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Study Report

Study Report. Particle Astrophysics D.H. PERKINS Chapter 2.10. Che -Yu Chen 2010-3-06. Primordial nucleosynthesis. Weak reactions in equilibrium Neutron decay The formation reaction begins. Weak reactions in equilibrium.

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Study Report

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  1. Study Report Particle Astrophysics D.H. PERKINS Chapter 2.10 Che-Yu Chen 2010-3-06

  2. Primordial nucleosynthesis • Weak reactions in equilibrium • Neutron decay • The formation reaction begins

  3. Weak reactions in equilibrium • After baryogenesis, the neutrons and protons are in equilibrium by the weak reactions. • The ratio of neutrons and protons is determined by the Boltzmann factors.

  4. Neutron decay • After the rate of these weak reactions becomes smaller than the universe expand rate, the reactions are ‘’freeze-out’’. • Accompanied with neutrino decoupling. • kT=0.80MeV • Mn(0)/Mp(0)=0.20

  5. Neutron decay • Neutrons disappear by decay

  6. The formation reaction begins • At kT=0.05MeV, nucleosynthesis can begin with the formation of deuterons: • It’s at t ~ 300s(derived from )

  7. Other reactions There are no stable nuclei with A=5, 6 or 8 . The further formation has to await to the onset of helium burning in stars core.

  8. The helium mass fraction

  9. The primordial abundances

  10. Evolution of the universe in the Big Bang model

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