Cosmic Microwave Cosmic Microwave Background Background Basic Physical Process: Why so Important for Cosmology Naoshi Sugiyama Naoshi Sugiyama Department of Physics, Nagoya University Institute for Physics and Mathematics of the Universe, Univ. Tokyo
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Naoshi Sugiyama- Cosmic Microwave Background Basic Physical Process: Why so important for cosmology
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Naoshi SugiyamaNaoshi SugiyamaDepartment of Physics, Nagoya University
Institute for Physics and Mathematics of the Universe, Univ. Tokyo
Before Start!GCOE @ Nagoya U.
• We have a program of Japanese government, Global Center of Excellence Program (GCOE). This Global COE recruits graduate students. For those who are interested in doing their PhD work on particle physics, cosmology, astrophysics, please contact me! We are also planning to have a winter school in Feb. for dark matter and dark energy.
• If the Universe was in the thermal equilibrium, photon distribution must be Planck distribution (Black Body)
• Energy Density of Photons is
4)1( z
Why Information beyond Horizon?
• Here we assume matter dominant, a is the scale factor, H is the Hubble parameter.
Horizon Size at recombination
• Using the same formula in the previous page, but insert z=0, instead z=1100. Here we ignore a dark energy contribution in the Hubble parameter
Mpc)(6000
Mpc)1100()(180)(2/12
2/12/120
h
htd
M
MH
Horizon Size at present
• Angular size of the Horizon at z=1100 on the Sky can be written as
degree7.1rad030.0)(/)( 0 tdtd Hrecc
HC.f. angular size of the moon is 0.5 degree
dHc(z=1100)
dH(z=0)
1.7degree
There must not have any causal contact beyond HorizonSame CMB temperature
Univ. should expand faster than speed of light
Angular Size of the Horizon at z=1100
Horizon Problem
Inflation
§2. Anisotropies
• As a first approximation, CMB is almost perfect Black Body, and same temperature in any direction (Isotropic)
• It turns out, deviation from isotropy, i.e., anisotropy contains rich information
• Two anisotropies
– Spectral Distortion
– Spatial Anisotropy
2cm
kTndly
e
eTe
1exp
8 3
3
kThc
hf
Extremely Good Black Body Shape in average
Observation by COBE/FIRAS
2-1. Spectral Distortion
y-distortion y < 1.5x10y < 1.5x10-5-5
-distortion ||| < 9x10| < 9x10-5-5
Sunyaev-Zeldovich Effecty-distortion
• Caused by: Thermal electrons scatter off photons
• Photon distribution function: move low energy photons to higher energy
frequency
Distribution function
• distort Black Body low freq: lower temp high freq: higher temp no change: 220GHz
higher higher lower lower
SZ Effectf: photon distribution function
Energy Transfer: Kompaneets Equation
y-parameter:
k: Boltzmann Const, Te: electron temperature, me: electron mass, ne: electron number density, T: Thomson Scattering Cross-section , : Optication depth
Solution of the equation
low freq. limit: x<<1high freq. limit: x>>1
fPL: Planck distribution
yff 2/ 2/ yxff
decrementincrement
f/f=T/T in low frequency limit (depend on the definition of the temperature)
• SZ Effect Provides Information of– Thermal History of the Universe– Thermal Plasma in the cluster of galaxies
CMBPhoton
Hot ionized gas in a
cluster of galaxies
Q: typically, gas within a big cluster of galaxies is 100 million K, and optical depth is 0.01. What are the values of y and temperature fluctuations (low frequency) we expect to have?
