| 1. |
- Armstrong, Jeremy, et al.
(författare)
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Interaction Blockade and Pairing in Two-Dimensional Finite Fermion Systems
- 2009
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Ingår i: Few-body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 45:2-4, s. 219-222
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Konferensbidrag (refereegranskat)abstract
- The properties of two-component fermionic quantum systems in two dimensions, such as they nowadays may be realized with cold atoms in traps, are studied within the pairing model adapted from nuclear physics. We compare the results with those of a full numerical diagonalization of the many-body Hamiltonian. The chemical potential differences, excitation energies and angular momentum spectra show that when the zero-range attractive interaction is varied in strength, strong odd-even effects, gaps and shell structure emerge.
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| 2. |
- Cremon, Jonas
(författare)
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Test of a Jastrow-type Wavefunction for a Trapped Few-body System in One Dimension
- 2012
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 53:3-4, s. 267-269
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Tidskriftsartikel (refereegranskat)abstract
- For a system with interacting quantum mechanical particles in a one-dimensional harmonic oscillator, a trial wavefunction with simple structure based on the solution of the corresponding two-particle system is suggested and tested numerically.With the inclusion of a scaling parameter for the distance between particles, at least for the very small systems tested here the ansatz gives a very good estimate of the ground state energy, with the error being of the order of 1 % of the gap to the first excited state.
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| 3. |
- Cremon, Jonas, et al.
(författare)
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Vortices in small Bose or Fermi systems with repulsive interactions
- 2008
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 43:1-4, s. 161-166
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Konferensbidrag (refereegranskat)abstract
- For rotating Bose-Einstein condensates, the occurrence of vortices has been much discussed in the Gross-Pitaevskii approach. Here, we study vortex formation in finite systems with few particles for weak and repulsive two-body interactions, by numerical diagonalization. Vortex formation is surprisingly similar for both (spinless) bosonic and fermionic particles. Breaking the rotational invariance of the Hamiltonian of the system reveals the vortex patterns. A transformation from a many-fermion to a many-boson state is proposed.
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| 4. |
- Deltuva, A., et al.
(författare)
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Universality in Four-Body Scattering
- 2011
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 51:2-4, s. 235-247
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Tidskriftsartikel (refereegranskat)abstract
- The four-body system is studied in the limit of large two-body scattering length by solving momentum-space integral equations for the transition operators or, alternatively, configuration-space equations for wave function. A number of universal results for atom-trimer and dimer-dimer scattering observables are found. We furthermore address the question whether the universal four-body systems contain additional states besides the known two S-wave states.
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| 5. |
- Elander, Nils O, et al.
(författare)
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Resonances and Their Relations to Spectral Densities and Scattering Cross Sections in the Schrodinger Formulation
- 2013
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 54:5-6, s. 685-695
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Elander, Nils, et al.
(författare)
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Quantum Scattering with the Driven Schrödinger Approachand Complex Scaling
- 2009
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Ingår i: Few-body systems. - Heidelberg : Springer Verlag. - 0177-7963 .- 1432-5411. ; 45:2-4, s. 197-201
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 7. |
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| 8. |
- Feldman, G., et al.
(författare)
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Compton scattering from deuterium and the polarizabilities of the neutron
- 2008
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 44:1-4, s. 325-328
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Konferensbidrag (refereegranskat)abstract
- A new program of Compton scattering on deuterium is under way at the tagged-photon facility at MAX-Lab in Lund, Sweden. We will measure differential cross sections between 60A degrees and 150A degrees over the photon energy range 60-115 MeV in 5 MeV steps, with the ultimate goal of obtaining new precision information on the electric and magnetic polarizabilities of the neutron.
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| 9. |
- Floerchinger, Stefan, et al.
(författare)
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Efimov Physics from the Functional Renormalization Group
- 2011
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 51:2-4, SI, s. 153-180
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Tidskriftsartikel (refereegranskat)abstract
- Few-body physics related to the Efimov effect is discussed using the functional renormalization group method. After a short review of renormalization in its modern formulation we apply this formalism to the description of scattering and bound states in few-body systems of identical bosons and distinguishable fermions with two and three components. The Efimov effect leads to a limit cycle in the renormalization group flow. Recently measured three-body loss rates in an ultracold Fermi gas of Li-6 atoms are explained within this framework. We also discuss briefly the relation to the many-body physics of the BCS-BEC crossover for two-component fermions and the formation of a trion phase for the case of three species.
