Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session E2: Primordial Nucleosynthesis |
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Sponsoring Units: DNP Chair: Carl R. Brune, Ohio University Room: Hyatt Regency Dallas Landmark B |
Saturday, April 22, 2006 3:30PM - 4:06PM |
E2.00001: Light Elements on Fire: Nuclear Information for Big Bang Studies Invited Speaker: Within the last decade, our notions of the cosmos have been radically altered by precision observations of the light from distant Type Ia supernovae and, separately, the power spectrum of the cosmic microwave afterglow of the Big Bang. These show that the expansion of the universe is actually accelerating, and that the Universe is overwhelmingly composed of a mysterious dark energy (75\%) and dark matter (21\%), with only 4\% of the total being baryonic ``normal'') matter. Determining the amount and characteristics of dark matter, dark energy, and normal matter is one of the most compelling problems in astrophysics today. A complementary and independent approach to determine the baryonic matter density is to compare the predictions of the abundances of ``primordial'' light elements (H, He, Li) formed three minutes after the Big Bang with observations of these elements in the interstellar medium and on the surface of very old stars. ``Big Bang Nucleosynthesis'' (BBN) calculations require, as input, thermonuclear reaction rates at the high temperatures characteristic of the early universe. BBN estimates of the $^2$H, $^4$He, and $^7$Li abundances imply a baryonic density that, respectively, agrees, marginally agrees, and disagrees with the density from other approaches. This discordance, and the current status of nuclear physics information for BBN studies, will be reviewed, and reactions needing additional measurements will be discussed. [Preview Abstract] |
Saturday, April 22, 2006 4:06PM - 4:42PM |
E2.00002: Observations of the Light Element Abundances and the Cosmological Baryon Density Invited Speaker: Three methods of measuring the mean cosmological density of baryons now agree within about 10 to 30{\%}: the cosmic microwave background, the D/H ratio using Standard Big Bang Nucleosynthesis, and the Lyman-alpha absorption from neutral Hydrogen in the intergalactic medium. Using this baryon density, Standard Big Bang Nucleosynthesis predicts a factor 3 to 4 more 7Li than is seen in halo stars. There are theoretical models that can allow halo stars to destroy 7Li, but these models are challenged by both the amount of destruction and the lack of variation amongst stars with different mass. We do not know whether these stars did destroy their 7Li. The baryon density also predicts systematically more 4He that most measurements over the last 20 years. We review the measurements and modifications to BBN that might explain the tension between D, He and Li. [Preview Abstract] |
Saturday, April 22, 2006 4:42PM - 5:18PM |
E2.00003: CMB-BBN complementarity Invited Speaker: I will review the measurement of eta, the photon-to-baryon ratio, coming from observations of the cosmic microwave background. Eta is also obtained independently from the measurements of light element abundances. These two independent determinations of eta amount to a consistency check on (and hence a test of) the standard model of cosmology. If our standard model of cosmology passes this test we obtain constraints on non-standard features, such as decaying particles, or new particle interactions. If we are willing to assume the standard model, the measurement of eta from the cosmic microwave background can be taken as a starting point for standard BBN, which would give definite predictions for the primordial abundances of light elements, a key input for other areas of cosmology. I will discuss how this results in an additional consistency check due to the sensitivity of the CMB anisotropies to the Helium abundance. [Preview Abstract] |
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