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  • 1.
    Elander, Nils O
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rakityansky, Sergei
    Univ Pretoria, Dept Phys, ZA-002 Pretoria, South Africa .
    Resonances and Their Relations to Spectral Densities and Scattering Cross Sections in the Schrodinger Formulation2013Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 54, nr 5-6, s. 685-695Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The concept of resonances for a two-body single and many channel Schrodinger problem is discussed with respect to the Titchmarsh-Weyl theory. It is argued that the contributions from the entire set of resonances together with the free particle spectral density build the entire spectrum. The implication of this statement on the influence of resonances on a two-body scattering cross section is discussed. It is described how the residues of the S-matrix at a complex resonance energy, i.e. two complex numbers, is used to define its contribution to the cross section. The limitations of the Breit-Wigner approximation is discussed.

  • 2.
    Elander, Nils
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Shilyaeva, Ksenia
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ostrovsky, Valentin
    V. Fock Institute of Physics, St. Petersburg State University.
    Yarevsky, Evgeny
    St. Petersburg State University.
    Rakityanski, Sergey
    University of South Africa.
    Tools for assigning resonance structures in collisions of few body quantum systems2006Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 38, nr 2-4, s. 109-114Artikel i tidskrift (Refereegranskat)
  • 3.
    Elander, Nils
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Volkov, Mikhail
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Åsa
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stenrup, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mezei, J. Zsolt
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Yarevsky, Evgeny
    Yakolev, Sergey
    Quantum Scattering with the Driven Schrödinger Approachand Complex Scaling2009Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 45, nr 2-4, s. 197-201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum scattering calculations of two and three-body systems with Coulomb interaction using thedriven Schrödinger equation combined with exterior complex scaling are discussed. A rigorous formulationfor two-body scattering is reported, and its generalization to three-body scattering is considered.

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  • 4.
    Kurasov, Pavel
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    How to model p-scattering using point interactions and related problems2009Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411Artikel i tidskrift (Refereegranskat)
  • 5. Rakityansky, S. A.
    et al.
    Elander, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Analytic Structure and Power-Series Expansion of the Jost Matrix2013Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 54, nr 5-6, s. 673-683Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the Jost-matrix that describes the multi-channel scattering, the momentum dependencies at all the branching points on the Riemann surface are factorized analytically. The remaining single-valued matrix functions of the energy are expanded in the power-series near an arbitrary point in the complex energy plane. A systematic and accurate procedure has been developed for calculating the expansion coefficients. This makes it possible to obtain an analytic expression for the Jost-matrix (and therefore for the S-matrix) near an arbitrary point on the Riemann surface (within the domain of its analyticity) and thus to locate the resonant states as the S-matrix poles. This approach generalizes the standard effective-range expansion that now can be done not only near the threshold, but practically near an arbitrary point on the Riemann surface of the energy. Alternatively, The semi-analytic (power-series) expression of the Jost matrix can be used for extracting the resonance parameters from experimental data. In doing this, the expansion coefficients can be treated as fitting parameters to reproduce experimental data on the real axis (near a chosen center of expansion E (0)) and then the resulting semi-analytic matrix S(E) can be used at the nearby complex energies for locating the resonances. Similarly to the expansion procedure in the three-dimensional space, we obtain the expansion for the Jost function describing a quantum system in the space of two dimensions (motion on a plane), where the logarithmic branching point is present.

  • 6. Yamashita, Takuma
    et al.
    Kino, Yasushi
    Hiyama, Emiko
    Jonsell, Svante
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Froelich, Piotr
    Four-body Calculation of Inelastic Scattering Cross Sections of Positronium-Antihydrogen Collision2021Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 62, nr 4, artikel-id 81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We overview our recent calculations of scattering cross sections of positronium–antihydrogen collisions. We discuss the cross sections calculated in the vicinity of the four-body resonances of H¯Ps and above the energy threshold for the formation of the antihydrogen positive ions (H¯+). In the former energy region where a Rydberg series of resonances dominated by the H¯+-e− interaction appears, we show a good agreement between the resonant profiles in the cross sections and the resonance energies calculated by the complex coordinate rotation method. H¯+ production cross sections near the threshold energy are reported for the positronium being initially in the (nl) states with n≤3, together with all competing elastic/inelastic cross sections. Comparison of our results with the latest continuum distorted wave final state calculation is presented. A qualitative discrepancy concerning the dependence of cross sections on the angular momentum of Ps is indicated.

  • 7. Yarevsky, E.
    et al.
    Yakovlev, S. L.
    Elander, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Volkov, M. V.
    On the Scattering of the Electron off the Hydrogen Atom and the Helium Ion Below and Above the Ionization Threshold: Temkin-Poet Model2014Ingår i: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 55, nr 8-10, s. 1057-1058Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We generalize here the splitting approach to the long range (Coulomb) interaction for the three body scattering problem. With this approach, the exterior complex rotation technique can be applied for systems with asymptotic Coulomb interaction. We illustrate the method with calculations of the electron scattering on the hydrogen atom and positive helium ion in the frame of the Temkin-Poet model.

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