http://astro.uchicago.edu/sza/overview.html
•Clusters provide SZ signal. •However, in total, the Universe is filled by CMB with almost perfect Planck distribution
200 sigma error-bars
COBE/FIRAS
wavelength[mm]
frequency[GHz]
inte
nsit
y[M
Jy/s
tr]
2.725K Planck distribution
Cosmic Microwave Background
• Direct Evidence of Big Bang– Found in 1964 by Penzias & Wilson– Very Precise Black Body by COBE in 1989 (J.Mather)
John Mather Arno Allan Penzias
Robert Woodrow Wilson
2-2. Spatial Anisotropies 1976: Dipole Anisotropy was discovered
3mK peculiar motion of the Solar System
to the CMB rest frame
Annual motion of the earth is detected by COBE:the Final proof of heliocentrism
Primordial Temperature Fluctuations of Cosmic Microwave Background• Found by COBE/DMR in 1992 (G.Smoot),
measured in detail by WMAP in 2003
• Structure at 380,000 yrs (z=1100)– Recombination epoch of Hydrogen atoms
• Missing Link between Inflation (10-36s) and Present (13.7 Billion yrs)
• Ideal Probe of Cosmological Parameters – Typical Sizes of Fluctuation Patters are Theoretically
Known as Functions of Various Cosmological Parameters
COBE 4yr data
COBE & WMAP
George Smoot
Temperature Anisotropies:Origin and Evolution
Origin: Hector de Vega’s Lecture
• Quantum Fluctuations during the Inflation Era
10-36[s]
• 0-point vibrations of the vacuum generate inhomogeneity of the expansion rate, H
• Inhomogeneity of H translates into density fluctuations
Temperature Anisotropies:Origin and Evolution
Evolution
• Density fluctuations within photon-proton-electron plasma, in the expanding Universe
• Dark matters control gravityPhoton:
Distribution function Boltzmann EquationProton-Electron
Fluid coupled with photons through Thomson Scattering Euler Equation
Dark MatterFluid coupled with others only through gravity Euler Eq.
Boltzmann EquationC: Scattering Term
Perturbed FRW Space-Time
Temperature Fluctuations
Optical Depth Anisotropic Stress
C
Fluid Components:
Proton-electron
Dark Matterdm dm
dmdm
Numerically Solve Photon, Proton-Electron and dark matter System in the Expanding Universe
Boltzmann Code, e.g., CMBFAST, CAMB
Scale Factor
Flu
ctua
tion
s
Long Wave Mode
Scale Factor
Flu
ctua
tion
s
Short Wave Mode
§3. What can we learn from spatial anisotropies?
Observables
1. Angular Power spectrum– If fluctuations are Gaussian, Power spectrum (r.m.s.)
contain all information
2. Phase Information– Non-Gaussianity– Global Topology of the Universe
3. Polarization– Tensor (gravitational wave) mode– Reionization (first star formation)
3-1. Angular Power Spectrum• Cl
T/T(x)
Angular Power Spectrum• <|T/T(x)|2>=(2l+1)Cl/4dl (2l+1)Cl/4
= (dl/l) l(2l+1)Cl/4• Therefore, logarithmic interval of the temperature power in
l is l(2l+1)Cl/4 or often uses
• l corresponds to the angular size l=/=180[(1 degree)/]
C.f. COBE’s angular resolution is 7 degree, l<16
Horizon Size (1.7 degree) corresponds to l=110
l(l+1)Cl/2
COBE
180 10 1 0.1Angular Scale
Horizon Scale at z=1100(1.7degree)
Different Physical Processes had been working on different scalesDifferent Physical Processes had been working on different scales
3-2. Physical Process
• Gravitational Redshift on Large Scale
– Sachs-Wolfe Effect
• Acoustic Oscillations on Intermediate Scale
– Acoustic Peaks
• Diffusion Damping on Small Scale
– Silk Damping
Individual Process
(a) Gravitational RedshiftGravitational Redshift: large scales
What is the gravitational redshift?
