Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 42) Show all publications
Thylwe, K.-E. (2019). Discontinuous radial potentials, bound states and Dirac equations. Physica Scripta, 94(6), Article ID 065201.
Open this publication in new window or tab >>Discontinuous radial potentials, bound states and Dirac equations
2019 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 94, no 6, article id 065201Article in journal (Refereed) Published
Abstract [en]

Discontinuous, radial 'square-well' potentials of scalar and (time-component) vector types require special quantization conditions in Dirac equations transformed to second-order differential equations. Quantization conditions for positive energies are derived from first-order and second-order differential equations using amplitude-phase methods. Analytic condition for no orbital angular momentum of the large spinor component is obtained. Numerical applications relevant to independent-nucleon shell models illustrate level shifts due to shape (square-well/Woods-Saxon) differences.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
Dirac equation, discontinuous potentials, Woods-Saxon potential, nuclear shell model, amplitude-phase method
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-249764 (URN)10.1088/1402-4896/ab08ac (DOI)000462893500001 ()
Note

QC 20190429

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-04-29Bibliographically approved
Thylwe, K.-E. (2018). Heavy-particle resonance phase shifts: an improved amplitude-phase formula. Journal of Mathematical Chemistry, 56(9), 2674-2690
Open this publication in new window or tab >>Heavy-particle resonance phase shifts: an improved amplitude-phase formula
2018 (English)In: Journal of Mathematical Chemistry, ISSN 0259-9791, E-ISSN 1572-8897, Vol. 56, no 9, p. 2674-2690Article in journal (Refereed) Published
Abstract [en]

An improved amplitude-phase formula suitable for non-relativistic heavy-particle resonance phase shifts is derived. The present formula makes use of two amplitude functions instead of one for a central potential; an inner amplitude which is non-oscillatory in the well region of the effective potential, and an outer amplitude function which is non-oscillatory far away from the origin of the effective potential. The low-energy limit is discussed in connection with Levinson's theorem. Numerical computations at resonance energies and graphical illustrations are presented. Numerical comparisons with an existing single-amplitude formula are made.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Elastic molecular scattering, Resonances, Phase shifts, Amplitude-phase method
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235100 (URN)10.1007/s10910-018-0910-9 (DOI)000443702300006 ()
Note

QC 20180917

Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2018-09-17Bibliographically approved
Thylwe, K.-E. & McCabe, P. (2018). Note on Resonant and Non-resonant Peaks in Electron-Atom Total Scattering Cross Sections. Communications in Theoretical Physics, 69(1), 28-30
Open this publication in new window or tab >>Note on Resonant and Non-resonant Peaks in Electron-Atom Total Scattering Cross Sections
2018 (English)In: Communications in Theoretical Physics, ISSN 0253-6102, E-ISSN 1572-9494, Vol. 69, no 1, p. 28-30Article in journal (Refereed) Published
Abstract [en]

Certain broad low-energy peaks caused by a single partial wave in total cross sections are explained in terms of phase shifts. Such peaks have been associated with the real part of a Regge pole trajectory, having a maximum near an integer value of the angular momentum quantum number. At the peak energies, the pertinent partial-wave phase shift was shown to have a local maximum near a value pi/2 modulo pi. This implies no time delay in the semiclassical context. The phenomenon is a quantum effect, lacking a semiclassical interpretation.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
scattering, resonances, quantum mechanics, cross sections
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-221947 (URN)10.1088/0253-6102/69/1/28 (DOI)000422832600006 ()2-s2.0-85040690052 (Scopus ID)
Note

QC 20180130

Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2018-02-02Bibliographically approved
Thylwe, K.-E. (2018). Semi-Relativistic Two-Body States of Spinless Particles with a Scalar-Type Interaction Potential. Communications in Theoretical Physics, 69(2), 127-130
Open this publication in new window or tab >>Semi-Relativistic Two-Body States of Spinless Particles with a Scalar-Type Interaction Potential
2018 (English)In: Communications in Theoretical Physics, ISSN 0253-6102, E-ISSN 1572-9494, Vol. 69, no 2, p. 127-130Article in journal (Refereed) Published
Abstract [en]

