Astroparticle Physics

300 16 GlossaryMeasurement of extensive air showers via their produced Cheren-kov light in the atmosphere.AGNair-shower Cherenkov techniquealpha decayAMANDAAndromeda NebulaÅngströmannihilationanthropic principleantigravitationantimatterantiparticlesActive Galactic Nucleus. If one assumes that black holes poweredby infalling matter reside at centers of AGNs and if these AGNsemit polar jets, then the different AGN types (Seyfert galaxies, BL-Lacertae objects, radioquasars, radiogalaxies, quasars) can be understoodas a consequence of the random direction of view fromEarth.Nuclear decay consisting of the emission of an α particle (helium-4nucleus).Antarctic Muon And Neutrino Detector Array for the measurementof high-energy cosmic neutrinos.M31, one of the main galaxies of the local group; distance from theMilky Way: 700 kpc.The unit of length equal to 10 −10 m.A process, in which particles and antiparticles desintegrate, e.g.,e + e − → γγ.One might ask why the universe is as it is. If some of the physicsconstants which describe our universe were not finely tuned, thenit would have grossly different properties. It is considered highlylikely that life forms as we know them would not develop underan even slightly different set of basic parameters. Therefore, if theuniverse were different, nobody would be around to ask why theuniverseisasitis.Repulsive gravitation caused by a negative pressure as a conse-quence of a finite non-zero cosmological constant.Matter consisting only of antiparticles, like positrons, antiprotons,or antineutrinos. When antimatter particles and ordinary matterparticles meet, they annihilate mostly into γ rays (e.g., e + e − →γγ).For each particle there exists a different particle type of exactlythe same mass but opposite values for all other quantum numbers.This state is called antiparticle. For example, the antiparticle of anelectron is a particle with positive electric unit charge, which iscalled positron. Also bosons have antiparticles apart from those forwhich all charge quantum numbers vanish. An example for this isthe photon or a composite boson consisting of a quark and its correspondingantiquark. In this particular case there is no distinctionbetween particle and antiparticle, they are one and the same object.