Physics of CMB Polarization
and Its Measurement
HEP seminar at Kyoto University
April 13th, 2007

Akito KUSAKA
University of Tokyo

Outline Physics of CMB and its Polarization› What does WMAP shed light on?
› Unsolved Problems: Beyond SM› CMB Polarization as a Probe for Inflation
 Measurement of CMB Polarization› Detection Techniques› Experimental Status and Prospects
x Current Measurements (1st generation)
x 2nd Generation Experiments, and beyondPhysics of CMB and Its Polarization

Cosmology After WMAP
NASA/WMAP Science TeamWMAP (+ Others) Flat ΛCDM› Ωall ~ 1› ΩΛ = 0.74 ± 0.06
› Ωmh2 = 0.13 ± 0.01

(Ωm ~ 0.26)› Ωbh2 = 0.022 ± 0.001
 +Implications› Dark Energy ~ Λ› Consistent w/ Inflation

Solved and Unsolved Problems
Solved: Time Evolution of the Universe

NASA/WMAP Science Team

Unsolved: Physics of the Beginning (Inflation)
Source of the Evolution (Dark Energy, Dark Matter)

Unsolved Problems
 Inflation› Is it true?
› What’s the correct model?
› Shape of potential: Physics at GUT Scale?
› Signature: Primordial Gravitational-Wave (CGB?)› Detectable via CMB Polarization
 Dark Energy› Equation of State: w = p/ρ
› Dark Energy = Cosmological Constant?
(i.e., w = −1 ?)Cluster Survey, Weak Lensing,
CMB SZE, ABO, SNe Ia, etc...

Digression:
Can we go further with CMB?
 Cosmic VarianceThree-Year WMAP, Hinshaw et al.

› We want to measure
the “PDF” of CMB.
› We only have one
realization (our sky),i.e., one event.
› TT at small l (incl. firstpeak) is now cosmicvariance limited.
 To go further:› TT at large l› Polarization

TT (Temperature) Correlation
Black: WMAP Three-Year
Green: WMAP First-Year
Gray Band: Cosmic Variance Expectation

CMB Polarization
 CMB is from last(Thomson) scatteringÆLinearly polarized Anisotropy

ÆNon-zero overall
polarization

A CMB Polarization Primer (Hu & White)E-mode and B-mode
 Polarization: Tensor-field› Tensor = “Bar” without
direction› c.f. Vector = “Bar” withdirection

E-modeB-mode+E+B−E−B

 Decomposable into E-mode and B-mode› Analogous to the vector
field decomposition to(rot. free mode) + (div.
free mode)B-mode Polarization
TT is around here (~103μK)

 Only sourced bygravitational wave
from Inflation

CMB Task Force› Unique signal ofInflation› Intensity of B-mode ÆTensor/Scalar ∝ V› V: Inflation potential,GUT scale ?
 Gravitational lensing

converts E-mode ÆB-mode at large l.

r = (T/S)2
T/S~0.1 if V~GUT scale

More on CMB Polarization
 Lensing B-mode› Not only contamination for primordial B-mode› Can be a probe for mass distribution Æ
information for Dark Energy w

 E-mode and TE-correlation› Improvement in cosmological parameters› Consistency check (robustness w.r.t.

assumptions such as adiabaticity) TB- and EB-correlation› Zero (otherwise, there is parity violation)

Measurement of CMB Polarization

Primary Target: B-mode
Two possible targets
 Small l (l~5: ~50°)

CMB Task Force› Free from lensing B› Originates fromreionization› Advantageous toSatellite
 Large l (l~100: ~2°)
› Could be lensing B
dominant (subtract?)l~5l~100› Ground based iscompetitive
NOTE: atmosphere is not polarizedBasics of Polarization
 Stokes parameters (I, Q, U, V)› A set of parameters fully characterizing
intensity and polarization of radio wave.
› I: Intensity (Æ T in CMB)
› Q, U: Two linear polarization (Æ E, B in CMB)
› V: Circular polarization (zero in CMB)−Q
2
2
U = 2ExEy −U
Q = Ex − Ey+Q+U

ectortDe Two technologies: Bolometer vs. HEMT Feasibility Array Choice of band

› Which region of 20GHz~500GHz› “Foreground” contribution

HEMT (+ diode detector)
 “Usual” way of radiowave detection:amp. Æ rectification
 Establishedtechnology› WMAP, DASI,CAPMAP, …
 Limited by quantum

noise: Tdet ∝ hν/k
› Good in low ν(ν<100GHz)

WMAP receiver
HEMT Amp.

