The Future of the CMB

Marc Kamionkowski

(Caltech)

AIU ’08, Tsukuba, 13 March 2008

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14 billionlight-years

CMB that we see originates from edge of observable Universe as it was ~400,000 years after the big bang,~14 billion years ago

Causallyconnectedregion

Observe:•CMB smooth to 1st approximation•Has small fluctuations•BBN accounts for light-element abundances

Can infer:•Primordial density perturbations exist•Have small amplitude on largest scales•Have small amplitude on smallest scales•Have spectrum (in wavenumber k) no steeper than scale invariant

Slow-rollparameters

Inflationaryperturbations:

CMB determination

of the geometry(MK, Spergel, and Sugiyama, 1994)

(flat)

(open)

First test of inflation:Is the Universe flat?

Cl=<|alm|2>T(n)=Σ almYlm(n)

YES!

30 K

BOOMERanG (2002)

Now even more precise from WMAP

Cosmological-parameter determination(Jungman, MK, Kosowsky, Spergel 1996)

WMAP-3:

even better than we expected!!

WHATNEXT???

INFLATION

GEOMETRY SMOOTHNESS STRUCTUREFORMATION

What is Einfl?

STOCHASTIC GRAVITATIONAL WAVE

BACKGROUND with amplitude Einfl2

Detection of ultra-long-wavelength GWs frominflation: use plasma at CMB surface of last scatteras sphere of test masses.

Temperature pattern produced by one gravitational wave oriented in z direction

z

No Gravity Waves

Gravity Waves

Detection of gravitational waves with CMB polarization

Temperature map:

Polarization Map:

Density perturbations have no handedness”so they cannot produce a polarization with a curl

Gravitational waves do have a handedness, so theycan (and do) produce a curl

Model-independent probe of gravitational waves!

(MK, Kosowsky, Stebbins, 1996; Seljak & Zaldarriaga 1996)

“E Mode”

“B mode”

“Curl-free” polarization patterns

“curl” patterns

GWs

Recall, GW amplitude is Einfl2

l2

GWs unique polarization pattern. Is it detectable?

If E<<1015 GeV (e.g., if inflation from PQSB), then polarization far too small to ever be detected.

But, if E~1015-16 GeV (i.e., if inflation has something to do with GUTs), then polarization signal is conceivably detectable by Planck or realistic post-Planck experiment!!!

And from COBE, Einfl<3x1016 GeV

Big news:

If ns=0.95, and ε~η (and no weird cancellation), then ε~0.01, V~(2x1016 GeV)4, and r=T/S~0.1.

I.e., GW background ~ “optimistic” estimates

(e.g., Smith, Cooray,MK, arXiv:0802:1530)

synchrotron 100 GHz

dust 100 GHz

WMAPBICEPQUIET1QUEST (QUaD)PlanckQUIET2

synchrotron 100 GHz

dust 100 GHz

HivonSPIDER

(Kesden, Cooray, MK 2002; Knox, Song 2002)

If GW amplitude small, may need high-resolution T/P maps to disentangle cosmic-shear contribution to curl component from that due to inflationary gravitational waves.

Lensing shifts position on sky:

Where the projected grav potential is

even if there was no primordial curl, withpower spectrum

and so lensing induces a curl

How can we correct for it? T also lensed. Inabsence of lensing,

but with lensing,

We can therefore reconstruct the deflectionangle….

Another possibility to correct for cosmic shear

(Sigurdson, Cooray 2005)

• Use 21-cm probes of hydrogen distribution to map mass distribution between here and z=1100

The CMB: What else is it good for?

WMAP-5: fraction of CMB photonsthat re-scattered after recombination (z~1100) is τ~0.1.

If electrons that re-scattered these CMBCMB photons were ionized by radiationfrom the first stars, then the first starsformed at z=10

Probes of parity violation in CMB

(Lue, Wang, MK 1999)

Might new physics responsible for inflationbe parity violating?TC and TG correlations in CMB are parity violating.Can be driven, e.g., by terms of formduring inflation or since recombination

WMAP search: Feng et al., astro-ph/0601095 Komsatsu et al. (WMAP-5)

High-frequency gravitational waves and the CMB

GWs are tensor modes of perturbations.“Conventional” way to probe GWs: 1) low-l plateau versus peaks 2) B mode polarization

New approach:Small scale GW behave as massless particles. They contribute to the energy density of the Universe.

Limits on gravitational-wave energy density

Smith, Pierpaoli, MK (PRL, 2006)

Particle Decays and the CMBXuelei Chen and MK, PRD 70, 043502 (2004)

L. Zhang et al., PRD 76, 061301 (2007)also, Kasuya, Kawasaki, Sugiyama (2004)

and Pierpaoli (2004)

• Can we constrain dark-matter decay channels and lifetimes from the CMB and elsewhere?

Transparencywindow

Photons absorbed by IGM

IGMoptical depth,temperature,and ionizationfor decaying particle

Ionizationinduced byparticleDecaysaffectsCMB powerspectra

What Else??Inflation predicts distribution of primordialdensity perturbations is Gaussian (e.g., Wang &MK, 2000).

But how do wetell if primordialperturbationswere Gaussian??

