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F. Kleefeld

Publications and source records attributed to F. Kleefeld.

30 records · Page 2Linked to original sources
arXiv2003

On Symmetries in (Anti)Causal (Non)Abelian Quantum Theories

(Anti)causal boundary conditions being imposed on the (seemingly) Hermitian Quantum Theory (HQT) as described in standard textbooks lead to an (Anti)Causal Quantum Theory ((A)CQT) with an indefinite metric. Therefore, an (anti)causal neutral scalar field is not Hermitian, as one (anti)causal neutral scalar field consists of a non-Hermitian linear combination of two (Hermitian) acausal fields. Fundamental symmetries in (A)CQT are addressed. The quantum theoretical (transition) probability and antiparticle concepts are revised. Imaginary parts of cross sections and refraction indices are related.

hep-th↗
arXiv2003

SU(3) Mass Splittings for $\bar{q}q$ Mesons and $qqq$ Baryons

By comparing SU(3)-breaking scales of linear mass formulae, it is shown that the lowest vector, axial-vector, and scalar mesons all have a $\bar{q}q$ configuration, while the ground-state octet and decuplet baryons are $qqq$. Also, the quark-level linear $σ$ model is employed to predict similar $\bar{q}q$ and $qqq$ states. Finally, the approximate mass degeneracy of the scalar $a_0$(980) and $f_0$(980) mesons is demonstrated to be accidental.

hep-ph↗
arXiv2003

ISI and FSI in NN-->NNX reactions

The present status of the theoretical description of Initial (ISI) and Final State Interactions (FSI) in nucleon induced exclusive meson production processes close to threshold is reviewed. Shortcomings are addressed and new perspectives given.

nucl-th↗
arXiv2003

Consistent relativistic Quantum Theory for systems/particles described by non-Hermitian Hamiltonians and Lagrangians

A causal, non-Hermitian, renormalizable, local, unitary and Lorentz convariant formulation of Quantum Theory (QT) (= Quantum Mechanics (QM) and Quantum Field Theory (QFT)) is developed which is free of formalistic problems we face in the commonly used Hermitian formulation of QT. Side effects of the new formulation of QT are the derivation of a consistent (anti)causal neutrino Lagrangian, the enrichment of chiral symmetries, the removal of the Dirac sea, the separation of positive and negative energy states including a reformulation of the anti-particle concept and a critical analysis of the concept of probability currents. In a first step we apply the new formulation of QT to establish a relation between perturbative Quantum Chromodynamics (QCD) and the (axial)vector meson extended Quark-Level Linear Sigma Model (QLLSM) at high energies.

hep-ph↗
arXiv2002

Does it make any sense to talk about a Delta-isobar?

It is shortly investigated, on what basis an experimentally observed resonance like the Delta(1232)-isobar can be embedded into the framework of Quantum Theory (QT), i.e. Quantum Field Theory (QFT) and Quantum Mechanics (QM). After a short discussion of the particle concept in the context of the "bootstrap" idea of G. Chew and S. Mandelstam we will focus on the theoretical formalism being necessary to describe resonances in the Lagrangian or Hamiltonian formulation of QT.

nucl-th↗
arXiv2000

Model-independent definition and determination of electromagnetic formfactors and multipole moments

A theoretical method for the systematic definition and determination of Cartesian and spherical electromagnetic (onshell) formfactors and multipole moments for particles or composite systems from electromagnetic Breit-frame current distributions is presented. The method presented is free of sign ambiguities and is not based on the underlying analytical substructure of the electromagnetic current distributions. By construction the method contains all higher order momentum derivative terms within the definition of electromagnetic formfactors and multipole moments, which are not taken into account in a lot of existing theoretical calculations.

nucl-th↗
arXiv2000

ABSSM - a new field-theoretic method of describing scattering/production processes of composite particles by asymptotic in-/outgoing Bethe-Salpeter states

A new relativistic field-theoretic formalism called "Asymptotic Bethe-Salpeter State Method" (ABSSM) is presented, which allows to calculate both electromagnetic formfactors and hadronic scattering and production amplitudes of elementary and composite systems (being described by Bethe-Salpeter amplitudes) within one theoretical framework. The ABSSM is then applied to the deuteron as a composite system of two nucleons.

nucl-th↗
arXiv2000

ISI/FSI in Threshold Meson Production - Onshell Approach and Coulomb Problem

The onshell description of Initial- and Final-State-Interactions (ISI and FSI) of threshold meson production reactions is reviewed. Existing onshell models and their offshell extension are discussed. Unitarity constraints on enhancement factors are formulated. A strategy for the treatment of essential singularities connected to Coulomb-like FSI is given.

nucl-th↗
arXiv1998

Consistent effective description of nucleonic resonances in an unitary relativistic field-theoretic way

High energy strong interaction physics is successfully described by the local renormalizable gauge theory called Quantum-Chromo-Dynamics (QCD) with quarks and gluons as ``elementary'' degrees of freedom, while intermediate energy strong interaction physics shows up to be determined by a non-local, non--renormalizable effective field theory (EFT) of ``effective'' degrees of freedom like mesons, ground state baryons and resonances. Within the picture of an effective field theory of strong interaction at intermediate energies I present a ``toy-model'' in which fermionic and bosonic resonances are considered to be ``particles'', i.e. they consistently are described by (anti-)commuting effective field-operators (containing dynamics of infinitely many quark-gluon or meson-nucleon diagrams) which are comfortably treated by Wick's Theorem in a covariant framework and obey unitarity. Non-trivial implications to couplings of non-local interactions are shown.

nucl-th↗
arXiv1998

Protoninduced Pion-, Eta- and Kaon-Production at Threshold

We present some details of our recent theoretical investigations on the total cross section of the reactions $pp\to pp π^0$, $pp\to pp η$ and $pp\to pΛK^+$ at threshold. Applying standard nonrelativistic perturbation theory within the framework of meson exchange models (MEC) to all of the investigated processes we observe that theory is still far--off from a quantitative understanding of the existing data, although the qualitative behaviour of the threshold cross sections can be reproduced. The often quoted $η^2$--dependence of the $pp\to pp π^0$ cross section at threshold is due to a calculational mistake of Koltun and Reitan (1966) and not based on theoretical grounds, where threebody phasespace behaviour would yield $η^4$, which can be affected by final state and short range effects. To respect the high momentum transfers for $pp\to pp η$ and $pp\to pΛK^+$ relativistic models were developed. Hereby the $η$--production still is based on MEC, while the $K^+$ production was investigated in the quark-gluon-picture based on the Bethe--Salpeter formalism.

nucl-th↗