The Einstein Inflation Probe:Mission Concept Study

Gary Hinshaw, NASA/GSFCMay 12, 2004 Beyond Einstein @ SLAC

“Einstein's equations didn't have a solution that described a universe that was unchanging in time. … he fudged the equations by adding a term called the cosmological constant... The repulsive effect of the cosmological constant would balance the attractive effect of matter and allow for a universe that lasts for all time.”

---Stephen Hawking

ALBERT EINSTEIN

TIME MAGAZINE“PERSON OF THE

CENTURY”

1916: Einstein Shows How Gravity Works

Einstein applied the General Theory of Relativity to the Universe as a whole:

• Future collapse or expand forever• Static Universe (Einstein’s requirement)

The Evolution of the Universe

Early universe remarkably uniform,Current universe is not…

HOW DIDTHIS HAPPEN?

Inflation?... Cyclic model?... (Beyond Einstein)

Beyond Einstein - The Einstein Probes

• NASA/NSF/DOE are planning a line of 3 “Einstein Probe” missions:– A mission to study the dark energy, jointly with DOE, the

“Joint Dark Energy Mission” (JDEM) a.k.a. SNAP.– A survey mission to find black holes in the nearby universe,

the “Black Hole Finder”.– A mission to measure the polarization of the CMB to search

for gravity waves from inflation, the “Inflation Probe” or CMBPOL.

• NASA issued an AO soliciting mission concept studies for each of these missions. In November 2003, several groups were selected to undertake studies.

• Three groups will study the Inflation Probe mission. Their goals are to define the mission requirements for sensitivity, sky coverage, angular resolution, frequency coverage, and the key experimental technologies.

The Concept Study Team

• Chuck Bennett (GFSC)• Mark Devlin (U. Penn)• Dale Fixsen (GSFC)• Gary Hinshaw (GSFC, PI)• Wayne Hu (U. Chicago)• Kent Irwin (NIST/Boulder)• Norm Jarosik (Princeton)• Alan Kogut (GSFC)• Arthur Kosowsky (Rutgers)• Michele Limon (GSFC)• Steve Meyer (U. Chicago)• Amber Miller (Columbia)• Harvey Moseley (GSFC)• Barth Netterfield (U. Toronto)

• Barth Netterfield (U. Toronto)• Angelica Oliviera-Costa (U.

Penn)• Lyman Page (Princeton)• John Ruhl (Case Western)• Uros Seljak (Princeton)• David Spergel (Princeton)• Suzanne Staggs (Princeton)• Max Tegmark (U. Penn)• Bruce Winstein (U. Chicago)• Ed Wollack (GSFC)• Ned Wright (UCLA)• Matias Zaldarriaga (Harvard)• Cliff Jackson (GSFC)

Why the Inflation Probe?

• The B mode signal in CMB polarization (at l<100) is produced by gravity waves left over from inflation. This signal is the only current observational handle we have on physics at the 1016 GeV scale -- 12 orders of magnitude beyond the LHC.

• A measurement of the l<100 B mode signal would directly measure the energy scale of inflation and probe the fluctuation spectrum. It is also a test for alternate models of inflation (e.g., the cyclic universe).

• CMB polarization acts as a filter on cosmological processes. It allows one to probe directly the decoupling epoch, the matter power spectrum (through gravitational lensing), the ionization history, and cosmological parameters.

(lensing)

TT

EE

BB

r=0.1

r=0.01

(gravity waves)

BB

10 100 1000

0.01

0.1

1

10

100

Multipole l

T =

[l(l+

1)Cl/

2π]1/

2 [µ

K]

TE

CMB Polarization

DASI

TT - temperature from scalar and tensor modes

TE - temperature × polarization covariance

EE – “gradient” polarization from scalar & tensor modes

BB – “curl” polarization from tensor modes (only)

DASI EE,

2002

(r limit→BB)

E mode & B mode Polarization

• Polarization decomposable into E mode (gradient) and B mode (curl) components.

• Tensor fluctuations produce both E and B mode components.

• Scalar fluctuations produce only E mode component (except for transformation by gravitatiuonal lensing).

• B modes directly probe gravity waves.

Q > 0 U = 0 Q < 0 U = 0

Q = 0 U < 0 Q = 0 U > 0

Inflation Probe Sensitivity

• One goal of the mission concept study is to define the mission requirements for sensitivity. Roughly:

– The amplitude of B mode polarization follows:

∆TBB ~ r1/2 ~ E2infl

– The power in B mode polarization follows:

(∆TBB )2 ~ Ptensor(k)/Pscalar(k) ~ r ~ E4infl

• “Inflationists” anticipate r ~ 0.01

• The current limits are r<0.9 (95% cl) at k=0.002/Mpc (l~10) from WMAP (Spergel et al.), and r<0.5 (95% cl) at k=0.05/Mpc from WMAP+SDSSS (Tegmark et al.)

