118624427
Photon and pion scattering on the basis of quark models
Within the framework of constituent quark models of simple and complex hadrons it is possible to investigate the interrelations of scattering observables and dynamical assumptions about the underlying quark structure of the participating hadrons. In the case of simple hadrons, here baryons, the inclusion of the coupling of bound q3-states to meson-baryon decay channels, accounts for the full complexity of the fact that all excited baryonic states are in fact resonances. We present here such a description of the baryonic excitation spectrum within the non-relativistic quarkmodel with all terms of the Fermi-Breit interaction. In this case the very hadronic vertices that are responsible for the dressing of hadrons also provide a semi realistic description of various scattering observables for pion scattering and photo-production of pions. The treatment of more complex hadronic systems within the framework of a quark shell model of nuclei is then used to investigate the role of the quark Pauli principle in intermediate energy excitations of nuclei with pionic or photonic probes.
120745638
SHORT-RANGE CORRELATIONS AND ELASTIC ELECTRON SCATTERING.
117998395
Quark excitations of nuclei - A new frontier in nuclear research -
The investigation of nuclei in the energy domain of the elementary N*-resonances (i.e. for 200 MeV < Eexc < 2 GeV) opens up a new and important domain of nuclear research for essentially two reasons: (i) the quark structure of the nuclear constituent, the nucleon, leads to new nuclear phenomena; their investigation appears to be of fundamental importance for the understanding of complex hadronic systems; (ii) the nucleus can be used as a unique laboratory to test QCD in the nonasymptotic region where perturbative approaches fail. This is of particular interest, e.g. for the confinement problem. — Some specific aspects of subnuclear research are discussed in connection with the analysis of recent experiments and, in particular, in view of a possible strategy for a systematic investigation of nuclear quark excitations.
118736183
Unified Description of Pion-Photo-Production and Elastic Pion Scattering on the Deuteron in the Isobar-Doorway Model
It has been recognized recently1 that the strong dominance of the Δ(1236) isobar in nuclear reactions at medium energies advocates an explicit treatment of this degree of freedom in nuclei (in contrast to its implicit incorporation in an optical model description). Such a model, phrased commonly as isobar doorway or A* model1 has two particularly interesting features, (i) it forms a natural basis for a unified description of different isobar dominated scattering processes; (ii) it offers a more or less direct test of the isobar self energy in nuclei or, equivalently, of the ΔN interaction. An ideal testing ground for such a model seems to be deuteron: with all many-body complications being absent, predictions for scattering reactions on the deuteron should reflect and in this way allow direct investigation of the various ingredients of the model.
13703277
COLLECTIVE TREATMENT OF THE GIANT RESONANCES IN SPHERICAL NUCLEI.
In a collective treatment the energies of the giant resonances are given by the boundary conditions at the nuclear surface, which is subject to vibration in spherical nuclei. The general form of the coupling between these two collective motions is given by angular-momentum and parity conservation. The coupling constants are completely determined within the hydrodynamical model. In the present treatment the influence of the surface vibrations on the total photon-absorption cross section is calculated. It turns out that in most of the spherical nuclei this interaction leads to a pronounced structure in the cross section. The agreement with the experiments in medium-heavy nuclei is striking; many of the experimental characteristics are reproduced by the present calculations. In some nuclei, however, there seem to be indications of single-particle excitations which are not yet contained in this work.
120855950
Pionic and electromagnetic excitation of A* resonances
The nuclear excitation spectrum in the Delta (3,3) energy range is studied by comparing elastic pion scattering with coherent neutral pion photoproduction. The corresponding multipole excitation strength distributions are found to be quite different. This emphasises the role of the electromagnetic excitations of nuclei for the investigation of the A* resonances which is complementary to their mesonic excitation. Results are presented for 12C( gamma , pi 0) 12C(GS); they are compared with those of the phenomenological isobar doorway model and of DWIA calculations.