• Photon loses its energy when it climbs up the potential well: becomes redder
• Photon gets energy when it goes down the potential well : becomes bluer
Surface of the earth
h
h-mgh= h-(h /c2)gh = h(1-gh/c2) h’h
1)Lose energy when escape from gravitational potential : Sachs-Wolfe redshift
grav. potential at Last Scattering Surface
12
2)Get (lose) energy when grav. potential decays (grows)
: Integrated Sachs-Wolfe, Rees-Sciama
E=|1-2| blue-shift
Individual Process
(a) Gravitational RedshiftGravitational Redshift: large scales
Comments on Integrated Sachs-Wolfe Effect (ISW)• If the Universe is flat without dark energy (Einstein-de Sitter Univ.), potential stays constant for linear fluctuations: No ISW effect
ISW probes curvature / dark energy•Curvature or dark energy can be only important in very late time for evolution of the Universe
Since late time=larger horizon size, ISW affects Cl on very small l’s
•However, when the universe became matter domination from radiation domination, potential decayed! This epoch is near recombination
Optical Depth • After recombination, the universe is really
transparent?
• Answer: NO!
It is known z<6, the inter-galactic gases are ionized from observations Free Electrons
• Stars and AGN (quasars) produced ionized photons, E>13.6eV
The Universe gets partially Clouded!
Tendt Define Optical Depth of Thomson Scattering as
Temperature Fluctuations are Damped as
e // NoDampingTTTT
can be a probe of the epoch of reionization (first star formation).
(Polarization is very important clue for reionization)
Recombination400,000yr
Big Bang 13.7Byr.
Ionized gas
Scattering at recombination Scattering at recombination
Recombination
Big Bang
Star Formation
Ionized Gas Ionized gas
Some photons last scattered at the late epoch Some photons last scattered at the late epoch
Temperature Fluctuations Damped away on the Temperature Fluctuations Damped away on the scale smaller than the horizon at reionizatoionscale smaller than the horizon at reionizatoion
Time Variation of Fundamental ConstantsTime Variation of Fundamental Constants
= -0.72±0.1810-5
0.5 < z < 3.5
QSO absorption line
Webb et al.
Influence on CMB
Thomson Scattering:
d/dtxeneT
: optical depth, xe: ionization fraction
ne: total electron density, T: cross section
If is changed
1) T2 is changed
2) Temperature dependence of xe i.e., temperature
dependence of recombination preocess is modified
For example, 13.6eV = 2mec2/2 is changed!
If If was smaller, recombination became later was smaller, recombination became later
If If =±5%, =±5%, z~100z~100
=0.05
=-0.05
Flat, M=0.3, h=0.65, Bh2=0.019
Ionization fraction
Temperature Fluctuation
Peaks shift to smaller l for smaller since the Universe was larger at recombination
=0.05
=-0.05
Varying Varying G G and CMB anisotropiesand CMB anisotropies
• Brans-Dicke / Scalar-Tensor Theory
G 1/ (scalar filed)
: G may be smaller in the early epoch
BUT, it’s not necessarily the case
in the early universe
• Stringent Constraint from Solar-system
: must be very close to General Relativity
GG00/G/G
If G was larger in the early universe,
the horizon scale became smaller
c/H = c(3/8G)
Peaks shift to larger Peaks shift to larger ll
Nagata, Chiba, N.S.
larger G
We have hope to determine We have hope to determine
cosmological parameters together with cosmological parameters together with
the values of fundamental quantities, the values of fundamental quantities,
i.e., i.e., , , G G
and the nature of elementary particles and the nature of elementary particles
at the recombination epoch at the recombination epoch
by measuring CMB anisotropies by measuring CMB anisotropies
Angular Power Spectrum is sensitive to
• Values of the Cosmological Parameters Mh2
Bh2
– h
– Curvature K
– Initial Power Spectral Index n
• Amount of massless and massive particles
• Fundamental Physical Parameters
Comparison with Observations and set constraints
Bayesian analysisMarkov chain Monte Carlo (MCMC)
Question
• increase Bh2 higher peak, decrease Mh2 higher peak. How do you distinguish these two effects?
