The Dyson-Schwinger equations in the instanton vacuum of the Schwinger model

Using the exact path integral solution of the Schwinger model — a model where instantons are present — the Dyson-Schwinger equations are shown to hold by explicit computation. It turns out that the Dyson-Schwinger equations separately hold for every instanton sector. This is due to the invariance of the Schwinger model.Supported by Fonds zur Förderung der wissenschaftlichen Forschung in Österreich, Projekt Nr.P8444-TEC.     

Genuine twist-3 contributions to the generalized parton distributionsfrom instantons

The genuine twist-3 quark-gluon ( ) contributions to the generalized parton distributions (GPDs) are estimated in the model of the instanton vacuum. These twist-3 effects are found to be parametrically suppressed relative to the kinematical twist-3 ones due to the small packing fraction of the instanton vacuum. We derived exact sum rules for the twist-3 GPDs.Received: 21 April 2004, Published online: 6 August 2004     

A unified formalism for γγ→meson and ψ-γX with possible tests for hybrid and gluonic hadrons

The couplings of conventional and hybrid mesons to (real and virtual) and their production amplitudes in M are described in a unified manner. Existing results for heavy quarks are recovered, extensions to light quarks and to virtual couplings are made and phenomenological applications discussed. In particular we discuss relativistic corrections to 0⁺, 1⁺, 2⁺ for both real and virtual photons and offer a resolution to a long standing puzzle in perturbative QCD concerning the helicity structure of 2⁺⁺. We suggest that the production off ₂ (1720) involves gluons in an essential way or that this meson hasJ2.     

Study of theπ + π − γ system centrally produced in the reactionpp→p f (π + π − γ)p s at 300 GeV/c

The reactionppp _f ( ^{+ –} )p _s , where the ^{+ –} system is centrally produced, has been studied at 300 GeV/c. The ^{+ –} mass spectrum shows evidence for a ⁰ decay mode of the (958) andf ₁ (1285). The branching ratio (f ₁(1285) ^{+ +})/(f ₁(1285) ⁰ ) is found to be 5.0±0.7. No evidence is found for a ⁰(770) decay mode of theE/f ₁ (1420) for which an upper limit BR (E/f ₁(1420) ⁰ )<0.08 at=" 95%=" cl=" is=">     

High-spin states in121Te

The baryon density calculated at the collision center in relativistic heavy ion collisions is not representative for the density really probed by baryons in the high density collision phase. A decomposition into nucleon- and-resonance densities yields average values of 1.25N/o and 0.25/ ₀ at the time of maximum compression.work supported by GSI and BMFT     

Creation of Closed or Open Universe from Constrained Instanton

In the no-boundary universe the universe is created from an instanton. However, no instanton exists for the realistic FRW universe with a scalar field. The instanton leading to its quantum creation may be modified and reinterpreted as a constrained gravitational instanton.     

Analysis of the results of calibrating meteoritic olivine crystals with238U nuclei at the Bevalac accelerator

The results are presented of calibrating the sensitivity of olivine crystals from meteorites by the²³⁸U nuclei produced at the Bevalac accelerator. The comparative studies of the spectra of the etchable track lengths due to the²³⁸U nuclei and to fossil tracks in these olivines have shown that the group of the 210 m fossil tracks observed in 1980 at the LNR, JINR is due to the galactic cosmic-ray nuclei of the Th-U group. As regards the origin of the 340–360 m group of fossil tracks which were considered in [2] to be candidates for superheavy nuclei in cosmic rays the presence of the track with a length of up to 360 m in the calibrating²³⁸U track length spectra indicates that the above interpretation has to be questioned. The possible ways of the unambiguous identification of the group of the abnormally long fossil tracks are discussed.In conclusion the authors express their deep gratitude to Academician G.N. Flerov for thoughtful guidance and permanent attention to this study. The authors wish to thank Dr. G.M. Ter-Akopian for very useful discussions and advice and also for his help during the calibrations on Bevalac, Dr. R.I. Petrova for her help in preparing olivine crystal mounts and for their subsequent annealing and etching, and Mrs. G.G. Bankova and G.P. Knyazeva for the thorough microscopic measurements of the²³⁸U track spectra.     

