BBN: Constraints from CMB experiments Joanna Dunkley University of Oxford IAUS Geneva, Nov

Universe starts out hot, dense and filled with radiation. As the universe expands, it cools. During the first minutes, light elements form After 400,000 years, atoms form After ~100,000,000 years, stars start to form After ~1 Billion years, galaxies and quasars

CMB as probe of fluctuations Linear theory Basic elements have been understood for 30 years (Peebles, Sunyaev & Zeldovich) Numerical codes agree to better than 0.1% (Seljak et al 2003)

Constraining baryon density Competition between gravity and pressure in acoustic oscillations. Odd peaks are compressions, even are rarefactions. More baryons: enhance the compressions. At small scales, less Silk damping. We measure one number: Ω b h 2

WMAP 5-yr data Hinshaw et al 2009

Hinshaw et al 2008 Actual multi- frequency maps (23-94 GHz)

Text Cosmic variance limited to l=530 Hinshaw et al 2009 WMAP power spectrum

ΛCDM Cosmological Model Flat universe filled with baryons, CDM, cosmological constant, neutrinos, photons. Gaussian, adiabatic, nearly scale-invariant fluctuations Baryon density is ± Dunkley et al 2009

Relating to familiar quantities Baryon-to-photon ratio η 10 (WMAP) = 6.23 ± 0.17 For given ratio, can predict the element abundances (or for given abundance measurements can infer the ratio) Element Inferred ratio η 10 Deuterium6.0 ± Helium Helium Lithium3 ± 0.6 Steigman 2007 Not most up to date: see Gary Steigman’s talk

Primordial helium fraction Number density of electrons before recombination n e = n b (1 − Y ) We usually assume Y = 0.24 for CMB analysis. But smaller ne (larger Y) increases mean free path of Compton scattering, giving more Silk damping on small scales Current CMB limits: Y< 0.45 (95% CL, WMAP5, Dunkley et al 2009) In the end, Y and baryon density should be consistent in SBBN. Too early to tell from CMB. Trotta & Hansen 2004

Prospects for Planck (Planck Blue Book) (Mortonson & Hu 2008) From Planck: Sigma(Ω b h 2 ) = (three times better) Sigma(Y) = for Planck (>10 times better)

Measuring relativistic species Relativistic species, e.g. neutrinos, that don’t couple to photons/baryons, affect expansion rate and acoustic oscillations. From CMB Neff = Change the abundance prediction.

Prospects for Planck and ACT/SPT (Dunkley et al 2009) Want to make sure the CMB-inferred Neff is consistent with BBN- inferred measure. Errors on Neff=0.24 from Planck. ACT/SPT limits of about 0.4. Both small scale temperature and polarization help. Discrepancy could be sign of non-standard behavior

Summary The CMB power spectrum provides a constraint on baryon density at time of recombination. Data from WMAP tells us Ω b h 2 = ± , or η 10 =6.23 ±0.17. This is consistent with Deuterium (and 3He) measures, but tension with lithium and somewhat 4He. We can also try to measure helium fraction directly from CMB to check SBBN, but currently weak constraints (Y<0.45). Planck (and ACT/SPT) will improve both these numbers with small-scale measurements. Also measure Neff, number of relativistic species with CMB. Errors are now 1.5, consistent with BBN. Errors should soon be 0.2 from Planck. Can compare to the inferred number from BBN to check consistency.