Astroparticle Physics

322 16 GlossaryMpcMSW effectMtheorymultiplicitymultiversemuonmuon numberNInteraction mechanism mediated by the exchange of a virtual neu-tral gauge boson.negative pressureneutral currentneutralinoneutrinoMegaparsec (see parsec).Matter oscillations first proposed by Mikheyev, Smirnov, andWolfenstein; see matter oscillation.Supersymmetric string theory (‘superstring theory’) unifying allinteractions. In particular, the M theory also contains a quantumtheory of gravitation. The smallest objects of the M theory are p-dimensional membranes. It appears now that all string theories canbe embedded into an 11-dimensional theory, called M theory. Outof the 10 spatial dimensions 7 are compactified into a Calabi–Yauspace.Number of secondary particles produced in an interaction.Hypothetical enlargement of the universe in which our universe isonly one of an enormous number of separate and distinct universes.µ; the muon belongs to the second family of charged leptons. It hasthe electric charge −1.The muon µ − and its associated muon neutrino have the muoniclepton number +1, their antiparticles the muonic lepton number−1. All other elementary particles have the muon number 0. Themuon number – except for neutrino oscillations – is a conservedquantity.In the same way as a positive pressure increases gravitation throughits field, negative pressure (like, for example, in a spring) leads toa repulsive gravity. Dark energy represents a form of energy that isgravitationally repulsive, due to its negative effective pressure.Candidate for a non-baryonic dark-matter particle. In the frame-work of supersymmetry fermions and bosons come in supermultiplets.The neutralino is the bosonic partner of the neutrino. Thelightest supersymmetric partner is expected to be stable and wouldtherefore be a good dark-matter candidate.A lepton without electric charge. Neutrinos only participate inweak and gravitational interactions and therefore are very difficultto detect. There are three known types of neutrinos, which are allvery light. These leptons are ν e , ν µ ,andν τ for the electron, muon,and tau family. At the LEP experiments it could be shown that apartfrom the three already known neutrino generations there is no furthergeneration with light neutrinos (m ν < 45 GeV/c 2 ).