Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL Particles in the hot, early Universe.

Particles This lecture: Particles in the hot early universe

The standard model of particle physics Leptons –electron q=-1 m=0.5 MeV –e-neutrino q=0 m<15 eV –muon q=-1 m=0.1 GeV – neutrino q=0 m<0.17 MeV –tau q=-1 m=1.8 GeV –tau-neutrino q=0 m<24 MeV

The standard model of particle physics Quarks –up q=2/3 m=6 MeV –down q=-1/3 m=10 MeV –strange q=-1/3 m=0.25 GeV –charm q=2/3 m=1.2 GeV –bottom q=-1/3 m=4.3 GeV –top q=2/3 m=180 GeV

The standard model of particle physics Vector bosons –photon q=0 m=0 –W boson q=+-1 m=80.3 GeV –Z boson q=0 m=91.2 GeV –gluon q=0 m=0

The standard model of particle physics Higgs boson –Higgs q=0 m < 1 TeV

Inflation is over The Universe is hot, and dominated by radiation. Radiation and matter in equilibrium: –pairs of hadrons or leptons radiation

Quarks Quarks are fundamental particles which may be the building blocks of all the hadrons. They have fractional charge 1/3 or 2/3 of the electronic charge 3 quarks make a proton, antiproton or neutron.

Free quarks Quarks are only created at very high energies. At K (10 9 eV) quark-antiquark pairs are created and annihilated just like electrons and positrons at 10 6 eV. When the temperature drops, quark- antiquark pairs annihilate, but the photons dont have enough energy to make quark-antiquark pairs anymore.

Then the quarks combine to make stable baryons –quarks are effectively forbidden in coloured combinations –colour is a quantum number of quarks, like spin in electrons. There are now virtually no free quarks –but the only way to destroy a quark is to annihilate it with an antiquark or combine it with other quarks - there could be a small number of free quarks hanging around with nowhere to go, relics of the primordial soup.