bbn10 - The Universe is expanding The Universe is filled...

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Unformatted text preview: The Universe is expanding The Universe is filled with radiation The Early Universe was Hot & Dense The Early Universe was a Cosmic Nuclear Reactor! Neutron Abundance vs. Time / Temperature p + e- n + e (n/p) eq BBN Begins Decay Freeze Out ? Wrong! Rates set by n Statistical Errors versus Systematic Errors ! History of n measurements 885.7 0.8 sec BBN Begins at T 70 keV when n / p 1 / 7 Coulomb Barriers and absence of free neutrons terminate BBN at T 30 keV t BBN 4 24 min. Pre - BBN Post - BBN Only n & p Mainly H & 4 He Baryon Density Parameter : B Note : Baryons Nucleons B n N / n ; 10 1 0 10 B = 274 B h 2 Hubble Parameter : H = H(z) In The Early Universe : H 2 G Standard Big Bang Nucleosynthesis (SBBN ) An Expanding Universe Described By General Relativity, Filled With Radiation, Including 3 Flavors Of Light Neutrinos (N = 3) The relic abundances of D, 3 He, 4 He, 7 Li are predicted as a function of only one parameter : * The baryon to photon ratio : B 10 More nucleons less D Evolution of mass - 2 More nucleons less mass - 3 Two pathways to mass - 3 Two pathways to mass - 7 BBN abundances of masses 6, 9 11 Abundances Are Very Small ! n / p 1 / 7 Y 2n / (n + p) 0.25 All / most neutrons are incorporated in 4 He Y is very weakly dependent on the nucleon abundance Y 4 He Mass Fraction Y 4y/(1 + 4y) y n(He)/n(H) Y P DOES depend on the competition between wk & H BBN Abundances of D , 3 He , Li D, 3 He, 7 Li are potential BARYOMETERS SBBN Predicted Primordial Abundances 7 Li 7 Be 4 He Mass Fraction Mostly H & 4 He Measure ( D / H ) P Use BBN ( D / H ) P vs. 10 to constrain B Infer B ( B ) at ~ 20 Min. Predict (D/H) P 4 He (mass fraction Y) is NOT Rate Limited Expansion Rate Parameter : S H/ H S H/ H ( / ) 1/2 (1 + 7 N / 43) 1/2 where + N and N 3 + N 4 He IS n/p Limited Y is sensitive to the EXPANSION RATE ( H 1/2 ) S 2 (H / H) 2 = G /...
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This note was uploaded on 07/28/2011 for the course PHY 880.20 taught by Professor Steigman during the Spring '10 term at Ohio State.

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bbn10 - The Universe is expanding The Universe is filled...

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