Ferromagnetism in the Highly-Correlated Hubbard Model

The Hubbard model with strong correlations is treated in the many-electron representation of Hubbard's operators. The regions of stability of saturated and non-saturated ferromagnetism in the n-U plane for the square and simple cubic lattices are calculated. The role of the bare density of states singularities for the magnetic phase diagram is discussed. A comparison with the results of previous works is performed.Comment: Report on IV Euro-Asian Symposium "Trends in MAGnetism" EASTMAG-2010, Ekaterinburg; 4 pages, pd

Coherent and Non-Coherent Double Diffractive Production of QQˉ Q \bar {Q} - pairs in Collisions of Heavy Ions at High Energies

The double coherent and non-coherent diffractive production of heavy quark - antiquark pairs ($Q \bar{Q}$) in heavy ion scattering at high energies (LHC) is considered. The total and differential cross sections of these processes with the formation of $c \bar{c}$ and $b \bar{b}$ pairs in $pp$, $CaCa$ and $PbPb$ collisions are evaluated. The contribution of the considered mechanisms is a few per cent of the number of heavy quark - antiquark pairs obtained in the processes of hard (QCD) scattering, and it will be taken into account in the registration of $c$, $b$ quarks or, for instance, in the study of the heavy quarkonia suppression effects in Quark - Gluon Plasma, in the search for intermediate mass Higgs bosons and so on. It is shown that the cross section of the coherent scattering process is great enough. This makes it suitable for studying collective effects in nuclear interactions at high energies. An example of such effects is given: large values of the invariant mass of a $Q \bar{Q}$pair, M_{Q \bar{Q}} \gsim 100 GeV, in association with a large rapidity gap between diffractive jets $\Delta \eta > 5$.Comment: 22 pages, 5(.eps) figures, 3 tables, LaTe