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 1013 K (109 eV) quark-antiquark pairs are created and annihilated just like electrons and positrons at 106 eV.

• When the temperature drops, quark-antiquark pairs annihilate, but the photons don’t 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.