Astroparticle Physics

312 16 GlossaryFermi–Dirac distributionFermi energyFermi mechanismfermionFeynman diagramsfissionfixed-target experimentflareflatness problemflavourfluid equationThe energy distribution of fermions in its dependence on the temperature.Energy of the highest occupied electron level at absolute zero for afree Fermi gas (e.g., electron, neutron gas).Acceleration mechanism for charged particles by shock waves (the1.-order process) or extended magnetic clouds (the 2.-order process).A particle with half integer spin ( 1 2 , 3 2, etc.) if the spin is measuredin units of ¯h. An important consequence of this particular angularmomentum is that fermions are subject to the Pauli principle. ThePauli principle says that no two fermions can exist in the samequantum-mechanical state at the same time. Many properties ofordinary matter originate from this principle. Electrons, protons,and neutrons – all of them are fermions – just as the fundamentalconstituents of matter, i.e., quarks and leptons.Feynman diagrams are pictorial shorthands to describe the interactionprocesses in space and time. With the necessary theoreticaltools Feynman diagrams can be translated into cross sections. Inthis book the agreement is such that time is plotted on the horizontaland spatial coordinates on the vertical axis. Particles moveforward in space-time, while antiparticles move backwards.The splitting of heavier atomic nuclei into lighter ones. Fission isthe way how nuclear power plants produce energy.An experiment in which the beam of particles from an acceleratoris aimed at a stationary target.Short duration outburst from stars in various spectral ranges.In classical cosmology any value of Ω in the early universe evenslightly different from one would be amplified with time and drivenaway from unity. In contrast, in inflationary cosmology Ω is approachingexponentially a value of one, thus explaining naturallythe presently observed value of Ω = 1.02 ± 0.02. In classical cosmologysuch a value would have required an unbelievably carefulfine-tuning.Characterizes the assignment of a fermion (lepton or quark) to aparticle family or a particle generation.It describes the evolution of the energy density in its dependenceon the expansion rate, pressure, and density. It can be derived usingclassical thermodynamics.