 in the presence of isospin breaking terms at leading and next-to-leading order. As a direct application the releveant combination of the S-wave scattering lengths involved in the pion-kaon atom lifetime is determined. We discuss the sensitivity of the results with respect to the input parameters.Comment: 33 pages, plain latex, 2 figure

Symmetry and spin dephasing in (110)-grown quantum wells

Symmetry and spin dephasing of in (110)-grown GaAs quantum wells (QWs) are investigated applying magnetic field induced photogalvanic effect (MPGE) and time-resolved Kerr rotation. We show that MPGE provides a tool to probe the symmetry of (110)-grown quantum wells. The photocurrent is only observed for asymmetric structures but vanishes for symmetric QWs. Applying Kerr rotation we prove that in the latter case the spin relaxation time is maximal, therefore these structures set upper limit of spin dephasing in GaAs QWs. We also demonstrate that structure inversion asymmetry can be controllably tuned to zero by variation of delta-doping layer position.Comment: 4 pages, 4 figure

Energy and decay width of the pi-K atom

The energy and decay width of the pi-K atom are evaluated in the framework of the quasipotential-constraint theory approach. The main electromagnetic and isospin symmetry breaking corrections to the lowest-order formulas for the energy shift from the Coulomb binding energy and for the decay width are calculated. They are estimated to be of the order of a few per cent. We display formulas to extract the strong interaction S-wave pi-K scattering lengths from future experimental data concerning the pi-K atom.Comment: 37 pages, 5 figures, uses Axodra

The Strong Isospin-Breaking Correction for the Gluonic Penguin Contribution to epsilon'/epsilon at Next-to-Leading Order in the Chiral Expansion

The strong isospin-breaking correction, Omega_{st}, which appears in estimates of the Standard Model value for the direct CP-violating ratio epsilon'/epsilon, is evaluated to next-to-leading order (NLO) in the chiral expansion using Chiral Perturbation Theory. The relevant linear combinations of the unknown NLO CP-odd weak low-energy constants (LEC's) which, in combination with 1-loop and strong LEC contributions, are required for a complete determination at this order, are estimated using two different models. It is found that, to NLO, Omega_{st}=0.08 +/- 0.05, significantly reduced from the ``standard'' value, 0.25 +/- 0.08, employed in recent analyses. The potentially significant numerical impact of this decrease on Standard Model predictions for epsilon'/epsilon, associated with the decreased cancellation between gluonic penguin and electroweak penguin contributions, is also discussed.Comment: 12 pages, 1 figur

Magneto-gyrotropic photogalvanic effect and spin dephasing in (110)-grown GaAs/AlGaAs quantum well structures

We report the magnetogyrotropic photogalvanic effect(MPGE)in n-doped (110)-grown GaAs/AlGaAs quantum-well (QW) structures caused by free-carrier absorption of terahertz radiation in the presence of a magnetic field. The photocurrent behavior upon variation in the radiation-polarization state, magnetic field orientation, and temperature is studied. The developed theory of MPGE describes well all experimental results. It is demonstrated that the structure inversion asymmetry can be controllably tuned to zero by variation in the delta-doping layer positions. For the in-plane magnetic ield the photocurrent is only observed in asymmetric structures but vanishes in symmetrically doped QWs. Applying time-resolved Kerr rotation and polarized luminescence we investigate the spin relaxation in QWs for various excitation levels. Our data confirm that in symmetrically doped QWs the spin-relaxation time is maximal; therefore, these structures set the upper limit of spin dephasing in GaAs/AlGaAs QWs