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A note on infraparticles and unparticlesSchroer, BertCentro Brasileiro de Pesquisas Físicas (CBPF)2008We remind the reader of the meaning and achievements of infraparticles which, although themselves not necessarily of zero mass, require the presence of zero mass in order get delocalized states with a singularity which dissolves the mass-shell in an inexorable way into the continuum and therefore renders the standard particle concept useless. These objects were recently rediscovered under the name unparticles The case of infraparticles also encompasses particle-like objects in conformal QFT when all multiparticle thresholds coalesce on top of each other and only the concept of a highly inclusive cross section survives of scattering theory. The infraparticle research has led to deep results and the recently discovered semiinfinite string-localized vectorpotentials have led to new interesting ideas of dealing with physical electrically charged states and a generalized scattering theory. We explain why unparticles are identical to the old infraparticles. Using this relation it is shown that unparticles/infraparticles cannot lead to a natural description of darkness of dark matter. A more radical scenario for darkness comes from semiinfinite string-localized vectorpotentials in a reformulated version of nonabelian gauge theory.
Particle physics in the 60 and 70 and the legacy of contributions by J. A. SwiecaSchroer, Bert-2007After revisiting some high points of particle physics and QFT of the two decades from 1960 to 1980, I comment on the work by Jorge Andr'e Swieca. I explain how it fits into the development of QFT during these two decades and draw attention to its legacy in the ongoing particle physics research.