6,647 research outputs found
Possible Odderon discovery at HERA via charge asymmetry in the diffractive pi+pi- production
We discuss how the evasive Odderon signal can be enhanced by final state
interactions. We suggest the charge asymmetry of pion spectra in diffractive
pi+pi- photoproduction as a promising signature of the Odderon exchange.Comment: 4 pages, To appear in Proceedings of the 9th International Workshop
on Deep Inelastic Scattering (DIS2001), Bologna, Italy, 27 Apr. - 1 May 200
Double-exchange theory of ferroelectric polarization in orthorhombic manganites with twofold periodic magnetic texture
We argue that many aspects of improper ferroelectric activity in orthorhombic
manganites can be rationalized by considering the limit of infinite
intra-atomic splitting between the majority- and minority-spin states (or the
double exchange limit), which reduces the problem to the analysis of a spinless
double exchange (DE) Hamiltonian. We apply this strategy to the low-energy
model, derived from the first-principles calculations, and combine it with the
Berry-phase theory of electric polarization. We start with the simplest
two-orbital model, describing the behavior of the eg bands, and apply it to the
E-type antiferromagnetic (AFM) phase, which in the DE limit effectively breaks
up into one-dimensional zigzag chains. We derive an analytical expression for
the electronic polarization (Pel) and explain how it depends on the orbital
ordering and the energy splitting Delta between eg states. Then, we evaluate
parameters of this model, starting from a more general five-orbital model for
all Mn 3d bands and constructing a new downfolded model for the eg bands. From
the analysis of these parameters, we conclude that the behavior of Pel in
realistic manganites corresponds to the limit of large Delta. We further
utilize this property in order to derive an analytical expression for Pel in a
general two-fold periodic magnetic texture, based on the five-orbital model and
the perturbation-theory expansion for the Wannier functions in the first order
of 1/Delta. This expression explains the functional dependence of Pel on the
relative directions of spins. Furthermore, it suggests that Pel is related to
the asymmetry of the transfer integrals, which should simultaneously have
symmetric and antisymmetric components. Finally, we explain how the
polarization can be switched between orthorhombic directions a and c by
inverting the zigzag AFM texture in every second ab plane.Comment: 41 page, 10 figure
Spin dependence of ferroelectric polarization in the double exchange model for manganites
The double exchange (DE) model is systematically applied for studying the
coupling between ferroelectric (FE) and magnetic orders in several prototypical
types of multiferroic manganites. The model was constructed for the
magnetically active Mn bands in the basis of Wannier functions and include
the effect of screened on-site Coulomb interactions. The essence of our
approach for the FE polarization is to use the Berry phase theory, formulated
in terms of occupied Wannier functions, and to evaluate the asymmetric
spin-dependent change of these functions in the framework of the DE model. This
enables us to quantify the effect of the magnetic symmetry breaking and derive
several useful expressions for the electronic polarization , depending
on the relative directions of spins. The proposed theory is applied to the
solution of three major problems: (i) The magnetic-state dependence of in hexagonal manganites; (ii) The microscopic relationship between canted
ferromagnetism and in monoclinic BiMnO; (iii) The origin of FE
activity in orthorhombic manganites. We show that for an arbitrary noncollinear
magnetic structure, propagating along the orthorhombic axis
and antiferromagnetically coupled , can be obtained
by scaling the one of the E-phase with the prefactor depending only on the
relative directions of spins and being the measure of the spin inhomogeneity.
This picture works equally well for the twofold (HoMnO) and fourfold
(TbMnO) periodic manganites. The basic difference is that the twofold
periodic magnetic structure is strongly inhomogeneous, that leads to large
. On the contrary, the fourfold periodic magnetic structure can be
viewed as a moderately distorted homogeneous spin spiral, which corresponds to
weaker .Comment: 32 pages, 7 figure
Initial dynamics of the EKG during an electrical defibrillation of the heart
In tests on 11 mature dogs, immobilized by means of an automatic blocking and synchronization system, artefact free EKG were obtained, beginning 0.04-0.06 sec after passage of a defibrillating current. Different versions of the start of fibrillation were noted, in application of the defibrillating stimulus in the early phase of the cardiac cycle. A swinging phenomenon, increasing amplitude, of fibrillation was noted for 0.4-1.5 sec after delivery of a subthreshold stimulus. Conditions for a positive outcome of repeated defibrillation were found, and a relationship was noted between the configuration of the exciting process with respect to the lines of force of the defibrillating current and the defibrillation threshold. It was shown that the initial EKG dynamics after defibrillation is based on a gradual shift of the pacemaker from the myocardium of the ventricles to the sinus node, through phases of atrioventricular and atrial automatism
NLO evolution of color dipoles
The small- deep inelastic scattering in the saturation region is governed
by the non-linear evolution of Wilson-line operators. In the leading
logarithmic approximation it is given by the BK equation for the evolution of
color dipoles. In the next-to-leading order the BK equation gets contributions
from quark and gluon loops as well as from the tree gluon diagrams with
quadratic and cubic nonlinearities. We calculate the gluon contribution to
small-x evolution of Wilson lines (the quark part was obtained earlier).Comment: 43 pages, 12 figure
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