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AbstractAbstract

[en] We use the worldline representation of field theory together with a variational approximation to determine the lowest bound state in the scalar Wick-Cutkosky model where two equal-mass constituents interact via the exchange of mesons. Self-energy and vertex corrections are included approximately in a consistent way as well as crossed diagrams. Only vacuum-polarization effects of the heavy particles are neglected. In a path-integral description of an appropriate current-current correlator an effective, retarded action is obtained by integrating out the meson field. As in the polaron problem we employ a quadratic trial action with variational functions to describe retardation and binding effects through multiple meson exchange. The variational equations for these functions are derived, discussed qualitatively and solved numerically. We compare our results with the ones from traditional approaches based on the Bethe-Salpeter equation and find an enhanced binding contrary to some claims in the literature. For the weak coupling this is worked out analytically and compared with results from effective field theories. However, the well-known instability of the model, which usually is ignored, now appears at smaller coupling constants than in the one-body case and even when self-energy and vertex corrections are turned off. This induced instability is investigated analytically and the width of the bound state above the critical coupling is estimated. (author)

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AbstractAbstract

[en] A method using an expansion of the four-body Yakubovsky wave function on the basis of the Faddeev-equation solutions for the two-cluster sub-Hamiltonian eigenfunctions is exploited for computations of low-energy scattering parameters in four nucleon systems. Results of calculations of low-energy scattering parameters in n-

^{3}H, n-^{3}He, singlet and triplet p-3^{H}, p-^{3}He elastic scattering lengths are presented. Refs. 14, tabs. 3 (nevyjel)Primary Subject

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16. European conference on few-body problems in physics; Autrans (France); 1-6 Jun 1998; Title of the Supplementum: Few-body problems in physics '98

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Journal Article

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Conference

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 37-40

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BARYONS, BASIC INTERACTIONS, BETA DECAY RADIOISOTOPES, BETA-MINUS DECAY RADIOISOTOPES, CALCULATION METHODS, DIMENSIONS, ELASTIC SCATTERING, ELECTROMAGNETIC INTERACTIONS, ELEMENTARY PARTICLES, EVEN-ODD NUCLEI, FERMIONS, FUNCTIONS, HADRONS, HELIUM ISOTOPES, HYDROGEN ISOTOPES, INTERACTIONS, ISOTOPES, LENGTH, LIGHT NUCLEI, MANY-BODY PROBLEM, NUCLEI, NUCLEONS, ODD-EVEN NUCLEI, RADIOISOTOPES, SCATTERING, STABLE ISOTOPES, VARIATIONAL METHODS, YEARS LIVING RADIOISOTOPES

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AbstractAbstract

[en] Algorithm, based on explicit representations for the analytic continuation of Faddeev components of the three-body T-matrix in unphysical energy sheets, is employed to study the mechanism of disappearance and formation of the Efimov levels of the helium

^{4}He trimer. Refs. 12, figs. 2, tabs. 2 (author)Primary Subject

Source

16. European conference on few-body problems in physics; Autrans (France); 1-6 Jun 1998; Title of the Supplementum: Few-body problems in physics '98

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Journal Article

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Conference

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 75-84

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AbstractAbstract

[en] The collisional metastability of antiprotonic atomcules He

^{+}- p in pure helium is discussed in the framework of a classical trajectory approach for three slow nuclei (αp - α) moving in an ab initio Born-Oppenheimer electronic potential. Our results support the destruction of the n > 41 states during the thermalization stage, as well as the strong depopulation of the elliptic states adjacent to Auger-dominated short-lived levels. Refs. 9, figs. 4 (author)Primary Subject

Source

16. European conference on few-body problems in physics; Autrans (France); 1-6 Jun 1998; Title of the Supplementum: Few-body problems in physics '98

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Journal Article

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Conference

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 211-214

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ANTIBARYONS, ANTIMATTER, ANTINUCLEI, ANTINUCLEONS, ANTIPARTICLES, APPROXIMATIONS, ATOMS, BARYONS, CALCULATION METHODS, CHARGED PARTICLES, ELEMENTARY PARTICLES, ELEMENTS, ENERGY LEVELS, EXCITED STATES, FERMIONS, FLUIDS, GASES, HADRONS, IONIZING RADIATIONS, IONS, LEPTONS, MANY-BODY PROBLEM, MATTER, NONMETALS, NUCLEI, NUCLEONS, PROTONS, RADIATIONS, RARE GASES