For that, calculate l(l+1)Cl /2 for Bh2=0.02 and Mh2 =0.15 (fiducial model). Then increase Bh2 to 0.03, and find the value of Mh2 which provides the same first peak height as the fiducial model. And compare the resultant l(l+1)Cl /2 with the fiducial model.
h=0.7, n=1. flat, no dark energy
• Gaussian v.s. Non-Gaussian– If Gaussian, angular power spectrum contains all
information– Inflation generally predicts only small non-Gaussianity
due to the second order effect
• Rare Cold or Hot Spot?
• Global Topology of the Universe
3-4. Beyond Power Spectrum: Phase
Non-GaussianityNon-Gaussianity
Fluctuations generated during the inflation Fluctuations generated during the inflation epochepoch Quantum OriginQuantum Origin Gaussian as a first approximationGaussian as a first approximation
(x)(x)(((x)-(x)-)/)/
(x)0
How to quantify non-Gaussianity
• In real space– Skewness
– Kurtosis
How to quantify non-Gaussianity• In Fourier Space
– Bispectrum
Fourier Transfer of 3 point
correlation function
In case of the temperature angular spectrum,
– Trispectrum
Wigner 3-j symbol
Bispectrum• If Gaussian, Bispectrum must be zero
• Depending upon the shape of the triangle, it describes different nature– Local
– Equilateral
Three torus universe Circle in the sky
Global Topology of the Universe
CMB sky in a flat three torus universe
Cornish & Spergel PRD62 (2000)087304
Angular Power Spectrum is sensitive to
• Values of the Cosmological Parameters Mh2
Bh2
– h
– Curvature K
– Initial Power Spectral Index n
• Amount of massless and massive particles
• Fundamental Physical Parameters
Comparison with Observations and set constraints
Bayesian analysisMarkov chain Monte Carlo (MCMC)
ONE NOTE!ONE NOTE!
m= 1- K-
= 0
Degenerate contour
flat
Efstathiou and Bond
close to the close to the flat geometryflat geometryBUT not quite!BUT not quite!
Geometrical Degeneracy
Identical baryon and CDM density: Bh2, Mh2
Identical primordial
fluctuation spectra Identical Angular
Diameter R(, K)
Should Give IdenticalPower SpectrumShould Give IdenticalPower Spectrum
Projection from LSS to l
[iii] open <1: Geodesic effect
smaller pushes peakes to
large l
[ii] & <1: Further LSS
smaller pushes peaks to
large l
[i] flat =1
Almost degenerate models
For same value of R
Degenerate line
h=0.5
What we can determine from CMB power spectrum is
BBhh22, , mmhh22, ,
degenerate line (nearly curvature)degenerate line (nearly curvature)
Difficult to measure
curvature itself and , , mm, , B B directlydirectly
Question: Generate Cl’s on this degenerate line for M=0.3, 0.5, 0.6 and make sure they are degenerate.
§3. §3. Observations and ConstraintsObservations and Constraints
COBECOBE Clearly see large scale (low Clearly see large scale (low ll ) tail ) tail angular resolution was too bad to resolve peaksangular resolution was too bad to resolve peaks
Balloon borne/Grand Base experimentsBalloon borne/Grand Base experiments Boomerang, MAXMA, CBI, Saskatoon, Python, OVRO, Boomerang, MAXMA, CBI, Saskatoon, Python, OVRO,
etc etc See some evidence of the first peak, even in Last See some evidence of the first peak, even in Last
Century!Century! WMAPWMAP
CMB observations
by 1999
COBE & WMAP
1st yr
3 yr
WMAP WMAP ObservationObservation
WMAP Temperature Power Spectrum
• Clear existence of large scale Plateau
• Clear existence of Acoustic Peaks (up to 2nd or 3rd )
• 3rd Peak has been seen by 3 yr data
Consistent with Consistent with
Inflation and Cold Dark Matter ParadigmInflation and Cold Dark Matter Paradigm
One Puzzle:
Unexpectedly low Quadrupole (l=2)
Measurements of Cosmological Measurements of Cosmological Parameters by WMAPParameters by WMAP
Finally Cosmologists Have the Finally Cosmologists Have the “Standard Model!”“Standard Model!”
