TheThe CosmicCosmic MicrowaveMicrowave BackgroundBackground Past,Past, PresentPresent andand FutureFuture

Martin White University of California, Berkeley Lawrence Berkeley National Laboratory

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1 Outline

A brief history of from the cosmic microwave background. – Penzias & Wilson – COBE The current state-of-the-art and what we have learnt. – WMAP3 The near future. – Possible future missions. – Secondary anisotropies, low-z structure – Polarization - the next frontier

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2 In the beginning was Bell Labs

Penzias and Wilson shared half of the 1978 Nobel Prize for the discovery of the cosmic microwave background (CMB) .

Fluctuations are black-body, isotropic and not correlated with any (local) structure in the .

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3 …then there was COBE …

Nobel prize in , 2006, awarded to Mather and Smoot “for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation”

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4 A revolution in our understanding of the Universe

Existence of CMB – One of the pillars of the hot big-bang model. Measurement of the black-body spectrum – T = 2.725 ± 0.001 K, deviations < 10-4 – Sets the temperature scale of the Universe  Only cosmological parameter known to better than 1%! – Rules out significant energy injection below z~107. Measurement of the anisotropy – Shrunk substantially the range of viable cosmological models. – Gravitational instability in a dark dominated Universe formed large-scale structure seen by e.g. 2dF or SDSS. – The fluctuations are of the form predicted by . – The large-scale structure of -time is “simple”. Precise normalization of large-scale structure.

All right. But apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, the fresh water system, and public health . . . What have the Romans ever done for us? Reg, spokesman for the People’s Front of Judea

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5 2003: WMAP reported 1st year data!

This … Became this! Power

Angular scale From .gsfc..gov

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6 Current state-of-the-art

From lambda.gsfc.nasa.gov

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7 Of the “dozen” parameters in our cosmological model:

1 parameter known to better than 1% (2 if you count peak angular scale) 5 parameters known to better than 10% (independently) from the CMB alone.

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8 Cosmological parameters

2 ωm= Ωmh = 0.1277 ± 0.008

-30 3 . ρm= (2.11 ± 0.13) x 10 g/cm 2 ωb= Ωbh = 0.02229 ± 0.0007

-31 3 . ρb= (4.19 ± 0.13) x 10 g/cm δΦ/c2 = (3 ± 0.1) x 10-5

o θA = 0.5952 ± 0.0021 s = (147.8 ± 2.6) Mpc = (4.56 ± 0.08) x 1026 cm

28 dLS = (14.2 ± 0.2) Gpc = (4.38 ± 0.08) x 10 cm

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9 Other inferences

From the narrow first peak we know that whatever “rang the bell” was sharp and of short duration, not a continuous driving. The fluctuations are dominated by large-scale density perturbations (not vorticity modes or gravity waves). The universe was not “weird” at z~103. Inflation is in good shape. – Fluctuations are small, harmonic, Gaussian & adiabatic – Limits on specific models of inflation – e.g. λφ4 inflation is ruled out at ~ 2-3σ . – Tentative detection of departure from scale-invariance (maybe!).

 ns=0.958 ± 0.016 (no running; lambda.gsfc.nasa.gov)

 ns=0.970 ± 0.016 (no running; Huffenberger et al. 2007)

 ns=0.993 ± 0.030 (no running+r; Cortes, Liddle & Mukherjee 2007)

 ns=0.981 ± 0.034 (w/ running+r; Cortes, Liddle & Mukherjee 2007)

See Erikson et al. (2007); Huffenberger et al. (2007) for

revisions to the initially published WMAP ns results.

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10 Polarization

In the presence of anisotropy we expect scattering to generate (linear) polarization. Consequence of electro-magnetic gauge invariance! Polarization provides a prediction, a cross-check and further about conditions at last-scattering and .

Rees (1968) Kaiser (1983) Hu & White (1997)

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11 E- and B-modes

Polarization is made up of two “modes”, referred to as E- and B- modes because of their global parity .

E-modes B-modes

Note that E-modes have no handedness, whereas B-modes do and thus cannot be generated by scalar (density) perturbations.

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12 Polarization: first detection by DASI

Single shaped l-bin Five l-bins 100 6.3σ

) 50 E detection 2 K µ

consistent ( 0

with . E -50 ) Consistent 2 50 K

B µ with zero ( 0 (theory) B -50

) 100 2.9σ 2 Leitch et al., 2005 K µ TE detection ( 0

consistent -100TE with theory 0 200 400 600 800 1000 l (angular scale)

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13 The world compilation Courtesy Lewis Hyatt


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14 The picture from WMAP3


Adiabatic / inflationary peak

Polarization from z~103

Polarization from z~10 Page et al. 2006 Polarization from GWs from z~10?? (Not seen! Upper limit.)

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15 The near (!) future: Planck

Planck is part of ESA’s “Cosmic Visions” program and is currently scheduled for launch in July 2008 along with the Herschel satellite. Planck will be the first sub-mm mission to map the entire sky with mJy sensitivity with resolution better than 10 arcminutes. The enabled by such a mission spans many areas of and cosmology. K) µ Brightness temperature ( 10 Frequency (GHz) 1000

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16 Planck in cartoons

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17 Planck being assembled

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18 Real hardware!!

