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