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| 10. |
- Forssen, Christian, 1974, et al.
(författare)
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Strongly Interacting Few-Fermion Systems in a Trap
- 2015
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 56:11-12, s. 837-844
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Tidskriftsartikel (refereegranskat)abstract
- Few- and many-fermion systems on the verge of stability, and consisting of strongly interacting particles, appear in many areas of physics. The theoretical modeling of such systems is a very difficult problem. In this work we present a theoretical framework that is based on the rigged Hilbert space formulation. The few-body problem is solved by exact diagonalization using a basis in which bound, resonant, and non-resonant scattering states are included on an equal footing. Current experiments with ultracold atoms offer a fascinating opportunity to study universal properties of few-body systems with a high degree of control over parameters such as the external trap geometry, the number of particles, and even the interaction strength. In particular, particles can be allowed to tunnel out of the trap by applying a magnetic-field gradient that effectively lowers the potential barrier. The result is a tunable open quantum system that allows detailed studies of the tunneling mechanism. In this Paper we introduce our method and present results for the decay rate of two distinguishable fermions in a one-dimensional trap as a function of the interaction strength. In particular, we present for the first time several technical and numerical details of our approach, recently published in Lundmark et al. (Phys Rev A 91:041601, 2015). We also show results from a careful analysis of the numerical convergence.
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| 11. |
- Forssen, Christian, 1974, et al.
(författare)
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The Ab Initio No-core Shell Model
- 2009
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 45:2, s. 111-
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Konferensbidrag (refereegranskat)abstract
- This contribution reviews a number of applications of the ab initio no-core shell model (NCSM) within nuclear physics and beyond. We will highlight a nuclear-structure study of the A = 12 isobar using a chiral NN + 3NF interaction. In the spirit of this workshop we will also mention the new development of the NCSM formalism to describe open channels and to approach the problem of nuclear reactions. Finally, we will illustrate the universality of the many-body problem by presenting the recent adaptation of the NCSM effective-interaction approach to study the many-boson problem in an external trapping potential with short-range interactions.This article is based on the presentation by C. Forssén at the Fifth Workshop on Critical Stability, Erice, Sicily.
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| 12. |
- Forssen, Christian, 1974, et al.
(författare)
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The ab initio No-Core Shell Model and Light Nuclei
- 2011
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 49:1-4, s. 11-18
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Tidskriftsartikel (refereegranskat)abstract
- The ab initio no-core shell model (NCSM) is a well-established theoretical framework aimed at an exact description of nuclear structure starting from high-precision interactions between the nucleons. In the NCSM we consider a system of A point-like, non-relativistic nucleons that interact by realistic inter-nucleon interactions. We consider two-nucleon interactions that reproduce nucleon-nucleon phase shifts with high precision, typically up to 350 MeV lab energy. We can also include three-nucleon interactions with terms, e.g., related to two-pion exchanges with an intermediate delta excitation. Both semi-phenomenological potentials, based on meson-exchange models, as well as modern chiral interactions can be considered. The performance of the NCSM within nuclear physics will be exemplified by showing results from studies of light nuclei. Major challenges in the future development of the method will be outlined.
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| 13. |
- Froelich, Piotr, et al.
(författare)
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Hydrogen : Antihydrogen Molecule and its Properties
- 2004
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 34:1-3, s. 63-72
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Tidskriftsartikel (refereegranskat)abstract
- The metastability of the four-body system is discussed from the point of view of radiative rearrangement collisions of the hydrogen and antihydrogen. Such collisions lead to the formation of an intermediate molecular state which further decays into positronium and protonium or is destroyed via annihilation. We present calculations of the lifetime of the system and the branching ratios for Coulombic decay and annihilation.
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| 14. |
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| 15. |
- Gorini, G., et al.
(författare)
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Nuclear scattering effects on the neutron emission in fusion plasmas
- 2008
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 44:1-4, s. 57-60
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Tidskriftsartikel (refereegranskat)abstract
- Ion reactions and elastic scatterings in fusion plasmas of H and He nuclides are discussed as they can be observed in the neutron emission spectrum (NES). New calculations are presented on radio-frequency driven multi-step processes in (HeD)-He-3 plasmas involving knock-on scattering whose relative importance is discussed besides use for new plasma studies.
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| 16. |
- Huang, S.W., et al.
