The characteristic system for the Euler - Poisson's equations

In this paper we investigate the nonlinear system naturally connected with the Euler - Poisson's equations. The solutions of this system may be used for description of the singular points to the Euler - Poisson's equations

Quark-Hadron Duality and γ∗p→Δ\gamma^* p \to \Delta Form Factors

We use local quark-hadron duality to estimate the purely nonperturbative soft contribution to the $\gamma^*p\to \Delta$ form factors. Our results are in agreement with existing experimental data. We predict that the ratio $G_E^*(Q^2)/G_M^*(Q^2)$ is small for all accessible $Q^2$, in contrast to the pQCD expectations that $G_E^*(Q^2)\to -G_M^*(Q^2)$.Comment: 15 pages, LaTeX + 4 PS-figures enclosed in one uuencoded, compressed fil

ERRATUM TO: Power corrections 1/Q21/Q^2 to parton sum rules for deep inelastic scattering from polarized targets

We clarify conflicting results in the literature on coefficient functions in front of higher twist operators contributing to the parton sum rules for deep inelastic scattering from polarized targets. The necessary corrections do not affect our calculations of matrix elements, published in Phys.Lett.B242(1990)245, but change final estimates of the $\sim 1/Q^2$ contributions to Bjorken and Ellis--Jaffe sum rules.Comment: 2 pages, MPI-Ph/93-0

On Possible Light-Torsion Mixing in Background Magnetic Field

The interaction of the light with propagating axial torsion fields in the presence of an external magnetic field has been investigated. Axial torsion fields appearing in higher derivative quantum gravity possess two states, with spin one and zero, with different masses. The torsion field with spin-0 state is a ghost that can be removed if its mass is infinite. We investigate the possibility when the light mixes with the torsion fields resulting in the effect of vacuum birefringence and dichroism. The expressions for ellipticity and the rotation of light polarization axis depending on the coupling constant and the external magnetic field have been obtained.Comment: 12 pages, title changed, shortened journal version, accepted in Eur.Phys.J.

Negative pion photoproduction off polarized deuteron target

It is discussed whether the target asymmetry (TA) for γn→π⁻p can be extracted from data on γd→π⁻pp. An exclusive experiment that enhances production of pions on neutron at rest and suppresses contributions of the recoil mechanism is shown to correspond to this purpose. The relation between the TAs for the reactions on deuteron and neutron is established taking into account pion and active nucleon rescattering in the final state and neglecting effects due to interaction with the spectator nucleon

Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering

We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. A remarkable agreement is found between the calculated and the experimentally measured u-quark distribution up to light-cone distances $\Delta^- = \Delta^0 - \Delta^3$ of order $\sim 1$ fm in the proton rest frame. The calculation for valence d quarks gives much worse results; the reasons for this discrepancy are discussed.Comment: 24 pages plus 13 pages with figures, requires epsf.sty, revised version to appear in Phys.Rev.

Phase of the Wilson Line at High Temperature in the Standard Model

We compute the effective potential for the phase of the Wilson line at high temperature in the standard model to one loop order. Besides the trivial vacua, there are metastable states in the direction of $U(1)$ hypercharge. Assuming that the universe starts out in such a metastable state at the Planck scale, it easily persists to the time of the electroweak phase transition, which then proceeds by an unusual mechanism. All remnants of the metastable state evaporate about the time of the $QCD$ phase transition.Comment: 4 pages in ReVTeX plus 1 figure; Columbia Univ. preprint CU-TP-63

D∗DπD^*D\pi and B∗BπB^*B\pi couplings in QCD

We calculate the $D^*D\pi$ and $B^*B\pi$ couplings using QCD sum rules on the light-cone. In this approach, the large-distance dynamics is incorporated in a set of pion wave functions. We take into account two-particle and three-particle wave functions of twist 2, 3 and 4. The resulting values of the coupling constants are $g_{D^*D\pi}= 12.5\pm 1$ and $g_{B^*B\pi}= 29\pm 3$. From this we predict the partial width \Gamma (D^{*+} \ra D^0 \pi^+ )=32 \pm 5~ keV . We also discuss the soft-pion limit of the sum rules which is equivalent to the external axial field approach employed in earlier calculations. Furthermore, using $g_{B^*B\pi}$ and $g_{D^*D\pi}$ the pole dominance model for the B \ra \pi and D\ra \pi semileptonic form factors is compared with the direct calculation of these form factors in the same framework of light-cone sum rules.Comment: 27 pages (LATEX) +3 figures enclosed as .uu file MPI-PhT/94-62 , CEBAF-TH-94-22, LMU 15/9