1,112 research outputs found
Minimal cubic cones via Clifford algebras
We construct two infinite families of algebraic minimal cones in . The
first family consists of minimal cubics given explicitly in terms of the
Clifford systems. We show that the classes of congruent minimal cubics are in
one to one correspondence with those of geometrically equivalent Clifford
systems. As a byproduct, we prove that for any , , there is
at least one minimal cone in given by an irreducible homogeneous cubic
polynomial. The second family consists of minimal cones in , ,
defined by an irreducible homogeneous polynomial of degree . These examples
provide particular answers to the questions on algebraic minimal cones posed by
Wu-Yi Hsiang in the 1960's.Comment: Final version, corrects typos in Table
Violation of Lorentz Invariance and neutral component of UHECR
The observed clustering of ultra-high energy cosmic rays suggests the
existence of a neutral component. The models with violation of Lorentz
invariance may explain this component by neutrons becoming stable above some
threshold energy E_0. The protons, in turn, may become unstable above some
energy E_1>E_0. We calculate the dependence of the threshold energies E_0 and
E_1 on the parameters of the model and find E_1/E_0\gsim 1.5. We argue that the
characteristic threshold behavior of charged and neutral components may be used
as the specific signature of models with violation of Lorentz invariance. The
existence of the neutron stability threshold E_0 can be investigated with
already existing data.Comment: 14 pages, 2 figure
First-order nonthermal phase transition after preheating
During preheating after inflation, parametric resonance rapidly generates
very large fluctuations of scalar fields. In models where the inflaton field
oscillates in a double-well potential and interacts with another scalar
field , fluctuations of X can keep the \phi to -\phi symmetry temporarily
restored. If the coupling of \phi to X is much stronger than the inflaton
self-coupling, the subsequent symmetry breaking is a first-order phase
transition. We demonstrate the existence of this nonthermal phase transition
with lattice simulations of the full nonlinear dynamics of the interacting
fields. In particular, we observe nucleation of an expanding bubble.Comment: RevTeX, 4 page
The modern methods of reproduction physiology of horses
The concept of development of horse breeding in Ukraine until 2020 provides for an increase in the number of horses through the intensive use of modern methods of reproduction biotechnology. However, the imperfection of these methods hinders their widespread use in practice. The aim of the work was to draw attention to the most important problems of the physiology of horse reproduction in Ukraine and to show ways to solve them that have already been proposed by domestic and foreign researchers. The development strategy of the physiology of horse reproduction in order to increase its effectiveness should take into account the least studied aspects that were discussed above. The article shows that taking into account the influence of micromycetes, the absolute number of colony forming units of E. coli in semen of stallions; immuno-and cytogenetic features; new methods of sanitary preparation of horses for sperm and insemination; the effect of permissible levels of feed mycotoxins on physiological functions improves the efficiency of equine reproduction physiology methods. However, we first discovered new physiological features of the effect of erythrocyte antigens of blood groups of horses of Ukrainian selection on the indicators of their native sperm. In the presence of ad/bcm and dg/cgm alleles of the blood group D system in stallions, sperm motility is on average less than 5 points; alleles ad/cgm, ad/d, ad/de, ad/dk, bcm/d, bcm/de, bcm/dg, bcm/dk, cegm/cgm, cegm/d, cegm/dg, cegm/dk, cgm/ceg, cgm/cgm, cgm/dg, cgm/dk, de/cgm, de/dk, dg/di, dk/d, dk/de, dk/dk is accompanied by sperm motility from 5 to 7 points; alleles bcm/cgm, dg/dk, de/d, cgm/d, cgm/de sperm motility is observed more than 7 points. The results obtained allowed us to develop for practice ways to increase the efficiency of sperm cryopreservation by immunogenetic parameters. In addition, open physiological correlations can increase the fertility of mares during mating
Reheating and thermalization in a simple scalar model
We consider a simple model for the Universe reheating, which consists of a
single self--interacting scalar field in Minkowskian space--time. Making use of
the existence of an additional small parameter proportional to the amplitude of
the initial spatially homogeneous field oscillations, we show that the behavior
of the field can be found reliably. We describe the evolution of the system
from the homogeneous oscillations to the moment when thermalization is
completed. We compare our results with the Hartree--Fock approximation and
argue that some properties found for this model may be the common features of
realistic theories.Comment: Some changes in Introduction and Discussion, comparison with the
Hartree--Fock results added. 37 pages, 2 postscript figures attache
Evolution of the Order Parameter after Bubble Collisions
If a first-order phase transition is terminated by collisions of new-phase
bubbles, there will exist a period of nonequilibrium between the time bubbles
collide and the time thermal equilibrium is established. We study the behavior
of the order parameter during this phase. We find that large nonthermal
fluctuations at this stage tend to restore symmetry, i.e., the order parameter
is smaller than its eventual thermal equilibrium value. We comment on possible
consequences for electroweak baryogenesis.Comment: 11 page LaTeX file with two figures, fig1.ps and fig2.p
Resonant Production of Topological Defects
We describe a novel phenomenon in which vortices are produced due to resonant
oscillations of a scalar field which is driven by a periodically varying
temperature T, with T remaining much below the critical temperature .
Also, in a rapid heating of a localized region to a temperature {\it below}
, far separated vortex and antivortex can form. We compare our results
with recent models of defect production during reheating after inflation. We
also discuss possible experimental tests of our predictions of topological
defect production {\it without} ever going through a phase transition.Comment: Revtex, 13 pages including 5 postscript figure
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