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Cosmology from CMB

Cosmology from CMB. Dmitry Pogosyan University of Alberta. Lecture 1: What can Cosmic Microwave Background tell us about the Universe ? A theoretical introduction. Lecture 2: Recent successes in the mapping of CMB anisotropy: what pre-WMAP and WMAP data reveals.

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Cosmology from CMB

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  1. Cosmology from CMB Dmitry Pogosyan University of Alberta • Lecture 1: What can Cosmic Microwave Background tell us about the Universe ? A theoretical introduction. • Lecture 2: Recent successes in the mapping of CMB anisotropy: what pre-WMAP and WMAP data reveals. Lake Louise, February, 2003

  2. Fundamentals of cosmology: Expansion of the Universe H0 = 72  8 km/s/Mpc (HST key project, 2001)

  3. P ≈ -ρρ = const P = 0 ρ = 1/a3 P ≈ 0 ρ = 1/a3 P = ρ/3 ρ = 1/a4 Dark energy ~ 70% Dark matter ~ 30% Baryons ~ 5% 3K Radiation ~0.01% Matter constituents according to modern view

  4. Fundamentals of cosmology: existence of Large-Scale Structures ¿Dark? Matter 8 ~ 1, averaged in spheres of 8 Mpc radius

  5. What do cosmologists want to learn about the Universe ? • Matter content • Geometry of the space • Origin of structures and details of their formation • Origin of the Universe as we observe now. What theory describes the early epoch of evolution ?

  6. Cosmic Microwave Background • Discovered 1965 (Penzias & Wilson) • 2.7 K mm-cm wavelentgh • 400 photons/cm3 • Isotropic • 1992 COBE satellite measures anisotropies ~ 10-5

  7. Secondary Anisotropies • Non-Linear Evolution • Weak Lensing • Thermal and Kinetic SZ effect • Etc. • Primary Anisotropies • Tightly coupled Photon-Baryon fluid oscillations • Linear regime of perturbations • Gravitational redshifting Decoupling LSS reionization ~10h-1Mpc 10Gyrs 14Gyrs today

  8. ∆T/T ~ 10-5

  9. Matter constituents at T~3000K • Radiation ~ 20% (r) • Baryons ~ 15% (b) • Dark matter ~ 65% (cdm) • Dark energy ~ 0.000% • Curvature ~ 0.0 ?

  10. Generation of the observable CMB temperature anisotropy at last-scattering surface • Constitutents: baryons+radiation interacting via Thompson scattering + dark matter. • Modes: adiabatic/isocurvature, tensor, growing/decaying • Scale: sound horizon rs • Coherent standing waves • Correlated Effects: • photon energy perturbation + grav.potential • Doppler effect from moving electrons • Coherence – one mode, one random, adds in quadrature. • Effect of massive baryons

  11. Formation of CMB anisotropy at last scattering Adiabatic cosine behaviour ¼ r + ~ Ak cos(k rs) k → 0, dT/T ≠ 0 ΔT/T(k)  2 4 5 K rs

  12. CMB anisotropy at last scattering Amplification of short waves when radiation dominated gravity ¼ r+ ~ f(k) cos(k rs) ΔT/T(k)  2 2 2 k rs

  13. Damping of short waves at last scattering photon diffusion, shear viscosity of plasma, non-instant recombination ¼ r + ~ f(k) cos(k rs) exp(-k2/kD2) ΔT/T(k)  4 5 2 k rs

  14. Doppler effect (movement of scattering electrons) Doppler part of dT/T ~ i Aksin (k rs) ΔT/T(k)  2 4 5 k rs

  15. Effect of baryon mass Offset of ¼ r + - const Decrease of electron velocity i Ak sin (k rs) / sqrt(1+3/4 ρb/ρr) ΔT/T(k)  2 4 5 k rs

  16. Phenomenology of the Angular Power Spectrum Acoustic Oscillations Sachs-Wolfe Damping Drag, Doppler Tensors large <-- scales --> small

  17. Mapping the anisotropy patternonto the sky • Geometry (curvature) of the space • Expansion rate, including presence and dynamical properties of the vacuum energy (quintessence field ?) • But, both mainly affect angular diameter distance, thus degeneracy:  R/rs = l • Extra physics, modifying Cl: • ISW (photon propagation through varying grav.pot (large scales) • Secondary reonization (at z>5) – damping of small scales. Relates physics of CMB to first stars formation

  18. Less well understood, thus more interesting ingredients, relating CMB to fundamental physics • Initial conditions – adiabatic -> inflation – slope, amplitude, potential. Easy to check given theory, less satisfying general case. Until recently, only simplest power-law parameterization was justified by the data quality. With WMAP, situation starts changing. • Generation of gravitational waves generation is a natural outcome of the early Universe. GW contributes to low l, its contribution is model dependent but to measure it would be an ultimate prize – GR support, mapping inflaton potential directly.

  19. Minimal Set of 7 Cosmological Parameters c b, cdm k,  ns, 8 Complex plasma at decoupling b/=0.8 m/=3.5 Geometry of the Universe wQ Initial conditions (inflationary) nt,At/As, broken scale invariance Late-time damping due to reionization Joint pre-WMAP CMB measurements: k= -0.05  0.05 b = 0.022 0.002 ns = 0.95 0.04 cdm = 0.12 0.02

  20. Degeneracies • Angular diameter of the sound horizon • c – 8 as predictedfrom CMB • c – ns • c – gravitational waves • Degeracies are especially limiting on partial data, but some are difficult to break overall • One way – combine CMB data with other experiments, which place limits on different combinations • Another way – use polarization

  21. Cosmic Parameter Near-degeneracies Some parameters are measured better than others. Particular degeneracies correlate some parameters Certain combinations of parameters give same projected power spectrum e.g. geometrical degeneracy. If you don’t constrain h and leave matter components unchanged the peaks are projected onto the same l values.

  22. CMB Polarization • Full description of radiation is by polarization matrix, not just intensity – Stockes parameters, I,Q,U,V • Why would black-body radiation be polarized ? Well it is not in equilibrium, it is frozen with Plankian spectrum, after last Thompson scattering, which is polarizing process. • Because, there is local quadrupole anisotropy of the flux scattered of electron. Thus, P and dT/T are intimately related, second sources first (there is back-reaction as well). • There is no circular polarization generated, just linear – Q,U. Level of polarization ~10% for scalar perturbations, factor of 10 less for tensors. Thus need measurements at dT/T 10-6 – 10-8. • As field – B, E modes (think vectors, but in application to second rank tensor), distinguished by parity.

  23. Why do we learn more from polarization ? • No new physics (parameters) just new window to last scattering which is cleaner, albeit signal is weaker. • Clear signature adiabatic mode. • Grav waves are the only source which produces B-pattern – direct detection of this fundamental physical effect is possible. • Breaking degeneracy between parameters, in particular independent measurement of c

  24. “The Seven Pillars” of the CMB(of inflationary adiabatic fluctuations) • Large Scale Anisotropies • Acoustic Peaks/Dips • Damping Tail • Polarization • Gaussianity • Secondary Anisotropies • Gravity Waves Minimal Inflationary parameter set Quintessesnce Tensor fluc. Broken Scale Invariance

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