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On the role of unitarity in statistical theories of nuclear reactions
ANNALS
OF PHYSICS
Abstracts
102, 344-345 (1976)
of Papers
to Appear
in Future
Issues
Experimental Aspects of Synchrotron-cerenkov Radiation. T. ERBER AND D. WHITE, Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616; WU-YANG TSAI, Department of Physics, University of California at Los Angeles, California 90024; H. G. LATAL, Institut fur theoretische Physik, Universitlt Graz, A-8010 Graz, Austria. Variousfeatures of synchrotron-Cerenkovradiationare illustrated in thecontextof the following situations: (1) the passage of high-energy electrons through gases, liquids, solids, and plasmas in the presence of magnetic fields; (2) the suppression of synchrotron X rays from high-energy electrons in the earth’s atmosphere and extraterrestrial environs; (3) the detection of the real part of the Delbrtick scattering amplitude; (4) vacuum polarization effects on radiation by ultrahigh-energy electrons in intense magnetic fields; (5) synchrotron-Cerenkov radiation by charged particles heavier than electrons.
On the Role of Unitarity in Statistical Theories of Nuclear Reactions. A. K. KERMAN, Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; A. SEVGEN, Department of Physics, Bogazici University, Bebek, Istanbul, Turkey. It is argued that the approximate statistical S-matrix with energy-independent background S-matrix, residues, and poles and with fixed dimensions need not satisfy analytic unitarity but should in general obey the average unitarity condition. The freedom obtained by relaxing analytic unitarity allows a representation where level-level correlations are not present. Different approaches to statistical theories of nuclear reactions employing the pole decomposition of the S-matrix are compared. It is seen that any such approach is characterized by the assumed form of two (matrix) parameters. A model is developed which gives the expected results for the compound cross sections in the limits of strong absorption, and weak absorption with statistically equivalent channels and interpolates between the two extremes. The model depends, however, on the parameter rr/D. The possibility of extracting the value of this parameter from experimental data for the variance of cross sections is also investigated.
The Collision of Plane Waves in General Relativity. J. B. GRIFFITHS, Department of Mathematics, University of Technology, Loughborough, Leicestershire, LEl 1 3TU, England. A number of exact solutions of Einstein’s equations are obtained, which describe the collision and subsequent interaction of two plane parallel waves. Gravitational waves, null electromagnetic fields, and neutrino fields are all considered with collisions between any two types. It is shown that two such waves mutually focus each other with the focus usually appearing as a singularity in space-time. Further conclusions are made regarding the qualitative nature of the interactions, and it is argued that these also apply in more realistic physical situations. 344 Copyright 0 1976 by Academic Press, Inc. AU rights of reproduction in any form reserved.
OF PHYSICS
Abstracts
102, 344-345 (1976)
of Papers
to Appear
in Future
Issues
Experimental Aspects of Synchrotron-cerenkov Radiation. T. ERBER AND D. WHITE, Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616; WU-YANG TSAI, Department of Physics, University of California at Los Angeles, California 90024; H. G. LATAL, Institut fur theoretische Physik, Universitlt Graz, A-8010 Graz, Austria. Variousfeatures of synchrotron-Cerenkovradiationare illustrated in thecontextof the following situations: (1) the passage of high-energy electrons through gases, liquids, solids, and plasmas in the presence of magnetic fields; (2) the suppression of synchrotron X rays from high-energy electrons in the earth’s atmosphere and extraterrestrial environs; (3) the detection of the real part of the Delbrtick scattering amplitude; (4) vacuum polarization effects on radiation by ultrahigh-energy electrons in intense magnetic fields; (5) synchrotron-Cerenkov radiation by charged particles heavier than electrons.
On the Role of Unitarity in Statistical Theories of Nuclear Reactions. A. K. KERMAN, Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; A. SEVGEN, Department of Physics, Bogazici University, Bebek, Istanbul, Turkey. It is argued that the approximate statistical S-matrix with energy-independent background S-matrix, residues, and poles and with fixed dimensions need not satisfy analytic unitarity but should in general obey the average unitarity condition. The freedom obtained by relaxing analytic unitarity allows a representation where level-level correlations are not present. Different approaches to statistical theories of nuclear reactions employing the pole decomposition of the S-matrix are compared. It is seen that any such approach is characterized by the assumed form of two (matrix) parameters. A model is developed which gives the expected results for the compound cross sections in the limits of strong absorption, and weak absorption with statistically equivalent channels and interpolates between the two extremes. The model depends, however, on the parameter rr/D. The possibility of extracting the value of this parameter from experimental data for the variance of cross sections is also investigated.
The Collision of Plane Waves in General Relativity. J. B. GRIFFITHS, Department of Mathematics, University of Technology, Loughborough, Leicestershire, LEl 1 3TU, England. A number of exact solutions of Einstein’s equations are obtained, which describe the collision and subsequent interaction of two plane parallel waves. Gravitational waves, null electromagnetic fields, and neutrino fields are all considered with collisions between any two types. It is shown that two such waves mutually focus each other with the focus usually appearing as a singularity in space-time. Further conclusions are made regarding the qualitative nature of the interactions, and it is argued that these also apply in more realistic physical situations. 344 Copyright 0 1976 by Academic Press, Inc. AU rights of reproduction in any form reserved.