A semi-relativistic quantum approximation for mutual scalar interaction potentials is outlined and discussed. Equations are consistent with two-body Dirac equations for bound states of zero total angular momentum. Two-body effects near the non-relativistic limit for a linear scalar potential is studied in some detail.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
relativistic quantum mechanics, two-body effects, two-body scalar potentials, bound states, quark potential
National Category
Mathematical Analysis
Identifiers
urn:nbn:se:kth:diva-224039 (URN)10.1088/0253-6102/69/2/127 (DOI)000425414600002 ()2-s2.0-85042606910 (Scopus ID)
Note

QC 20180320

Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2018-03-20Bibliographically approved
Thylwe, K.-E. (2017). Two-Body Local-Momentum Approximation of Spinless Particles Scattered by a (1+1)-D Woods-Saxon Barrier Potential. Communications in Theoretical Physics, 67(6), 619-625
Open this publication in new window or tab >>Two-Body Local-Momentum Approximation of Spinless Particles Scattered by a (1+1)-D Woods-Saxon Barrier Potential
2017 (English)In: Communications in Theoretical Physics, ISSN 0253-6102, E-ISSN 1572-9494, Vol. 67, no 6, p. 619-625Article in journal (Refereed) Published
Abstract [en]

A local momentum (LM) approximation applicable to semi-relativistic two-body repulsive interactions is presented. It assumes negligible variations in the (vector-type) potential. A Woods-Saxon barrier with a rectangular-like shape is studied in some detail. The LM-approximation gives exact results within the semi-relativistic framework for rectangular barrier interactions in (1+1) dimensions. Further approximations of the local momentum approach leads to the two-body approximation of Ikhdair & Sever, known since the early 90's as the spinless Salpeter equation approximating the Bethe-Salpeter equation. LM- and GS-results indicate significant two-body effects. Results obtained from the (single-mass) Dirac equation are similar for certain two-body mass combinations.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2017
Keywords
barrier transmission, semi-relativistic, two-body effects
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-216473 (URN)10.1088/0253-6102/67/6/619 (DOI)000404108300004 ()2-s2.0-85021376866 (Scopus ID)
Note

QC 20171201

Available from: 2017-12-01 Created: 2017-12-01 Last updated: 2017-12-01Bibliographically approved
Thylwe, K.-E. (2015). Applications of the amplitude-phase method to symmetric double-well potentials. Journal of Mathematical Chemistry, 53(7), 1608-1616
Open this publication in new window or tab >>Applications of the amplitude-phase method to symmetric double-well potentials
2015 (English)In: Journal of Mathematical Chemistry, ISSN 0259-9791, E-ISSN 1572-8897, Vol. 53, no 7, p. 1608-1616Article in journal (Refereed) Published
Abstract [en]

An amplitude-phase method is used to derive general quantization conditions for energy levels in smooth double-well potentials. The resulting quantization condition is applied to symmetric double-well potentials, where the two types of symmetry levels are shown to be determined by separate quantization conditions.

Keywords
Mathematical methods, Semiclassical methods, Amplitude-phase method, Double-well potentials
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-172486 (URN)10.1007/s10910-015-0508-4 (DOI)000357289200007 ()2-s2.0-84983542728 (Scopus ID)
Note

QC 20150826

Available from: 2015-08-26 Created: 2015-08-25 Last updated: 2017-12-04Bibliographically approved
Thylwe, K.-E. & McCabe, P. (2015). On Calculations of Legendre Functions and Associated Legendre Functions of the First Kind of Complex Degree. Communications in Theoretical Physics, 64(1), 9-12
Open this publication in new window or tab >>On Calculations of Legendre Functions and Associated Legendre Functions of the First Kind of Complex Degree
2015 (English)In: Communications in Theoretical Physics, ISSN 0253-6102, E-ISSN 1572-9494, Vol. 64, no 1, p. 9-12Article in journal (Refereed) Published
Abstract [en]

Formulas for calculating Legendre functions and associated Legendre functions of the first kind of complex degree using an Ermakov-Lewis invariant are presented. These formulas are straight-forward to implement numerically and are motivated by the lack of computational routines in standard university tools like those of Mat Lab and Maple. Angular waves propagating in opposite directions are also obtained. The results are particularly useful in complex angular momentum theories and nearside/farside analysis of spin-dependent angular scattering from central potentials.