55650213
A Dyson–Schwinger study of the four-gluon vertex
We present a self-consistent calculation of the four-gluon vertex of Landau gauge Yang–Mills theory from a truncated Dyson–Schwinger equation. The equation contains the leading diagrams in the ultraviolet and is solved using as the only input results for lower Green functions from previous Dyson–Schwinger calculations that are in good agreement with lattice data. All quantities are therefore fixed and no higher Green functions enter within this truncation. Our self-consistent solution resolves the full momentum dependence of the vertex but is limited to the tree-level tensor structure at the moment. Calculations of selected dressing functions for other tensor structures from this solution are used to exemplify that they are suppressed compared to the tree-level structure except for possible logarithmic enhancements in the deep infrared. Our results furthermore allow one to extract a qualitative fit for the vertex and a running coupling.
123537479
Report on Stanford Superconductive Monopole Detectors
Since January, 1983 we have been operating a three loop superconducting detector with a signal to noise ratio of 100 for the direct detection of Dirac magnetic charges.1 Its sensing area averaged over solid angle is nearly 500 cm2 for double coincidence events. To date, the data contain no candidate events and set an upper flux limit of 2 × 10−11 cm−2 s−1 sr−1 at 90% C.L., 70 times lower than that suggested by the single candidate event2 seen on the prototype single loop detector. If supermassive magnetic monopoles exist they are rare and the need for cost-efficient larger area superconductive detectors is evident if we are to push forward a definitive search in the cosmic rays. Superconducting loop detectors can be constructed with 1 to 10 m2 planar areas coupled to a single SQUID while achieving a signal to noise ratio of 10 for the detection of a Dirac magnetic charge. A 100 m2 sensing area array of such detectors, which would reach the Parker flux bound in one year of operation, can be built at a cost comparable to that of typical high energy experiments. It remains quite possible that a monopole particle flux significantly higher than the Parker bound exists within our galaxy. In this paper the most recent results from low noise operation of the three loop detector are presented. Also discussed are our plans to build a larger fixed loop detector with a sensing area of 1.5 m2. It is designed as a prototype for a future yet larger 100 m2 array.
15971982
Limits on spin-dependent WIMP-nucleon interactions from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) is an experiment to detect weakly interacting massive particles (WIMPs), which may constitute the universe’s dark matter, based on their interactions with Ge and Si nuclei. We report the results of an analysis of data from the first two runs of CDMS at the Soudan Underground Laboratory in terms of spin-dependent WIMP-nucleon interactions on 73 Ge and 29 Si. These data exclude new regions of WIMP parameter space, including regions relevant to spin-dependent interpretations of the annual modulation signal reported by the DAMA/NaI experiment.
43394178
Algorithmic derivation of Dyson-Schwinger equations
Abstract We present an algorithm for the derivation of Dyson–Schwinger equations of general theories that is suitable for an implementation within a symbolic programming language. Moreover, we introduce the Mathematica package DoDSE 1 which provides such an implementation. It derives the Dyson–Schwinger equations graphically once the interactions of the theory are specified. A few examples for the application of both the algorithm and the DoDSE package are provided. Program summary Program title: DoDSE Catalogue identifier: AECT_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AECT_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 105 874 No. of bytes in distributed program, including test data, etc.: 262 446 Distribution format: tar.gz Programming language: Mathematica 6 and higher Computer: all on which Mathematica is available Operating system: all on which Mathematica is available Classification: 11.1, 11.4, 11.5, 11.6 Nature of problem: Derivation of Dyson–Schwinger equations for a theory with given interactions. Solution method: Implementation of an algorithm for the derivation of Dyson–Schwinger equations. Unusual features: The results can be plotted as Feynman diagrams in Mathematica. Running time: Less than a second to minutes for Dyson–Schwinger equations of higher vertex functions.
117986736
On two- and three-point functions of Landau gauge Yang-Mills theory
We present results for the gluon and ghost propagators and the ghost-gluon vertex obtained from Dyson-Schwinger equations. In the zero temperature case we elaborate on the role of the three-gluon vertex and discuss a model that can capture its qualitative features like its anomalous dimensions and a zero crossing of the dressing function. Our results compare well with lattice data. At non-zero temperature we calculated the ghost propagator which agrees rather well with lattice results already within our simple truncation. These results are used to obtain the temperature dependence of the ghost-gluon vertex. We also explain why the ghost propagator does not react to the phase transition despite its direct coupling to the chromoelectric gluon.