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Understanding BBN, Neutrinos, and the CBR: Probing the Early Universe

This work explores the interplay between Big Bang Nucleosynthesis (BBN), neutrinos, and Cosmic Microwave Background Radiation (CBR) as critical components in understanding the early universe's evolution. It discusses the roles of neutrinos during key epochs, including the implications of baryon density and expansion rates derived from both BBN and CBR observations. Key results show that predictions of primordial abundances and parameters such as deuterium and helium mass fractions align with data, providing insights into the universe's expansion and the behavior of fundamental particles shortly after the Big Bang.

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Understanding BBN, Neutrinos, and the CBR: Probing the Early Universe

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  1. BBN, NEUTRINOS, AND THE CBR Gary Steigman (with J. P. Kneller & V. Simha) Center for Cosmology and Astro-Particle Physics Ohio State University PPC 2007, TAMU, May 14 – 18, 2007

  2. ~ 100 s after the Big Bang Primordial Nucleosynthesis ~ 0.1 s after the Big Bang Neutrinos Decouple ~ 380 kyr after the Big Bang Relic Photons (CBR) are free

  3. BBN(~20Minutes)& The CBR(~400kyr) Provide Complementary Probes Of The Early Evolution Of The Universe * Neutrinos Play Important Roles At Both Epochs Do predictions and observations of the baryon density (10(nB/nγ)0=274 Bh2) and expansion rate (H) of the Universe agree at these different epochs?

  4. The Early, Hot, Dense Universe Is A Cosmic Nuclear Reactor As the Universe expands and cools, BBN “begins” at T 70 keV (when n / p 1 / 7) Coulomb barriers and the absence of free neutrons end BBN at T 30 keV tBBN 424 min.

  5. BBN – Predicted Primordial Abundances 4He Mass Fraction BBN Abundances ofD, 3He, 7Li are RATE (Density) LIMITED 7Li 7Be D, 3He, 7Li are potential BARYOMETERS

  6. DEUTERIUM --- TheBaryometerOf Choice • As the Universe evolves,D is only DESTROYED  • * Anywhere, Anytime : (D/H) t  (D/H) P • * For Z << Z : (D/H) t (D/H) P (Deuterium Plateau) • (D/H) P is sensitive to the baryon density (    ) • H  and D areseen in Absorption,BUT … • * H and D spectra are identical  H Interlopers? • * Unresolved velocity structure  Errors in N(H) ?

  7. D/H vs. Metallicity Low – Z / High – z QSOALS Deuterium Plateau ? Real variations, systematic differences, statistical uncertainties ?

  8. D/H vs. Metallicity For Primordial D/H adopt the mean For the error adopt the dispersion around the mean 105(D/H)P= 2.68± 0.27

  9. D + SBBN10 =6.0± 0.4 SBBN

  10. CBR

  11. CBR Temperature Anisotropy Spectrum (T2 vs. ) Depends On The Baryon Density  10=4.5,6.1,7.5 CBR constrains 10 V. Simha & G.S. The CBR is an early - Universe Baryometer

  12. CBR10 =6.1±0.2 CBR V. Simha & G.S. (2007)

  13. CBR & SBBN (D) Agree ! SBBN

  14. The Expansion Rate (H  Hubble Parameter) provides a probe of Non-Standard Physics • S  H/ H  (/)1/2  (1 + 7N /43)1/2    + N  and N  3 + N • 4He is sensitive to S while D probes  4He provides a Chronometer D provides a Baryometer

  15. Do SBBN Predictions of D and 4He Agree ? As O/H  0, Y  0 SBBN Prediction

  16. Likelihoods (SBBN) from D and 4He AGREE ?

  17. D & 4He Isoabundance Contours YP & yD  105 (D/H) 4.0 2.0 3.0 0.25 0.24 0.23 Kneller & Steigman (2004)

  18. BBN (D, 4He)  For N ≈ 2.4 ± 0.4 YP & yD  105 (D/H) 4.0 3.0 2.0 0.25 0.24 0.23 D&4HeIsoabundance Contours Kneller & Steigman (2004)

  19. NSBBN (D & 4He)  10 = 5.7 ±0.4 NSBBN

  20. BBN (20 min) & CBR (380 kyr) AGREE on 10

  21. NSBBN (D & 4He)N =2.4 ± 0.4 NSBBN

  22. CBR Temperature Anisotropy Spectrum Depends on the Radiation Density R(SorN)   N =1, 3,5 CBR constrainsN(S) V. Simha & G.S. The CBR is an early - Universe Chronometer

  23. N =2.3 (1.2 ≤ N≤ 4.4 @ 68%) CBR

  24. BBN (20 min) & CBR (380 kyr) AGREE on N CBR BBN

  25. BBN (D & 4He) BBN Constrains N N < 4 N> 1 V. Simha & G.S.

  26. CBR CBR Constrains10 V. Simha & G.S.

  27. BBN (D & 4He) & CBR AGREE ! V. Simha & G.S.

  28. BBN and Primordial (Pop ) Lithium Li too low ? [Li]12 + log(Li/H) 2.6 – 2.7 Lithium ( “Spite” ) Plateau (?) [Li]  12 + log(Li/H) 2.1

  29. Even for N  3 yLi  1010 (Li/H) • Y + DH • Li H  4.0  0.7 x 1010 • log (Li) 2.6 0.1 (vs. log (Li)obs  2.2) 4.0 3.0 2.0 4.0 0.25 0.24 0.23 Li depleted/diluted in Pop  stars ?

  30. Summary : Baryon Density Determinations D & 3He agree with the CBR Depleted ? N< 3 ?

  31. Summary : N Determinations 95% Ranges

  32. SUCCESS BBN (D & 4He) and the CBR Agree ! (Lithium ?) CHALLENGE (The Theorist’s Mantra) More & Better Data Are Needed !

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