Diode detector

HEMT (+ diode detector)
Pseudo-correlation polarimeter (Pseudo-)Correlation

polarimeter Gain diff. cancellation
 Recent technology
breakthrough(MMIC+packaging)for arraying
CAPMAP polarimeter~30cm

QUIET polarimeter(90GHz)~3cm(from CMB task force)Bolometer Direct detection of total“power” of radio wave
 No quantum noise limit Technically challenging
 Low ν Æ large heat load
Æ Difficulty in low ν› Overcome by antenna

coupled bolometer Promising detector typein futureBerkeley Bolometer

Bolometer

TES Bolometer
Antenna Web Good at making

large array Antenna coupledbolometer has
polarization sensitivity|Ex|2, |Ey|2 measurement(PSB)
Berkeley PSB

Bolometer(from CMB task force)~12 cm
Dipole Antenna

SPT Bolometer Array

“Foreground”
 Contamination for“Background”
measurement:“Foreground”
 Primary, inevitablesystematic error Two large sources

PLANCK “Blue Book”› Synchrotron radiationfrom cosmic ray› Dust emission (dustaligned in B field)

Spectra of CMB and foreground sources

Choice of Technology
 HEMT› Quantum noise limit:
Tdet ~ hν/kB› Good at ν<100GHz› Relatively established› MMIC + packaging
technology for array› (Pseudo-)correlation
polarimeter Bolometer› No quantum noise limit› Good at ν>100GHz› Also good atν<100GHz withantenna coupling› Challenging› Suitable for array› “Brute force”
polarimeter› (Correlator type is alsopossible)

Multi-pole analysis
 TT correlation (scalarfield)› Spherical harmonics
expansion Polarization (tensorfield)› Tensor sphericalharmonics expansion› Simple FT of div. androt. field (for smallpatch of the sky) Practical difficulty› Irregular sampling› Border of patch

Three-Year WMAP, Hinshaw et al.

Current Status
 Significantly non-zero

EE Correlation

EE correlation is found› WMAP, DASI, CBI,BOOMERanG,
CAPMAP WMAP TE correlation› Improvement of limits
on cosmologicalparameters No significant BB

measurement, yet

Three-Year WMAP, Page et al.

Coming Experiments
 Targets› Primordial B from inflation› Lensing B for mass profile measurement(experiments w/ high resolution)› E to improve limits on cosmologicalparameters Detector improvement› Large array Æ Better statistics› Better detector sensitivity

Coming Experiments
 BolometerBalloon
Taking data(Main target=SZE)› (AMiBA), BICEP, BRAIN/ClOVER, EBEX, MBI-B,MAXIPOL, PAPPA, PolarBeaR, Polatron(?),
QUaD, (SPT), Spider HEMT› BaR-SPOrt(?)/SPOrt(?), QUIET Bolometer + HEMT (depending on freq.)› PLANCK
See the following site for compilation
http://lambda.gsfc.nasa.gov/links/experimental_sites.cfm

QUIET Q/U Imaging ExperimenT Detector: HEMT››››Two bands: W-band (90GHz) and Q-band (40GHz)
HEMT array (91 elements for W, 19 elements for Q)
The only next generation HEMT experiment
The only next generation (B competitive) program
straddling across 60GHz
x NOTE: 60GHz = WMAP implies lowest foreground Site: Chile, Atacama Collaboration› ~10 US institutes (incl. CAPMAP&CBI) + Oxford, MPI Bonn
› ~20 staff + students
 Cost: ~a few M USD

QUIETAll the figures from QUIET web site
http://quiet.uchicago.edu/

CBI site at Chile

Sensitivity

Deployment: 2007 Fall, First Science Result: 2008 Summer

Next Next Generation
 Ultimate CMBexperiment› Satellite› Target: B-mode
at low l› Bolometer (Ground Based) Japanesecommunity may
take part› Tohoku› KEK› …

Beyond Einstein Program
http://universe.nasa.gov/program.html

Summary Unsolved Problems of Cosmology› Inflation and Dark Energy
 B-mode Polarization of CMB› Sensitive to Inflation
 Detector Technology› Bolometer vs. HEMT Current Measurement: E-mode found Experiments Dedicated to B-mode:

coming soon…