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Search Results: 1 - 10 of 10655 matches for " Andreas Aste "
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A Direct Road to Majorana Fields
Andreas Aste
Symmetry , 2010, DOI: 10.3390/sym2041776
Abstract: A concise discussion of spin-1/2 field equations with a special focus on Majorana spinors is presented. The Majorana formalism which describes massive neutral fermions by the help of two-component or four-component spinors is of fundamental importance for the understanding of mathematical aspects of supersymmetric and other extensions of the Standard Model of particle physics, which may play an increasingly important role at the beginning of the LHC era. The interplay between the two-component and the four-component formalism is highlighted in an introductory way. Majorana particles are predicted both by grand unified theories, in which these particles are neutrinos, and by supersymmetric theories, in which they are photinos, gluinos and other states.
The position of the quasielastic peak and electron Coulomb distortion in (e,e') scattering
Andreas Aste
Physics , 2006,
Abstract: The position of the quasielastic peak for (e,e') scattering off 208-Pb extracted from a selected data set measured at Saclay is related to a heuristic theoretical description. An analysis of the data shows that the peak position can be described very accurately by a simple equation in the relevant kinematic region where a pronounced peak is observable. The simple findings result in a concluding comment related to recent calculations concerning the Coulomb distortion in (e,e') scattering for heavy nuclei.
Bound-free pair production cross section in heavy-ion colliders from the equivalent photon approach
Andreas Aste
Physics , 2007, DOI: 10.1209/0295-5075/81/61001
Abstract: Exact calculations of the electron-positron pair production by a single photon in the Coulomb field of a nucleus with simultaneous capture of the electron into the K-shell are discussed for different nuclear charges. Using the equivalent photon method of Weizsaecker and Williams, a simple expression for the bound-free production of electron-positron pairs by colliding very-high-energy fully stripped heavy ions is derived for nuclei of arbitrary charge.
Coulomb distortion effects in quasi-elastic (e,e') scattering on heavy nuclei
Andreas Aste
Physics , 2007, DOI: 10.1016/j.nuclphysa.2008.03.011
Abstract: The influence of the Coulomb distortion for quasi-elastic (e,e') scattering on highly charged nuclei is investigated in distorted wave Born approximation for electrons. The Dirac equation is solved numerically in order to obtain exact electron continuum states in the electrostatic field generated by the charge distribution of an atomic nucleus. Different approximate models are used to describe the nucleon current in order to show that, at high electron energies and energy-momentum transfer, the influence of Coulomb distortions on (e,e') cross sections can be reliably described by the effective momentum approximation, irrespective of details concerning the description of the nuclear current.
Comment on `A simple explanation of the non-appearance of physical gluons and quarks'
Andreas Aste
Physics , 2003, DOI: 10.1139/p03-056
Abstract: In a recent paper by Johan Hansson [hep-ph/0208137] it is claimed that the non-appearance of quarks and gluons as physical particles is an automatic result of the nonabelian nature of the color interaction in quantum chromodynamics. It is shown that the arguments given by Hansson are insufficient to support his claim by giving simple counter arguments.
Symmetrien, Teilchen und Felder
Andreas Aste
Physics , 2014,
Abstract: Symmetries are playing a very prominent role in natural sciences. In mathematics as the language of physics, symmetries are treated within the framework of group theory, which provides the tools to classify natural laws and physical objects like elementary particles. The present work discusses aspects of relativistic quantum field theory as the mathematical theory of particle physics which are relevant for the modern description of elementary particles and their associated fields hitherto considered as fundamental building blocks of the theory. Due to the abstract nature of quantum field theory, these aspects can only be touched by their exemplification within a review.
Coulomb solutions from improper pseudo-unitary free gauge field operator translations
Andreas Aste
Physics , 2014, DOI: 10.3390/sym6041037
Abstract: Fundamental problems of quantum field theory related to the representation problem of canonical commutation relations are discussed within a gauge field version of a van Hove-type model. The Coulomb field generated by a static charge distribution is described as a formal superposition of time-like pseudo-photons in Fock space with a Krein structure. In this context, a generalization of operator gauge transformations is introduced to generate coherent states of abelian gauge fields interacting with a charged background.
Die kontrollierte Kettenreaktion
Andreas Aste
Physics , 2012,
Abstract: A concise discussion of the basic principles of the controlled nuclear chain reaction is presented.
Complex representation theory of the electromagnetic field
Andreas Aste
Physics , 2012, DOI: 10.7546/jgsp-28-2012-47-58
Abstract: A concise discussion of the 3-dimensional irreducible (1,0) and (0,1) representations of the restricted Lorentz group and their application to the description of the electromagnetic field is given. It is shown that a mass term is in conflict with relativistic invariance of a formalism using electric and magnetic fields only, contrasting the case of the two-component Majorana field equations. An important difference between the Dirac equation and the Dirac form of Maxwell's equations is highlighted by considering the coupling of the electromagnetic field to the electric current.
Fock Vacuum Instability and Causality
Andreas Aste
Physics , 2001,
Abstract: The vacuum diagram is calculated at second order for theories with self-interacting massless fields in the framework of finite causal perturbation theory. It is pointed out that the infrared behaviour of the vacuum diagram leads to unstable Fock vacua for QCD or massless QED, but not for quantum gravity. Therefore a radical rearrangement of the physical system must take place for such theories. Conversely, stability of the Fock vacuum for massless interacting fields is another hint at the possibility that quantum gravity should be treated as an effective theory.
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