386 research outputs found

    Large N WZW Field Theory Of N=2 Strings

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    We explore the quantum properties of self-dual gravity formulated as a large NN two-dimensional WZW sigma model. Using a non-trivial classical background, we show that a (2,2)(2,2) space-time is generated. The theory contains an infinite series of higher point vertices. At tree level we show that, in spite of the presence of higher than cubic vertices, the on-shell 4 and higher point functions vanish, indicating that this model is related with the field theory of closed N=2 strings. We examine the one-loop on-shell 3-point amplitude and show that it is ultra-violet finite.Comment: This is the final version. By editorial mistake at Phys.Lett.B an older version was published in prin

    Status of Underground Radioactivity Measurements in HADES

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    The IRMM (Institute for Reference materials and Measurements) performs ultra low-level gamma-ray spectrometry at a depth of 225 m in the underground laboratory HADES. The facility currently houses 7 HPGe-detectors that are built and shielded using specially selected radiopure materials. The sandclay overburden of about 500 m water equivalent assures a muon flux reduction factor of about 5000, with subsequent reduction of the background of the detectors, which makes it possible to obtain detection limits close to 100 ”Bq for certain radionuclides. This paper describes the aim of the IRMM activities in the HADES laboratory, the equipment and the measurement program and gives examples of radiopurity measurements carried out in order to develop better low-level measurements.JRC.DG.D.5-Nuclear physic

    Coded Aperture and Compton Imaging for the Development of 225^{225}Ac-based Radiopharmaceuticals

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    Targeted alpha-particle therapy (TAT) has great promise as a cancer treatment. Arguably the most promising TAT radionuclide that has been proposed is 225^{225}Ac. The development of 225^{225}Ac-based radiopharmaceuticals has been hampered due to the lack of effective means to study the daughter redistribution of these agents in small animals at the preclinical stage. The ability to directly image the daughters, namely 221^{221}Fr and 213^{213}Bi, via their gamma-ray emissions would be a boon for preclinical studies. That said, conventional medical imaging modalities, including single photon emission computed tomography (SPECT) based on pinhole collimation, cannot be employed due to sensitivity limitations. As an alternative, we propose the use of both coded aperture and Compton imaging with the former modality suited to the 218-keV gamma-ray emission of 221^{221}Fr and the latter suited to the 440-keV gamma-ray emission of 213^{213}Bi. This work includes coded aperture images of 221^{221}Fr and Compton images of 213^{213}Bi in tumor-bearing mice injected with 225^{225}Ac-based radiopharmaceuticals. These results are the first demonstration of visualizing and quantifying the 225^{225}Ac daughters in small animals via coded aperture and Compton imaging and serve as a stepping stone for future radiopharmaceutical studies

    Evaluation Of Glueball Masses From Supergravity

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    In the framework of the conjectured duality relation between large NN gauge theory and supergravity the spectra of masses in large NN gauge theory can be determined by solving certain eigenvalue problems in supergravity. In this paper we study the eigenmass problem given by Witten as a possible approximation for masses in QCD without supersymmetry. We place a particular emphasis on the treatment of the horizon and related boundary conditions. We construct exact expressions for the analytic expansions of the wave functions both at the horizon and at infinity and show that requiring smoothness at the horizon and normalizability gives a well defined eigenvalue problem. We show for example that there are no smooth solutions with vanishing derivative at the horizon. The mass eigenvalues up to m2=1000m^{2}=1000 corresponding to smooth normalizable wave functions are presented. We comment on the relation of our work with the results found in a recent paper by Cs\'aki et al., hep-th/9806021, which addresses the same problem.Comment: 20 pages,Latex,3 figs,psfig.tex, added refs., minor change

    Evolution of Plasma Composition in an Eruptive Flux Rope

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    Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level

    Large N Field Theory of N=2 Strings and Self-Dual Gravity

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    We review some aspects of the construction of self-dual gravity and the associated field theory of N=2{\cal N}=2 strings in terms of two-dimensional sigma models at large NN. The theory is defined through a large NN Wess-Zumino-Witten model in a nontrivial background and in a particular double scaling limit. We examine the canonical structure of the theory and describe an infinite-dimensional Poisson algebra of currents.Comment: To appear in the special issue of the Journ. of Chaos, Solitons and Fractals, 24 page
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