CMB?

1. Espectro de la RCF 2. Anisotropías de la RCF

CMB anisotropy + +

Anisotropies X=T,E,B X(θ,φ)=Σ lm a lm X Y s lm (θ,φ) spherical harmonics s=0 for T, 2 for Q and U E and B modes have opposite parity

Angular power spectrum a X lm, X=T,E,B C l =Σ m [(a lm X )(a lm Y )*]/(2l+1) spherical harmonics information compression

Use Ripples in CMB to Measure Composition of the Universe The Basic Idea: Hit it and listen to the cosmic sound. – Analogy: Brass and ceramic can be discriminated by hitting them and listening to the sound created by them. – We can use sound waves to determine composition. When CMB was emitted the Universe was a dense and hot soup of photons, electrons, protons, Helium nuclei, and dark matter particles. – Ripples in CMB propagate in the cosmic soup: the pattern of the ripples, the cosmic sound wave, can be used to determine composition of the Universe!

How do we “hear” the cosmic sound from this?

metric perturbations Decomposition into scalar, vector and tensor components Linear cosmological perturbation theory

The cartoon At early times the universe was hot, dense and ionized. Photons and matter were tightly coupled by Thomson scattering. – Short m.f.p. allows fluid approximation: baryon-photon fluid Initial fluctuations in density and gravitational potential drive acoustic waves in the fluid: compressions and rarefactions. A sudden “recombination” decouples the radiation and matter, giving us a snapshot of the fluid at “last scattering”. [harmonic wave]

Approximate Equation System in the Strong Coupling Regime SOUND WAVE!

Cosmic Sound Wave!

It is the nature of things that they are ties to each other. —Chuang-tzu (300BC)