1,888 research outputs found
Generic coverings of plane with A-D-E-singularities
We generalize results of the paper math.AG/9803144, in which Chisini's
conjecture on the unique reconstruction of f by the curve B is investigated.
For this fibre products of generic coverings are studied. The main inequality
bounding the degree of a covering in the case of existence of two nonequivalent
coverings with the branch curve B is obtained. This inequality is used for the
proof of the Chisini conjecture for m-canonical coverings of surfaces of
general type for .Comment: 43 pages, 20 figures; to appear in Izvestiya Mat
Magnetic degeneracy and hidden metallicity of the spin density wave state in ferropnictides
We analyze spin density wave (SDW) order in iron-based superconductors and
electronic structure in the SDW phase. We consider an itinerant model for
Fe-pnictides with two hole bands centered at and two electron bands
centered at and in the unfolded BZ. A SDW order in such a
model is generally a combination of two components with momenta and
, both yield order in the folded zone. Neutron
experiments, however, indicate that only one component is present. We show that
or order is selected if we assume that only one hole band
is involved in the SDW mixing with electron bands. A SDW order in such 3-band
model is highly degenerate for a perfect nesting and hole-electron interaction
only, but we show that ellipticity of electron pockets and interactions between
electron bands break the degeneracy and favor the desired or
order. We further show that stripe-ordered system remains a metal for
arbitrary coupling. We analyze electronic structure for parameters relevant to
the pnictides and argue that the resulting electronic structure is in good
agreement with ARPES experiments. We discuss the differences between our model
and model of localized spins.Comment: reference list updated, typos are correcte
Lateral distribution on charged particles in EAS
Lateral distribution of charged particles which allow for the finiteness of energy gamma-quanta, the inhomogeneity of the atmosphere and the experimental selection of EAS are needed to interpret experimental data. The effects of finiteness of energy of gamma-quanta which produce the partial electron-photon cascades were considered by substituting K R sub m instead of R sub m in NKG approximation where K was found to be 0.56 from comparison with the experimental data. New results on the lateral distribution of electrons in the partial cascades from gamma-quanta were obtained. It is shown that the coefficient K can be regarded as a constant. The last approximation of K was found to be most adequate when compared with the experimental data. The inhomogeneity of the atmosphere, muons and experimental selection are considered. The calculation of Ne are extended from 100,000 to 10 million for sea level and for Akeno level
Interplay between magnetism and superconductivity in Fe-pnictides
We consider phase transitions and potential co-existence of spin-density-wave
(SDW) magnetic order and extended s-wave () superconducting order within a
two-band itinerant model of iron pnictides, in which SDW magnetism and
superconductivity are competing orders. We show that depending on parameters,
the transition between these two states is either first order, or involves an
intermediate phase in which the two orders co-exist. We demonstrate that such
co-existence is possible when SDW order is incommensurate.Comment: 5 pages, 3 figure
The possibility of Z(4430) resonance structure description in reaction
The possible description of Z(4430) as a pseudoresonance structure in reaction, is considered. The analysis is performed with
single-scattering contribution to elastic scattering via
intermediate energy.Comment: 3 pages, 4 figure
Search for the gamma-ray fluxes with energies above 10915) eV from various objects
Considerable interest has developed in the search for local sources of superhigh-energy gamma-rays. The experimental data obtained with the extensive air showers (EAS) array of the Moscow State University are analyzed with a view to searching for the superhigh-energy gamma-rays from various objects and regions of the Galaxy
NN Interaction JISP16: Current Status and Prospect
We discuss realistic nonlocal NN interactions of a new type - J-matrix
Inverse Scattering Potential (JISP). In an ab exitu approach, these
interactions are fitted to not only two-nucleon data (NN scattering data and
deuteron properties) but also to the properties of light nuclei without
referring to three-nucleon forces. We discuss recent progress with the ab
initio No-core Shell Model (NCSM) approach and respective progress in
developing ab exitu JISP-type NN-interactions together with plans of their
forthcoming improvements.Comment: 9 pages, 3 figures, to be published in Proceedings of Few-body 19
conferenc
Superconductivity and spin-density-waves in multi-band metals
We present a detailed description of two-band quasi-2D metals with s-wave
superconducting (SC) and antiferromagnetic spin-density wave (SDW)
correlations. We present a general approach and use it to investigate the
influence of the difference between the shapes and the areas of the two Fermi
surfaces on the phase diagram. In particular, we determine the conditions for
the co-existence of SC and SDW orders at different temperatures and dopings. We
argue that a conventional s-wave SC order co-exists with SDW order only at very
low and in a very tiny range of parameters. An extended s-wave
superconductivity, for which SC gap changes sign between the two bands,
co-exists with antiferromagnetic SDW over a much wider range of parameters and
temperatures, but even for this SC order the regions of SDW and SC can still be
separated by a first order transition. We show that the co-existence range
becomes larger if SDW order is incommensurate. We apply our results to
iron-based pnictide materials, in some of which co-existence of SDW and SC
orders has been detected.Comment: 18 figures, 22 pages, published version with minor correction
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