Keywords
ordinary differential equations, scattering theory
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-173783 (URN)000360216500002 ()2-s2.0-84937011074 (Scopus ID)
Note

QC 20150921

Available from: 2015-09-21 Created: 2015-09-18 Last updated: 2017-12-04Bibliographically approved
Hassanabadi, S., Ghominejad, M. & Thylwe, K. E. (2015). Two-body scattering in (1 + 1) dimensions by a semi-relativistic formalism and a Hulthén interaction potential. Communications in Theoretical Physics, 63(4), 423-426, Article ID 423.
Open this publication in new window or tab >>Two-body scattering in (1 + 1) dimensions by a semi-relativistic formalism and a Hulthén interaction potential
2015 (English)In: Communications in Theoretical Physics, ISSN 0253-6102, E-ISSN 1572-9494, Vol. 63, no 4, p. 423-426, article id 423Article in journal (Refereed) Published
Abstract [en]

Scattering solutions of two-body Spinless Salpeter Equation (SSE) are investigated in the center of mass frame with a repulsive, symmetric Hulthén potential in one spatial dimension. Transmission and reflection coefficients are calculated and discussed.

Keywords
Hulthén potential, Spinless Salpeter equation, Transmission and reflection coefficients
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-166987 (URN)10.1088/0253-6102/63/4/423 (DOI)000355192500004 ()2-s2.0-84927640740 (Scopus ID)
Note

QC 20150528

Available from: 2015-05-28 Created: 2015-05-21 Last updated: 2017-12-04Bibliographically approved
Thylwe, K.-E. & McCabe, P. (2014). A theoretical study of spin-angular behaviors of potential scattering resonances. Physica Scripta, 89(8), 085401
Open this publication in new window or tab >>A theoretical study of spin-angular behaviors of potential scattering resonances
2014 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, no 8, p. 085401-Article in journal (Refereed) Published
Abstract [en]

Resonance scattering of a Dirac particle (electron) in a screened Coulomb potential (of Lorentz vector type) is investigated. The so-called direct and spin-flip differential cross-sections (DCSs) for Dirac particles are analyzed by a partial-wave analysis, as well as the spin-polarization parameters, here denoted S, T and U. This model study of angular as well as energy behaviors shows that DCSs, at forward and backward angles, together with the polarization parameter. seem to be best indicators of energy and orbital angular momentum of sharp, isolated, resonances.

Keywords
resonance, electron spin, Dirac, differential cross-section, sharp resonance, polarization
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-155811 (URN)10.1088/0031-8949/89/8/085401 (DOI)000343295000025 ()2-s2.0-84905158396 (Scopus ID)
Note

QC 20141113

Available from: 2014-11-13 Created: 2014-11-13 Last updated: 2017-12-05Bibliographically approved
Thylwe, K.-E. & McCabe, P. (2014). Partial-wave analysis of particular peaks in total scattering cross sections caused by a single partial wave. European Physical Journal D: Atomic, Molecular and Optical Physics, 68(10), 323
Open this publication in new window or tab >>Partial-wave analysis of particular peaks in total scattering cross sections caused by a single partial wave
2014 (English)In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 68, no 10, p. 323-Article in journal (Refereed) Published
Abstract [en]

Certain broad low-energy peaks in the total cross sections relevant for electron-atom scattering are studied and found to be caused by a single partial wave. Such peaks are associated here with complex orbital angular momentum (Regge) pole trajectories. At the peak energies these S-matrix poles are in some neighborhood of an integer value and at the same time near its maximum real part value as a function of energy. Such peaks are found to have no time delays. Results are presented for the Dirac equation using three rational function Thomas-Fermi potential models, all with the same behavior at large and small radial distances.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-157619 (URN)10.1140/epjd/e2014-50409-7 (DOI)000344342100006 ()2-s2.0-84908405853 (Scopus ID)
Note

QC 20141211

Available from: 2014-12-11 Created: 2014-12-11 Last updated: 2017-12-05Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0149-341X

Search in DiVA

Show all publications