In single-field slow-roll inflation,nongaussianity parameter (e.g., Wang-MK 1999): fNL ~ ε (δρ/ρ) ~ 0.01 x 10-5

Will be small!! WMAP now at fNL ~50; Planck to getto fNL ~O(1). So simplest models not to be tested,but alternatives may produce larger fNL .

Φ=φ+ fNL (φ2-<φ2>)

Gravitational potential

Gaussian random field

How do we tell if primordial perturbations were Gaussian??

(1) With the CMB:

T/T

Advantage: see primordial perturbation directlyDisadvantage: perturbations are small

How do we tell if primordial perturbations were Gaussian??

(2) With galaxy surveys:Advantage: perturbations are biggerDisadvantage: gravitational infall induces non-Gaussianity (as may biasing)

Evolved

Primordial

How do we tell if primordial perturbations were Gaussian??

(3) With abundances of clusters (e.g., Robinson, Gawiser & Silk 2000) or high-redshift galaxies (e.g., Matarrese, Verde & Jimenez 2000):

Rare objectsform here

How do we tell if primordial perturbations were Gaussian??

(4) With distribution of cluster sizes (Verde, MK, Mohr & Benson, MNRAS, 2001):

Broader distribution of >3 peaks leads to broaderformation redshift distributionand thus to broader sizedistribution

How do we tell if primordial perturbations were Gaussian??

How do these different avenues compare?

For just about any nonGaussianity with long rangecorrelations (e.g., from topological defectsor funny inflation), CMB> LSS (Verde, Wang,Heavens & MK, 2000).

Cluster and high z abundances do betterat probing nonGaussianity from topologicaldefects than CMB/LSS, while CMB remainsbest probe of that from funny inflation(Verde, Jimenez, Matarrese & MK, MNRAS 2001).

Is the Universe Statistically Isotropic? Pullen and MK, PRD (2007); Ando and MK PRL (2008)

Inflation usually predicts primordial perturbations are statistically isotropic---they have no preferred direction: Power spectrum P(k) function of wavenumberk magnitude only; not its direction.

But what if this were violated (e.g., Ackerman, Carroll,Wise,

2007)? What if we had a power spectrum that depended onthe direction of k?

Statisticallyisotropic

E.g.,a powerquadrupole

If SI is violated:

And is straightforward to calculate theDll’ given P(k).

Departures from SI correlate different alm’s.

Pullen-MK: minimum-variance estimatorsfor the ξlml’m’ and also the gLM. E.g., WMAP sensitive to g20~0.02 and Planck to g20~0.005 (1σ).

Ando-MK: nonlinear evolution ofprimordial anisotropic power: Pprim(k) Ptoday(k)

required to search galaxy surveys for SI departures.

Pullen-Hirata now testing SI with SDSS/WMAP

Direct Detection of Inflationary Gravitational Waves?(T. L. Smith, MK, Cooray, PRD 2006;

see also Efstathiou-Chongchitnan and Smith-Peiris-Cooray)

Mission concept studies:

•NASA: Big-Bang Observer (BBO)•Japan: Deci-Hertz Gravitational-Wave Observatory (DECIGO)

seek to detect directly inflationary gravitational-wave background at ~0.1-Hz frequencies

“power-law” “chaotic”

“hybrid”

“symmetry-breaking”

Survey some “toy” models for inflation:

Ten

sor-

to-s

cala

r ra

tio

r

Power-law

chaotic

Symmetrybreaking

chaotic

Dark Matter, the Equivalence Principle, and Dwarf Galaxies

Work done with Mike Kesden,

PRL 97, 131303 (2006) [astro-ph/0606566],

PRD 74, 083007 (2006) [astro-ph/0608095]

For dessert: something completely different…..

Rotation

speed

observed

disk

8.5 kpc

3-5 kpc

Local dark-matterdensity: ~0.4 (GeV/c2)/cm3

Velocity dispersion: v ~ 300 km/sec

220 km/sec

But does dark matter fall same wayin gravitational field? Does the force law,

hold for dark matter as well? And if how would we know?

Instead, consider tidal streams of Sagittarius dwarf:

•Sgr is DM dominated so acts as DM tracer of MilkyWay potential, while stripped stars act as baryonictracers.•Streams are long-lived and now well-observed with2MASS and SDSS•Detailed simulations compared with observationsalready provide remarkably precise constraints to Sgrmass, M/L, orbit, and Milky Way halo (e.g., Law,Johnston, Majewski 2005)

Maj

ewsk

i et a

l. 20

03

Where do tidal streams come from?

MW

Sgr

trajectory

Leading tail

Trailingtail

R

M=mass

m=mass

r

Where do tidal streams come from?

MW

Sgr

trajectory

Leading tail

Trailingtail

R

M=mass

m=mass

r

Conclusions

• Conservative “by-eye” comparison with observation of roughly equal leading and trailing stream constrains DM force law to be within ~10% of that for baryons

Summary

• CMB provides ever increasing evidence for inflation• Departure from scale invariance significant, if real,

provides additional motivation for pursuing IGWs• Cosmic shear of CMB provides exciting new target; room

for theoretical and data-analysis work• Can begin to test Gaussianity of primordial perturbations• Can begin to test validity of statistical-isotropy prediction• Theorists need to be more imaginative: what else can we

do with the CMB? Where do we go next?