Holger Bech Nielsen
Holger Bech Nielsen ( born August 25, 1941 in Copenhagen ) is a Danish theoretical physicist and had from 1990 to 2012 held the Chair of High Energy Physics at the Niels Bohr Institute, University of Copenhagen. Nielsen is known for his public talks and for his original, sometimes speculative ideas on particle physics.
Life and work
Nielsen studied from 1961 in Copenhagen physics and received his doctorate in 1968 at the Niels Bohr Institute on " Some consequences of the self-consistency of the quark model." 1969 and 1971 he was a Fellow of the NORDITA in Copenhagen and 1971/72 visiting scientists at CERN ( again 1999/2000). 1973 to 1985 he was a lecturer at the Niels Bohr Institute, then he became a research professor, from 1990 professor of high energy physics.
Several theoretical concepts are named after him. With Poul Olesen 1973, he led the Nielsen - Olesen - vertex and Nielsen Olesen vortex in the early string theory one. and with Koba Koba -Nielsen 1974 variable and KNO scaling ( Koba -Nielsen - Olesen scaling ) The Nielsen - Ninomiya theorem explains why it is so difficult (chiral ) represent fermions on the lattice. Either one fermion doublings or broken chiral symmetry (ie no fermions with a small mass near zero, as neutrinos ). Froggatt and Nielsen discuss spontaneously broken family symmetry to explain the mass hierarchy in the three fermion families ( Froggatt -Nielsen mechanism). The FNns Mechanism ( Foerster -Nielsen - Ninomiya - Shenker mechanism) describes the emergence of exact gauge symmetry on large scales only approximate symmetry at the local level. Nielsen tracked for a long time a program that fundamental laws of nature from a random dynamics (random dynamics) to explain at the local level.
Ken Jonson called a concept of Nielsen among others. in the Chiral Bag Model the " Cheshire Cat Principle" ( CCP), after the disappearance of smiles with the Cheshire Cat in Lewis Carroll's own "Alice in Wonderland". A fundamental theory with fermions "disappears" in the low-energy QCD in an effective meson theory. One theory is used for the description of the nucleon in the bag used ( quarks, gluons ), the other outside. At the edge of the bag parameters of the two theories to be adjusted. The CCP says this is the physics of the model from the exact value of the radius independent.
He is a member of the Danish Academy of Sciences and the Norwegian Academy of Sciences. In 2001 he received the German Humboldt Award.