Extended operator expansion method for neutrinoless double beta decay

Reliable calculations of nuclear matrix elements are a prerequisite for the determination of the effective neutrino mass and other particle physics parameters from neutrinoless double beta decay. Here, the operator expansion method is improved by including Coulomb, tensor and central interactions simultaneously. Furthermore, the formalism of the OEM is extended to those matrix elements necessary to extract the right-handed parameters and from 0 decay. OEM includes the dependence of the nuclear matrix elements on the intermediate states implicitly and can therefore be understood as a step beyond the closure approximation. Numerical studies are carried out for the isotope⁷⁶Ge combining the OEM expressions with ground-state wave functions calculated within a proton-neutron quasiparticle Random Phase Approximation (pn-QRPA) model. The influence and relative importance of central, tensor and Coulomb interactions is investigated. Within the OEM, contributions from the Coulomb force are found to be negligible in 0 decay, while the tensor force leads to a moderate change of the results, of the order of (10–30)%, giving a better agreement between sets of calculations which employ different NN-interactions. Generally, results of the OEM+QRPA calculation are similar to previous calculations of 0 decay matrix elements, indicating that 0 decay is not sensitive to model approximations and might therefore be more accurately calculated than the strongly suppressed 2 decay matrix elements.     

The analytic structure of the anomalous dimension of the four-gluon operator in deep inelastic scattering

The phenomenology of the pseudoscalar (1440) meson (also known as l) is discussed in a simplified , l mixing scheme in which the is assumed to have no glueball component. The parameters of the model are quite well constrained from the and two-photon decays. First it is shown that the scheme is in rather good general agreement with (almost) all the available data. Then a number of testable predictions concerning decays involving the iota are made. The iota turns out to be largely a glueball in this model.     

Spin and parity of isomeric and ground states of the doubly-odd nucleus184Au

Low-spin states in doubly-odd¹⁸⁴Au have been populated in the ⁺/EC decay of¹⁸⁴Hg produced by bombarding¹⁸⁴Sm targets with an 185 MeV⁴⁰Ar beam. Radioactive Hg nuclei were transported by a He jet system. A new level scheme has been established from --t and X--t coincidence measurements. Spin and parity values I=5⁺, I =2⁺ and I=3^– were assigned to the ground state and the two isomeric states of¹⁸⁴Au, respectively. The structure of these states is discussed using B(E1) values.     

A measurement of the π0, η and η′ electromagnetic form factors

We present measurement of the ^0*, ^* and ^* form factors. The ⁰-form factor is for the first time observed in the space-like region. The transition form factor of the -meson is determined from its decay modes ^+–0, ^+– and the neutral decay mode . The decay of the is observed in the decay channels , ^+– with and in the four charged prong final state stemming from ^+– with the decaying into ^+–(⁰/). All form factors agree well with a simple -pole predicted by the vector meson dominance model and also with the QCD inspired Brodsky-Lepage model.     

LargeP T P−P collisions to probe the gluonic and sea spin distribution in the proton

We parametrise the polarised gluon and sea distribution functions incorporating the interpretation of the EMC experiment that, due to the axial anomaly the observed quark contribution to proton spin at Q ²>=10.7 GeV². Typical processes to isolate the gluonic and sea content of the proton studied here are the largeP _T direct photon production processes (a) using single polarized protonPPX and (b) polarized beam and target protonPPX. In both the above process the dominant contribution comes from the Compton subprocess and so can be used as a clean probe of the gluonic content of the proton. LargeP _T muon pair production PP(^+–)X are also studied and we find that the annihilation subprocess dominates, but not much larger than the Compton subprocess and so may not be a clean probe of the sea content of the proton. The effect of two loop corrections to the parametrisation and asymmetries are also considered, and are found to be negligible.     

Masses of colored vector mesons

Mass formulas for colored vector mesons are derived under the assumption of one common mixing angle forSU(3), independent of the color quantum numbers, and correspondingly one common mixing angle () forSU(3). This a priori plausible assumption turns out to have strong implications and thus might be too restrictive. We allow for a non-trivial spatial overlap integral between color-singlet and color-octet states. Various cases are treated and physical possibilities are identified. The best agreement is obtained for = 0. There are two models of this type with and without a part of the symmetry breaking Hamiltonian density transforming as (Y, Y) underSU(3)SU(3). Models with 0 are also possible. They cannot have a (Y, Y) and predict 3.34 GeV as the mass of the (3.7). This error of 10% may however be used to reject this possibility. Masses of colored vector mesons are predicted in the various models. If a (Y, Y) is present, ideal mixing inSU (3) is implied by the general formalism of the model.     

Deep inelastic compton-scattering with polarized beam and target

The helicity difference of the photon photoproduction process px is calculated using four different polarized proton structure functions. Also discussed are the contributions originating from the Compton cross-section and the subprocesses of induced by photon structure and fragmentation. Up-quark and gluondominance can be separated by choosing different regions of pseudorapidity and normalized transverse momentumX _T of the final-state photon. We show, that it is possible to distinguish between the two extreme models of proton spin: polarized gluon vice polarized strange-quark.