cmb?. 1. espectro de la rcf 2. anisotropías de la rcf
TRANSCRIPT
CMB?
1. Espectro de la RCF
2. Anisotropías de la RCF
CMB anisotropy
Anisotropies
T(θ,φ), Q(θ,φ), U(θ,φ), V(θ,φ)
X=T,E,B
X(θ,φ)=Σlm almX Ys
lm(θ,φ)
spherical harmonics
s=0 for T, 2 for Q and U
E and B modes have opposite parity
Angular power spectrum
T(θ,φ), Q(θ,φ), U(θ,φ), V(θ,φ)
aXlm, X=T,E,B
Cl=Σm [(almX)(alm
Y)*]/(2l+1)
spherical harmonics
informationcompression
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)
It is the nature of things that they are ties to each other. —Chuang-tzu (300BC)