But…But… 72% of total energy/density is unknown: Dark 72% of total energy/density is unknown: Dark
EnergyEnergy 23% of total energy/density is unknown: Dark 23% of total energy/density is unknown: Dark
MatterMatter
Dark Energy is perhaps a final piece of the puzzle for cosmology
equivalent to Higgs for particle physics
Dark EnergyDark Energy
How do we determine How do we determine =0.76 or 0.72? =0.76 or 0.72?
Subtraction!: Subtraction!: = 1- = 1- MM - - KK
Q: Can CMB provide a direct probe of Dark Energy?Q: Can CMB provide a direct probe of Dark Energy?
Dark EnergyDark Energy CMB can be a unique probe of dark energyCMB can be a unique probe of dark energy
Temperature Fluctuations are generated by the Temperature Fluctuations are generated by the growth (decay) of the Large Scale Structure (z~1)growth (decay) of the Large Scale Structure (z~1)
Integrated Sachs-Wolfe Effect
1
2
Photon gets blue Shift due to decayE=|1-2|
Gravitational Potential of Structure decays due to Dark Energy
CMB as Dark Energy ProbeCMB as Dark Energy Probe
Integrated Sachs-Wolfe Effect (ISW)Integrated Sachs-Wolfe Effect (ISW) Induced by large scale structure formationInduced by large scale structure formation Unique Probe of dark energy: dark energy slows down the Unique Probe of dark energy: dark energy slows down the
growth of structure formationgrowth of structure formation Not dominant, hidden within primordial fluctuations Not dominant, hidden within primordial fluctuations
generated during the inflation epochgenerated during the inflation epoch
Cross-Correlation between CMB and Large Scale Cross-Correlation between CMB and Large Scale StructureStructure
Only pick up ISW (induced by structure formation)Only pick up ISW (induced by structure formation)
Various Samples of CMB-LSS Cross-Correlation as a function of redshift
Measure w!w=-0.5w=-1w=-2
LessThan 10min
Cross-Correlation between CMB Cross-Correlation between CMB and weak lensingand weak lensing
Weak lensingWeak lensing Distortion of shapes of galaxies due to the Distortion of shapes of galaxies due to the
gravitational field of structuregravitational field of structure Can extend to small scalesCan extend to small scales
Non-Linear evolution of structure formation on small scales
evolution is more rapid than linear evolution rapid evolution makes potential well deeper deeper potential well: redshift of CMB
Gravitational Potential of Structure evolves due to non-linear effect
Large Scale: Blue-ShiftLarge Scale: Blue-Shift Correlated with Lens Correlated with Lens Small Scale: Red-Shift Small Scale: Red-Shift Anti-Correlated Anti-Correlated
Cross-Correlation between CMB & Lensing
l10 100 1000 10000
=0.95, 0.8, 0.74, 0.65, 0.5, 0.35, 0.2, 0.05,
Nishizawa, Komatsu, Yoshida, Takahashi, NS 08
positive
negative
Future experiments (CMB & Large Scale Structure) will reveal the dark energy!
What else can we learn about What else can we learn about fundamental physics from fundamental physics from
WMAP or future Experiments?WMAP or future Experiments? Properties of NeutrinosProperties of Neutrinos
Numbers of NeutrinosNumbers of Neutrinos Masses of NeutrinosMasses of Neutrinos
Fundamental Physical ConstantsFundamental Physical Constants Fine Structure ConstantFine Structure Constant Gravitational ConstantGravitational Constant
Constraints on Neutrino PropertiesConstraints on Neutrino Properties
Change NChange Neffeff or m or m modifies the peak heights modifies the peak heights
and locations of CMB spectrum.and locations of CMB spectrum.
