| 1. |
- Berggren, P., et al.
(författare)
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Impact of the strong force on the Coulombic decay of a hydrogen-antihydrogen molecule
- 2008
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 41:15, s. 155202-
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Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the meta-stable hydrogen-antihydrogen molecule in various vibrational states is calculated. The partial lifetime with respect to the proton-antiproton annihilation is obtained from complex eigenvalues which arise upon inclusion of the strong force in the adiabatic formulation of the molecular decay problem. We study the influence of the strong force, which causes annihilation, on the transition probability for decay via Coulombic rearrangement to protonium and positronium.
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| 2. |
- Stegeby, Henrik, 1979-
(författare)
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Four-Body Treatment of the Hydrogen-Antihydrogen System
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a nonadiabatic (4-body) description of the hydrogen-antihydrogen system at a nonrelativistic level. The properties of the system, the rearrangement processes and the possible existence of resonance states are investigated by using a variational method for coupled arrangement channels, the Gaussian Expansion Method, and the stabilization method.The 4-body basis set is optimized by means of prediagonalization of 2-body fragments. In paper I, a mass-scaling procedure of the Born-Oppenheimer potential is introduced for the description of the relative motion between hydrogen and antihydrogen. The nonadiabaticity of the system is investigated in paper II.
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| 3. |
- Stegeby, Henrik, 1979-
(författare)
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MATTER-ANTIMATTER INTERACTIONS : The hydrogen-antihydrogen system and antiproton-matter interactions
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ever since antiparticles were discovered their nature has been something of a mystery. They were postulated to be identical to regular particles except for having opposite charge, but this would imply that an equal amount of antiparticles and particles should have been created at the beginning of time. However, everywhere we look the Universe seems to be constituted of regular particles, giving rise to the question whether there is something else that differentiates antiparticles from regular particles, or if there is something amiss in the Standard Model of particle physics.This thesis focuses on a central system of study in this field, the hydrogen-antihydrogen system and the theory surrounding it, as well as an expansion into systems with an antiproton interacting with small molecules, bridging the fields of quantum physics and quantum chemistry.Methods expanding on the Born-Oppenheimer approximation for the interaction between the two atoms are presented. The resulting 2-body interaction potential is then used for creating a part of the basis in a non-adiabatic 4-body method in order to look for resonance states whose existence could impact cross-sections of hydrogen-antihydrogen scattering. The eigenfunctions obtained from the non-adiabatic method are used by extracting the 2-body hadronic density function and comparing it to the adiabatic wave function, for measuring the adiabaticity of the hydrogen-antihydrogen system.The antiproton-matter interaction is first investigated by a quantum dynamical approach of an antiproton scattering on molecular hydrogen, common products in high-energy collision experiments, continued by a study of the potential energy surfaces of an antiproton interacting with a range of functional groups present in the human body.
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| 4. |
- Stegeby, Henrik
(författare)
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Overview Of Antiproton Affinities For Functional Groups Relevant In Particle-Beam Cancer Therapy
- 2018
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Ingår i: Cancer Reports. - : Wiley-Blackwell. - 2573-8348. ; 1:3
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Tidskriftsartikel (refereegranskat)abstract
- Background: The recent advances in the production and storing of antiprotons inspire further research regarding using an antiproton particle beam in cancer therapy.In this work, an overview study of the chemical properties that govern the reactions between biomolecules and slowly moving antiprotons have been investigated.Aim: The motivation for the article is to grant an improved understanding of the processes involved in antiproton particle-beam cancer therapy as the antiproton comes to rest, in terms of the impact of molecular chemical properties on the antiproton annihilation site of the biomolecule.Methods and results: The potential energy surfaces for an antiproton in the vicinity of common functional groups in the human body have been calculated at the CASSCF/CASPT2 level. The energies at different antiproton distances are calculated and compared between different functional groups.A comparison of the impact on the antiproton affinity from atomic number, bond order, number of lone pairs, bond polarization due to electronegativity, and charge is presented.Conclusions: The lone pair effect and bond polarization have a relatively large impact. This implies that even on the isolated molecular level, the chemical environment governing the trajectory of an antiproton is a complex problem. The study is applicable primarily in the ultra-low energy collision regime but can also function as a starting point for quantum dynamical treatments.
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| 5. |
- Stegeby, Henrik, et al.
(författare)
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Resonance states in the hydrogen-antihydrogen system from a nonadiabatic treatment
- 2016
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:1
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Tidskriftsartikel (refereegranskat)abstract
- The quantum-mechanical four-body problem for the hydrogen-antihydrogen system has been solved by means of the variational implementation of the coupled-arrangement channel method. Wave functions have been formed using the Gaussian expansion method (GEM) in Jacobi coordinates; they explicitly include components corresponding to the rearrangement from hydrogen and antihydrogen (H + (H) over bar into protonium and positronium (Pn + Ps). We analyze the solutions belonging to the discretized spectrum of the four-body eigenvalue problem, searching for resonance states at energies just below the H-(H) over bar dissociation energy threshold by means of the stabilization method and complex scaling.
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| 6. |
- Stegeby, Henrik, 1979-, et al.
(författare)
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Two-Body Hadronic Densities From The Four-Body Wave Functions For The Hydrogen-Antihydrogen System
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The quantum-mechanical four-body problem for the hydrogen-antihydrogen system has beensolved by means of the variational implementation of the coupled-arrangement channel method.The wave functions have been formed using the Gaussian expansion method (GEM) in Jacobi co-ordinates; they explicitly include components corresponding to the rearrangement from hydrogen and antihydrogen (H + H') into Protonium and Positronium (Pn + Ps). We analyse the solutionsbelonging to the discretized spectrum of the 4-body eigenvalue problem at energies correspondingto the low energy H { Hcollisions. Two-body nuclear correlation functions are calculated from thefour-body wave functions, as to investigate the proton-antiproton motion in the region of rearrangement from H+H' to Pn+Ps. We monitor the adiabatic versus nonadiabatic behavior of the system asa function of internuclear separation and nd that outside the rearrangement region the adiabaticdescription is quite adequate. The nonadiabatic behavior signicantly in uences the nuclear motionin the rearrangement region and reduces the rate of proton-antiproton annihilation in low-energy hydrogen-antihydrogen collisions.
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| 7. |
- Stegeby, Henrik, et al.
(författare)
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Variational calculations for the hydrogen-antihydrogen system with a mass-scaled Born-Oppenheimer potential
- 2012
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Ingår i: CENTRAL EUROPEAN JOURNAL OF PHYSICS. - : Walter de Gruyter GmbH. - 1895-1082. ; 10:5, s. 1038-1053
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Tidskriftsartikel (refereegranskat)abstract
- The problem of proton-antiproton motion in the H- system is investigated by means of the variational method. We introduce a modified nuclear interaction through mass-scaling of the Born-Oppenheimer potential. This improved treatment of the interaction includes the nondivergent part of the otherwise divergent adiabatic correction and shows the correct threshold behaviour. Using this potential we calculate the vibrational energy levels with angular momentum 0 and 1 and the corresponding nuclear wave functions, as well as the S-wave scattering length. We obtain a full set of all bound states together with a large number of discretized continuum states that might be utilized in variational four-body calculations. The results of our calculations gives an indication of resonance states in the hydrogen-antihydrogen system.
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| 8. |
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