• To reach r~0.01, require >~100 sensitivity of WMAP (see later).

• If the energy scale of inflation is low (r<<0.01), the Inflation Probe could rule out inflation occurring at the GUT-scale!

Sensitivity Advances

WMAP

2001

×60

>×20

Planck

~2007

Inflation Probe

COBE

1989

×??

Detector Development: History

COBE FIRAS1 pixel, handmade

KAO spectrometer24 pixels, handmade

KAO, SHARC I24 pixels, micromachined

SHARC II on CSO: 12x32= 384 pixels Largest array in operation

SCUBA-2: 4000 pixels in quadrantsMultiplexer behind detectors

WMAP (Handmade) Microwave Receivers

10 “Differencing Assemblies”

4 @ 94 GHz W-band

2 @ 61 GHz V-band

2 @ 41 GHz Q-band

1 @ 33 GHz Ka-band

1 @ 23 GHz K-band

Jarosik et al. (2003) ApJS, 145, 413Jarosik et al. (2003) ApJS, 148, 29

Foreground Emission

• Polarized foreground emission arises from our galaxy. The signal from our galaxy is currently poorly known, but it is likely comparable to or larger than the gravity wave signal over most of the sky.

• Foreground emission has both E and B mode symmetry.

• Multiple frequencies are necessary to discriminate CMB emission from galactic foreground emission. Unlike the temperature case, modeling and subtracting polarized foreground emission will be necessary.

• Foreground contamination also results from the conversion of primordial E mode signal to B mode signal by gravitational lensing.

• If the lensing contamination not cleaned, it sets a lower detection limit on r of 10-4 at l~100 (the recombination peak) and 10-5 at l~10 (the reionization peak).

Temperature Foreground Spectra

Bennett et al. (2003) ApJS, 148, 97

• WMAP foreground estimates from 1st year temperature data (WMAP observing bands shown in grey)

• CMB dominates foregrounds over most of the sky

• Free-free emission is unpolarized

• Key question: what is polarization fraction of foregrounds relative to B-mode CMB?

• WMAP and other polarization data will be very helpful in guiding our study of foregrounds.

Projected Lensing Foreground (Green)

10 100 1000

0.01

0.1

1

10

100

Multipole l

T =

[l(l+

1)Cl/

2π]1/

2 [µ

K]

Projected Galactic Foreground (Dust/Synch)

10 100 1000

0.01

0.1

1

10

100

Multipole l

T =

[l(l+

1)Cl/

2π]1/

2 [µ

K]

Angular resolution

• The angular resolution required of the Inflation Probe is a major topic of the mission concept study.– High resolution permits more thorough cleaning of the B-

mode signal due to gravitational lensing → better signal to noise at low l

– High resolution is a major cost driver for a space mission!– Concept Study must perform a careful trade study of the

cost-benefit of high angular resolution:• High resolution optical coupling vs. high throughput• Thermal loading with large optics• Spacecraft attitude control requirements/costs• Data rate requirements/costs

Noise Floor for “Strawman I”

10 100 1000

0.01

0.1

1

10

100

Multipole l

T =

[l(l+

1)Cl/

2π]1/

2 [µ

K]

675 background limiteddetectors @ 3 frequencies

Noise Floor for “Strawman II”

10 100 1000

0.01

0.1

1

10

100

Multipole l

T =

[l(l+

1)Cl/

2π]1/

2 [µ

K]

2100 background limiteddetectors @ 3 frequencies

Control of Systematic Errors

• Control of systematic errors is critical to the success of any CMB polarization measurement.

• A key element in rejecting systematic errors is to modulate the signal on many different time scales. The efficiency of different modulation schemes must be assessed.

• It is crucial to verify in flight that systematic effects have been reduced to acceptable levels.

• The most sensitive detectors (e.g. bolometers) are power detectors. Any effect that leads to a difference in power can be confused with a polarization signal, e.g. bandpass mismatch, far side-lobe pick-up, higher order beam effects, etc.

• The gain of the system has to be stable on the time scale that one can measure it in flight.

Sky Coverage and Scan Strategy

• The maximum S/N for B modes is at l~5. To reliably measure l<10 (to really be sure we are seeing B modes) nearly full sky coverage is required.

• Depending on the degree to which the lensing and galactic foreground may be cleaned, smaller patches might yield a detection of gravity waves.