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AbstractAbstract

[en] A new scheme of physical processes leading to the nuclear fusion reaction d(

^{3}He,^{4}He)p catalyzed by a negatively charged muon (μ^{-}) is presented. It is shown that the observable rate and yield of the nuclear reaction depend on a chain of ion-molecular reactions in which the dμ^{3}He-molecule participates. New calculations of the nuclear fusion rates in the dμ^{3}He-molecule are presented. Refs. 14, fig. 1 (author)Primary Subject

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 227-230

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AbstractAbstract

[en] Since the first attempts to calculate the helium ground state in the early days of Bohr-Sommerfeld quantization two-electron atoms have posed a series of unexpected challenges to theoretical physics. Despite the seemingly simple problem of three charged particles with known interactions it took more than half a century after quantum mechanics was established to describe spectra of two-electron atoms satisfactorily. The evolution of the understanding of correlated two-electron dynamics and its importance for doubly excited resonance states is sketched in this overview by contrasting a forgotten idea from the old days with recent theoretical concepts and new challenges. Refs. 26, figs. 4 (author)

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 253-262

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Hegerfeldt, G.C.; Koehler, T., E-mail: hegerf@theorie.physik.uni-goettingen.de, E-mail: koehler@theorie.physik.uni-goettingen.de

AbstractAbstract

[en] We use few-body methods to investigate the diffraction of weakly bound systems by a transmission grating. For helium dimers, He

_{2}, we obtain explicit expressions for the transition amplitude in the elastic channel. Refs. 15, figs. 5 (author)Primary Subject

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 263-272

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Alt, E.O.; Mukhamedzhanov, A.M.; Sattarov, A.I., E-mail: alt@dipmza.physik.uni-mainz.de, E-mail: akram@comp.tamu.edu, E-mail: dior@phyacc.tamu.edu

Funding organisation: Department of Education (United States); Deutsche Forschungsgemeinschaft (Germany)

Funding organisation: Department of Education (United States); Deutsche Forschungsgemeinschaft (Germany)

AbstractAbstract

[en] We report on the first reliable numerical results for proton-deuteron elastic scattering observables for energies above the deuteron breakup threshold, for the Paris potential. The calculations have been performed within the screening and renormalisation approach. The theoretical results are compared with recent experimental data. Refs. 12, fig. 1 (author)

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16. European conference on few-body problems in physics; Autrans (France); 1-6 Jun 1998; DE-FG05-93-ER40773; PROJECT 436 USB-113-1-0; Title of the Supplementum: Few-body problems in physics '98

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Journal Article

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Conference; Numerical Data

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 331-334

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AbstractAbstract

[en] Pion-pion scattering is investigated in the framework of the Resonating Group Method (RGM). The wave function of an isolated pion, described as a quark-antiquark system interacting through a potential composed of a central and a spin-spin part, is determined using the spinless Salpeter equation. Given these ingredients the kernel of the integro-differential equation governing the relative motion of the colliding pions is calculated using relativistic kinematics. The corresponding S- and D-wave pion-pion phase shifts and their Galilean counterparts are compared with experiment. Refs. 3 (author)

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 471-474

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AbstractAbstract

[en] In quantum mechanics the principle of relativity is guaranteed by unitary operators being associated with inhomogeneous Lorentz transformations ensuring that quantum mechanical expectation values remain unchanged. In field theory the ten generators of inhomogeneous Lorentz transformations can be derived from a scalar Lagrangian density describing the physical system of interest. They obey the well known Poincare Lie algebra. For interacting systems some of the generators become operators allowing for particle production or annihilation so that the generators act on the full Fock space. However, given a field theory on the whole Fock space we prove that it is possible to construct generators acting on a subspace with a finite number of particles by one and the same unitary transformation of all generators leaving the Poincare algebra valid. In this manner it is in principle possible to derive a relativistically invariant theory of interacting particles on a Hilbert space with a finite number of particles from a field theoretical Lagrangian. Refs. 3 (author)

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Few-Body Systems. Supplementum; ISSN 0177-8811; ; v. 10; p. 483-486

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