Neutrino Numbers Neutrino Numbers Neff and mass m
Measure the family number at z=1000
CMB Angular Power SpectrumTheoretical Prediction
For Neutrino Mass, CMB with Large Scale Structure Data provide stringent limit since Neutrino Components prevent galaxy scale structure to be formed due to their kinetic energy
Cold Dark Matter Neutrino as Dark Matter(Hot Dark Matter)
Numerical Simulation
Constraints on mConstraints on m and N and Neffeff
WMAP 3yr Data paper by Spergel et al.WMAP 3yr Data paper by Spergel et al.
WMAP 5yr Data paper by Komatsu et al.WMAP 5yr Data paper by Komatsu et al.
CL)%68(5.14.4N
CL)0.66eV(95%
eV(95%CL)5.1
m WMAP aloneWMAP+SDSS(BAO)+SNWMAP+BAO+SN+HST
Constraints on Fundamental Constraints on Fundamental Physical ConstantsPhysical Constants
There are debates whether one has seen variation There are debates whether one has seen variation of of in QSO absorption lines in QSO absorption lines
Time variation of Time variation of affects on recombination affects on recombination process and scattering between CMB photons and process and scattering between CMB photons and electronselectrons
GG can couple with Scalar Field (c.f. Super can couple with Scalar Field (c.f. Super String motivated theory)String motivated theory)
Alternative Gravity theory: Brans-Dicke Alternative Gravity theory: Brans-Dicke /Scalar-Tensor Theory/Scalar-Tensor Theory G G 1/1/ (scalar filed)(scalar filed) G G may be smaller in the early epochmay be smaller in the early epoch
WMAP data set constrain: |WMAP data set constrain: |G/G|<0.05 (2G/G|<0.05 (2) ) ((Nagata, Chiba, N.S.)Nagata, Chiba, N.S.)
Gravitational Constant Gravitational Constant GG
Phase is the IssuePhase is the Issue
Power Spectrum is OKPower Spectrum is OK How about more detailed structureHow about more detailed structure
Alignment of low multipolesAlignment of low multipoles Non-GaussianityNon-Gaussianity Cold SpotCold Spot Axis of Evil Axis of Evil
Tegmark et al.
• Cleaned Map (different treatment of foreground)
• Contribution from Galactic plane is significant
& obtain slightly larger quadrupole moment.
• alignment of quadrupole and octopole
towards VIRGO?
Recent Hot Topics: Non-Recent Hot Topics: Non-GaussianityGaussianity
Fluctuations generated during the inflation Fluctuations generated during the inflation epochepoch Quantum OriginQuantum Origin Gaussian as a first approximationGaussian as a first approximation
(x)(x)(((x)-(x)-)/)/
(x)0
Non Gaussianity from Second Non Gaussianity from Second Order Perturbations of the Order Perturbations of the
Very Tiny Effect: Fancy analysis (Bispectrum etc) starts to reveal non-Gaussianity?
Komatsu et al. WMAP 5 yr.
Cold SpotCold Spot
Using Wavelet analysis for skewness and Using Wavelet analysis for skewness and kurtosis, Santander people found cold spotskurtosis, Santander people found cold spots
Kurtosis Coefficient Only 3-sigma away
This cold spot might be induced by a Super-Void due to ISW since Rudnick et al. claimed to find a dip in NVSS radio galaxy number counts in the Cold Spot.Super Void: One Billion light yr size Typical Void: *10 Million light yr size
What We expect from PLANCKWhat We expect from PLANCK More Frequency CoverageMore Frequency Coverage
Better Estimation of Foreground Emission (Dust, Synchrotron Better Estimation of Foreground Emission (Dust, Synchrotron etc)etc)
Sensitivity to the SZ EffectSensitivity to the SZ Effect Better Angular ResolutionBetter Angular Resolution
Go beyond the third peak, and even reach Silk Damping: Go beyond the third peak, and even reach Silk Damping: Much Better Estimation of Cosmological Parameters, and Much Better Estimation of Cosmological Parameters, and sensitivity to the secondary effect. sensitivity to the secondary effect.
PolarizationPolarization Gravitational Wave: Probe InflationGravitational Wave: Probe Inflation Reionization: First Star FormationReionization: First Star Formation