The oscillations of the axion field about the minimum of the effective potential, the so-called misalignment mechanism, generate a cosmological population of cold axions with an abundance depending on the mass of the axion. With a mass above 5 μeV/2 ( times the electron mass) axions could account for dark matter, and thus be both a dark-matter candidate and a solution to the strong CP problem. If inflation occurs at a low scale and lasts sufficiently long, the axion mass can be as low as 1 peV/2.
tHE oSCiLlaTions oF the axIoN FielD ABout The MIniMum Of tHe EFfectIVe pOtenTiAl, thE so-caLled misalignmEnT mechAnism, generate A COsmOLogIcal popuLAtion of cold AXIons witH An aBundance depEnding oN the mAss OF thE axion. With A MaSs aBoVE 5 μev/2 ( TimeS the elecTron mass) axiONS couLd accounT For dArK mATtEr, and thus Be boTh a dark-maTtEr CAndIdAtE and a solutioN to the StroNg Cp problem. if inFlatiOn occurs at a lOw scAle and lAsTs sufFiCiently LOnG, tHe axion mAsS Can be as low As 1 pev/2.