• The scan pattern used to modulate the signal and achieve sky coverage will be critical. Detailed mission simulations of different scan modes, coupled with realistic instrument models will be used to assess scan patterns and other experimental approaches.

• The decomposition of the polarization signal into E and B modes is sensitive to sky coverage and correlations between data points.

WMAP Scan Pattern as Example

Bennett et al. (2003) ApJ, 583, 1

Do We Need a Satellite?

Only in space can one achieve the stability and vantage needed to probe large angular scales (>1˚)…

This is the range where the telltale remnants of inflation are most likely to be found…

Therefore… yes!

Inflation Probe Concept Study - Summary

• Study period is two years.

• Starting in June 2004, study teams will participate a joint NASA/NSF/DOE task force to chart the next steps CMB polarization studies.

• The obstacles to detecting gravity waves are sensitivity, systematic errors, and astrophysical foregrounds. With a well designed mission, these obstacles can be surmounted. The goal of directly measuring the energy scale of inflation is within sight!

The 6 Phases of a Project

1. Enthusiasm! (Now)2. Disillusionment…3. Panic!!4. Search for the Guilty……5. Punishment of the Innocent!!!6. Praise and Honors for the Non-Participants

The End

Experimental Approach:Minimize Systematic Measurement Errors

• Differential design to minimize systematic errors• 5 microwave frequencies to understand foregrounds • 20 radiometers to allow multiple cross checks• Sensitivity to polarization• Accurate calibration (<0.5%)

calibration using modulation of the dipole from Earth’s velocity

• In-flight beam measurements on Jupiter• Minimize sidelobes & diffracted signals from Earth, Sun, Moon

L2 orbit• Multiple modulation periods to identify systematic effects• Minimize all observatory changes

L2 orbit; constant survey mode operations• Rapid and complex sky scan

observe 30% of the sky in an hour

SPIN-SYNCHRONOUS NON-SKY SIGNALS WERE THE LEADING CONCERN

SWITCH(0.4 msec)

SPIN(2 min)

PRECESS(1 hr)

ORBITAL(1 year)

Bennett et al. (2003) ApJ, 583, 1

Systematic Error Cross-Checks(Q1+Q2)/2

(W12-W34)/2(W12+W34)/2

(V1-V2)/2(V1+V2)/2

(Q1-Q2)/2

Hinshaw et al. (2003) ApJS, 148, 63

Temp x E-Polarization Power Spectrum

109r 20z

22080180

rt million years

uniformly suppress l>40 anisotropy by 30% (!)

Reionization

from z=1089scattering of CMB from electrons with non-random velocities

Kogut et al. (2003) ApJS, 148, 161Bennett et al. (2003) ApJS, 148, 1

http://lambda.gsfc.nasa.gov

Radial pattern around cold spotsTangential pattern around hot spots

Temperature quadrupole at z~1089 generates polarization

Temperature-Polarization Correlation

Jupiter Beam Maps

A-side B-side

Measured in flight Modeled

1. z=20 reionization: scattering of CMB from free electronsuniformly suppress l>40 anisotropy by 30% (!)Now detected:

2. z=1089 decoupling: scattering of CMB from electrons with non-random

velocitiespolarization correlates with temperature map1st detected by DASI, now have power spectrum

3. Gravity waves: Inflation-generated gravity waves polarize CMBneed new mission (e.g., NASA’s “Einstein Inflation Probe”

CMB Polarization

109r 20z

22080180

rt million years

Sky CoverageSky Coverage

Not to scale:Earth — L2 distance is 1% of Sun — Earth Distance

Earth

Sun

MAP at L2

1 Day

3 Months

6 Months - full sky coverage

129 sec. (0.464rpm) Spin

22.5° half-angle1 hour precession cone

A-side line of site

B-side line of site

MAP990159

Designed byM. Pospieszalskiat NRAO

Lay of the Land

B modes from lensing of E modes.

Reionization peak (z=20)

Recombination peak (z=1089)

E polarization from scalars and tensors

B polarization from tensors (gravity waves) only

Temperature (T) from scalar and tensor fluctuations

Gravity waves decay inside the horizon.

Current limit on tensors

• Universe began unimaginably hot and dense - billions of years ago

• Expanded and cooled

• Predictions:• A microwave afterglow light from the Big Bang

• Specific spectrum (intensity with wavelength)

• Many other predictions - all predictions since verified

1948: Big Bang Theory

1965: Discovery of Afterglow Light from Big Bang

Measurement ReceiverBell Telephone LabsNew Jersey

1978 Nobel Prizein Physics

RobertWilson

Arno PenziasFull sky image, green represents the afterglow

Beyond Einstein – Inflationary Universe

• One slide summary of inflation.