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Unformatted text preview: COSMOLOGY Problem Set 9 May 24, 2010 Problem 1 : Variations on SBBN a) Some recent experiments suggest that the neutron lifetime may be smaller than the currently accepted value. Suppose this were true and describe, qualitatively, the effect this would have on the primordial abundances of the nuclides produced during BBN.  b) Suppose, as suggested by some extensions of the standard model of particle physics, that there is a massive, unstable particle X . Suppose the X is non-relativistic at BBN and decays only long after BBN has ended. If at BBN, ρ X ≫ ρ ER , describe the effect on the primordial abundances of the nuclides produced during BBN. In particular, compared to SBBN, explain if the abundances of D, 4 He, 7 Li be higher or lower.  c) Suppose at BBN Newton’s gravitational constant were smaller that its value today by 10% ( G BBN /G = 0 . 9). At T γ = 1 MeV find: g eff , Δ N ν , and the speed-up factor S . If all other physics were unchanged, would more or less 4 He be produced during...
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