Astroparticle Physics

16 Glossary 319Short for Large Electron–Positron Collider, the e + e − storage ringat CERN with a circumference of 27 km.The production of leptons in the early universe.A fundamental fermion which does not participate in strong interactions.The electrically charged leptons are the electron (e), themuon (µ),andthetau(τ), and their antiparticles. Electrically neutralleptons are the associated neutrinos (ν e , ν µ , ν τ ).Quantum number describing the lepton flavour. The three generationsof charged leptons (e − , µ − , τ − ) have different individuallyconserved lepton numbers, while their neutrinos are allowed to oscillate,thereby violating lepton-number conservation.Large Hadron Collider at CERN in Geneva. In the LHC protonswill collide with a center-of-mass energy of approximately 14 TeV.LHC is expected to start operation in 2007. LHC will be the acceleratorwith the highest center-of-mass energy in the world. It isgenerally hoped that the physics of the Large Hadron Collider willhelp to clarify some open questions of particle physics, for example,the question whether the Higgs boson responsible for the generationof masses of fundamental fermions exists and which massit has.The distance traveled by light in vacuum during one year; 1 ly =9.46 × 10 15 m = 0.307 pc.The model that explains pulsars as flashes of light from a rotatingpulsar.Irregular galaxy in the southern sky at a distance of 170 000 lightyears(̂= 52 kpc).A system of galaxies comprising among others our Milky Way, theAndromeda Nebula, and the Magellanic Clouds. The diameter ofthe local group amounts to approximately 5 million light-years.Virgo supercluster; ‘Milky Way’ of galaxies to which also the localgroup and the Virgo cluster belong. Its extension is approximately30 Mpc.Feature emerging from special relativity in which a moving objectappears shortened along its direction of motion.Transformation of kinematical variables for frames of referencewhich move at linear uniform velocity with respect to each otherunder the consideration that the speed of light in vacuum is amaximum velocity.LEPleptogenesisleptonlepton numberLHClight-yearlighthouse modelLMC – Large Magellanic Cloudlocal grouplocal superclusterLorentz contractionLorentz transformation