Final assembly of the Planck satellite and payload in Europe is almost complete.

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19 The orbit

Planck will make its measurements from the Earth- L2 point. It makes a map of the full sky every 6 months.

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20 A full sky map of temperature and polarization

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21 What (we expect) Planck will add

In addition to wider frequency coverage and better sensitivity than WMAP, Planck has the resolution needed to see into the damping tail. It will be the first experiment to make a cosmic limited measurement of the scales around the 3rd and 4th peaks. (4yr) (1yr)

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22 What (we hope) Planck will add

A precise measurement of the E-mode polarization power spectrum and a highly sensitive search for B-modes (from inflation?).

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23 A dramatic advance

Planck will essentially clean up the primary temperature anisotropies and make great inroads on polarization.

Many of the most important book cosmological parameters will

blue be known much better after Planck flies. Planck

Projected WMAP likelihood Projected Planck likelihood on Hubble constant

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24 CMB science

An inroad to inflation – COBE defined the amplitude of the fluctuations: δ ~10-5

– To constrain models need to measure ns and running

 Expect δns~0.03 → 0.007 and δα~0.04 → 0.003 – c.f. WMAP: longer level arm, more spectra – Also break (accidental n-τ) degeneracy with EE

– May be the first measurement of ns<1 – Rule out [?] isocurvature contribution, P(k) features … – Find GW signal [?] and constrain the energy scale of inflation. 2 – Non-Gaussianity (limits on fNL~100 drop to fNL~1: δtot~δlin+fNLδlin )

Constraining , Ωm, h, etc.

– CMB gives: ωm, ωb, θA. Improve constraints by 5-10.

– Currently δD(z=1100) ~ 3% limited by ωm (δωm~ 6%)

– Planck should get δωm~ 0.9%. – In δD(z=1100) ~ 0.2%! Secondary Anisotropies – Highly significant detection of gravitational lensing – Constraints on how the Universe reionized (large & small scales) – Catalog of the most massive clusters of , anywhere in the Universe – Cross-correlation for the clustering of dark energy, massive , …

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25 The CMB “prior”

With WMAP, and certainly after Planck, we will have very precise knowledge of the universe at z~1000. We will have tightly constrained the physical densities of matter and baryons, the amplitude of the fluctuations in the linear phase over 3 decades in length scale and the shape of the primordial power spectrum. Our knowledge of physical conditions and large-scale structure at z~103 will be better than our knowledge of such quantities at z~0! If dark energy is a recent phenomenon, then we can translate this knowledge reliably to intermediate which are currently at the observational frontier.

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26 The real-space z~3 power spectrum

CMB enables us to constrain the high-z matter power spectrum (with lengths measured in meters!) Example: using the WMAP 3yr data constrains Δ2(k) to 7% 7% measurement near near k~0.01/Mpc acoustic peak scale. assuming a basic ΛCDM model. This drops to 3% if τ is controlled for. With Planck this will White ‘06 be a percent level measurement!

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27 Making it to z=0

The in large-scale thus comes from the extrapolation to z=0 and to space. – Growth of fluctuations between z~3 and z=0 depends on dark energy and massive neutrinos (vertical shifts). – Conversion from physical distances (in Mpc) to local intervals (in -1 h Mpc) brings in a dependence on h (horizontal shifts).

Possible running of the spectrum or “warm” components can introduce additional uncertainty on small scales (relevant, for example, for first structures). – The larger lever arm, better sensitivity and excellent polarization sensitivity of Planck will allow us to push to ever smaller scales.

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28 Polarization and the energy scale of inflation

If Planck is successful the temperature power spectrum will be measured to essentially limits over a wide range of frequencies and most of the relevant length scales. – Higher resolution experiments will study “secondary” anisotropies, such as produced by cosmic structures at lower redshift. Planck will provide excellent measurements of polarization on large angular scales, and good measurements on small scales. But we can do better! – Future CMB experiments will focus on measuring the polarization of the CMB to ever higher precision at ever more frequencies. – Ultimate goal is to be limited only by astrophysical foregrounds. – This will characterize the E-modes, detect the B-modes produced by gravitationally lensing the E-modes and (perhaps/hopefully) detect the B-modes produced by gravitational waves created during the epoch of inflation. – These measurements will provide strong constraints on the nature of the fluctuations and any “features” in the primordial spectrum (from inflation?). – A detection of gravity wave induced B-modes from inflation would provide strong constraints on the energy scale of inflation!

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29 A near-future experiment to measure CMB poln QUIET team

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30 Conclusions

The CMB has been revolutionary for our understanding of cosmology. – Combination of experimental achievements, theoretical breakthroughs and heroic data-analysis. WMAP has firmly established an of “precision cosmology”. Planck will provide a dramatic advance in our knowledge of primary and secondary CMB anisotropies. – Constraining the universe at z~1000. – Testing inflation. – Pinning down models of large-scale structure. – Anchoring probes of dark energy. High resolution “secondary anisotropy” experiments are just beginning, and will return data within the year. Measurements of polarization are the next frontier and may constrain the energy scale of inflation.

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31 TheThe EndEnd

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