(författare)
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Experimental Study of 4n by Directly Detecting the Decay Neutrons
- 2021
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- The tetraneutron has attracted the attention of nuclear physicists during the past decades, but there is still no unambiguous confirmation of its existence or non-existence. A new experiment based on 8He(p, 2p)7H{t+4n} reaction, with direct detection of the four neutrons, has been carried out at RIBF, which can hopefully help to draw a definite conclusion on the tetraneutron system. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
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| 17. |
- Id Betan, Rodolfo M, et al.
(författare)
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Two-particle resonances in the complex energy plane
- 2004
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 34:1-3, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- An evaluation of two-particle resonances in the complex energy plane is presented. The representation used in the method consists of bound and antibound single-particle states, Gamow resonances and scattering waves on the complex energy plane. Within this representation the structure of halo nuclei is studied.
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| 18. |
- Ilderton, Anton
(författare)
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Lightfront DHW Functions and Strong Field QED
- 2012
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Ingår i: Few-body systems. - Wien : Springer. - 0177-7963 .- 1432-5411. ; 52:3-4, s. 431-436
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Tidskriftsartikel (refereegranskat)abstract
- We investigate strong-field effects in QED using a phase space approach based on the Dirac-Heisenberg-Wiger function. We calculate the electron-positron DHW function in a null (laser) field background exactly, using lightfront field theory. The DHW function exhibits the distinct features of strong-field QED: in particular we explicitly identify the effective fermion mass for arbitrary temporal pulse profiles.
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| 19. |
- Ilderton, Antony, 1978
(författare)
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Lightfront QED and Intense Field Physics
- 2014
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 55:5-7, s. 493-499
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Tidskriftsartikel (refereegranskat)abstract
- We briefly review the particular relevance of lightfront quantisation to QED in external fields modelling intense lasers.
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| 20. |
- Kurasov, Pavel
(författare)
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How to Model p-Scattering Using Point Interactions and Related Problems
- 2009
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Ingår i: Few-body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 45:2-4, s. 187-190
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Konferensbidrag (refereegranskat)abstract
- A new type of point interactions for the Laplacian in R-3 is constructed generalizing classical Fermi pseudopotential. This model leads to a new resolvent formula and a non-trivial scattering matrix in p-channel.
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| 21. |
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| 22. |
- Kuros-Zolnierczuk, J., et al.
(författare)
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Faddeev Calculations of Breakup Reactions with Realistic Experimental Constraints
- 2004
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 34, s. 259-273
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to integrate predictions from a theoretical model of a reaction with three bodies in the final state over the region of phase space covered by a given experiment. The method takes into account the true experimental acceptance, as well as variations of detector efficiency, and eliminates the need for a Monte-Carlo simulation of the detector setup. The method is applicable to kinematically complete experiments. Examples of the use of this method include sveral polarization observables in dp breakup at 270 MeV. The calculations are carried out in the Faddeev framework with the CD Bonn nucleon-nucleon interaction, with or without the inclusion of an additional three-nucleon force.
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| 23. |
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| 24. |
- Melgaard, M
(författare)
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New approach to quantum scattering near the lowest Landau threshold for a Schrodinger operator with a constant magnetic field
- 2002
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Ingår i: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 32:1-2, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- For a fixed magnetic quantum number m results on spectral properties and scattering theory are given for the three-dimensional Schrodinger operator with a constant magnetic field and an axisymmetrical electric potential V. Asymptotic expansions for the resolvent of the Hamiltonian H-m = H-om + V are deduced as the spectral parameter tends to the lowest Landau threshold E-0. In particular it is shown that E-0 can be an eigenvalue of H-m. Furthermore, asymptotic expansions of the scattering matrix associated with the pair (H-m, H-om) are derived as the energy parameter tends to E-0.
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| 25. |
- Moiseeva, A., et al.
(författare)
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Chiral Expansion of Nucleon PDF at x similar to m(pi)/M-N
- 2014
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 55:5-7, s. 389-394
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Tidskriftsartikel (refereegranskat)abstract
- Based on the chiral perturbation theory, we investigate the low-energy dynamics of nucleon parton distributions. We show that in different regions of the momentum fraction x the chiral expansion is significantly different. For nucleon parton distributions these regions are characterized by x similar to 1, x similar to m(pi)/M-N and x similar to (m(pi)/M-N)(2). We derive extended counting rules for each region and obtain model-independent results for the nucleon parton distributions down to x greater than or similar to m(pi)(2)/M-N(2) approximate to 10(-2).
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