Observing Cosmic Inflationwith

Precision MicrowaveBackground Polarimetry

H. Cynthia ChiangUniversity of KwaZulu-Natal

NITheP Associate WorkshopSeptember 19, 2014

Big Bangt = 0

End of inflationt = 1e-35 sec

EW symmetry breakingt = 1e-12 sec

Dark matter decouplingt = 1e-10 sec

Quark-hadron transitiont = 1e-5 sec

Neutrinodecoupling

t = 1 sec

Electron-positronannihilation

t = 5 secBBNt = 3 min

Matter-rad.equality

t = 56 kyr

Formation of CMBt = 400 kyr

Reionizationt = 0.2 gyr

Matter-lambdaequalityt = 9.5 gyr

You are heret = 13.7 gyr

Image: Planck

Gravitational waves

Image: Monty Python

History of the universe

The need for inflation

The problems

Accelerated expansion at GUT energy scales solves all the above problems!“Easy” to implement inflation with a scalar field(The fine print: what is this scalar field?)

Quantum mechanical fluctuations perturb the metricScalar perturbations → density fluctuations // tensor perturbations → gravitational waves

Why is the universe so uniform? And why don't we see any monopoles?Why is the universe so flat / old?

Deviations from flatness grow with time

FRW metric scalar perturbations vector perturbations tensor perturbations

The solution: inflation

The prediction

Image: M. Hedman

Quadrupole moment inincident radiation field

Scattered radiationis linearly polarised

Cold spot

Hot spotElectron

Observer's lineof sight

Polarisation in the CMB

CMB is intrisically polarised because of temperature anisotropies

Mechanism: Thomson scattering within local quadrupole moments

Polarised signal is small: ~100x weaker than temperature anisotropies!

“E” or “gradient” mode polarisationhas no handedness

“B” or “curl” mode polarisation hashandedness, i.e. rotation direction

We can decompose a polarisation map...

Two flavors of polarisation

We expect them to be there because of scattering processes in the CMB Temperature anisotropies predict E-mode spectra with almost no extra information Not only that, but “standard” CMB scattering physics generates ONLY E modes.

E modes are the CMB's “intrinsic polarisation”

So then where do B modes come from?

Inflation: exponential expansion of universe (x 1025) at 10-35 sec after big bang. “Smoking gun” signature = gravitational wave background that leaves a B-mode imprint on CMB polarization!

Gravitational lensing by large scale structure converts some of the E-mode polarisation to B-mode. Use this to study structure formation, “weigh” neutrinos.

How can we tell the difference between the above two? Degree vs. arcminute angular scales.

The moral of the story: B modes tell us things about the universe that temperature and E modes can't.

The buzz about B modes

Gravitational waves of

Gravitational waves on (r = 1)

CMB polarisation power spectra

Arcminute-scale B-mode from weak gravitational lensing by large-scale structure, partial conversion of E-modes

Degree-scale B-mode from gravitational waves, amplitude described by the tensor-to-scalar ratio r.

Both flavors of B-mode polarisation are much fainter than E-mode, and they appear at distinct angular scales.

E-mode is mainly sourced by density fluctuations and is the intrinsic polarisation of the CMB

E-mode

B-mode

Current CMB polarisation measurements

E-mode polarisation measured with high precision: acoustic peaks have been detected and are consistent with LCDM

NEWS FLASH: the first detections of B-mode polarisation were reported just in the past year!

Inflationary: BICEP2 detected r = 0.2

Lensing:Detections by SPT and Polarbear, consistent with theoretical expectations

Current CMB polarisation measurements

E-mode polarisation measured with high precision: acoustic peaks have been detected and are consistent with LCDM

NEWS FLASH: the first detections of B-mode polarisation were reported just in the past year!

Inflationary: BICEP2 detected r = 0.2

Lensing:Detections by SPT and Polarbear, consistent with theoretical expectations

What are we trying to learn now?

Large scaleEE and BB:reionizationhistory

Medium/small scale EE: fully resolve peaks, improve LCDM parameter constraints

Small scale BB:lensing, neutrino mass

Degree scale BB:inflation physics

Diferent instruments for diferent angular scales

EBEX

PIPER

QUBIC

QUIJOTE

Planck

ACTPol SPTpol

ABS BICEP2/Keck

GroundBIRD

Polarbear

SPIDER

CLASS

POLAR-1

Large angular scales Medium angular scales Small angular scales

The BICEP2 result

Measured r is directly related to potential energy of field driving inflation:r = 0.2 implies 2 x 1016 GeV

Field driving inflation is moved by ~5x Planck mass, which is a challenge for model building

Scientific implications

Previous temperature data suggest r < 0.1 at 95% conf.

Galactic contamination? Instrumental systematics?

Should we believe it?

Confirm electromagnetic spectrum is distinct from foregrounds

Confirm shape of angular power spectrum

Signal must be statistically isotropic

For a convincing result:

B-mode power spectrumtemporal split jackknifelensed-ΛCDM r=0.2

5.3 sigma significance in excess B-mode power

SPIDER: a new instrument for CMB polarimetry

SPIDER science goals

Measure inflationary B modes with sensitivity of r < 0.03 at 3

Characterize polarized foregrounds

Instrumental approach

Need high sensitivity, fidelity

Long duration balloon platform (2 flights, 20+ days each)

0.5 deg resolution over 8% of the sky, target 10 < ell < 300

6 compact, monochromatic refractors in LHe cryostat

2600 detectors split between 90,150, 280 GHz

Polarization modulation: HWPs

Balloon launch pad, McMurdo station, Antarctica

SPIDER test integration in Texas, USA

Flight track Launch from McMurdo station, circumnavigate continent in ~2 weeks

Float altitude: 40 kmVolume: 1 million m3

Max payload weight: 3600 kg More info: BLAST the movie,

EBEX launch on youtube

Antarctic long-duration ballooning

SPIDER == “6x BICEP2 telescopes” bundled together

Figures: J. Gudmundsson

SPIDER's six telescopes

Focal plane: antenna-coupled TES bolometers

8mm

Each spatial pixel:Two orthogonal antenna arrays16 x 16 dipole slot antennas

Detectors: Al / Ti TES bolometers

Each focal plane: 4 tiles x 64 pixels x 2 polarizations = 512 detectors

SPIDER flight plan

SPIDER will map 8% of the sky in an exceptionally clean region (encompasses the “southern hole”)

First flight: 90 GHz and 150 GHz to maximize sensitivity for a B-mode detection

Second flight: expand frequency coverage to further characterize the signal

First flight: December 2014!

Temperature353 GHz

Synchrotron90 GHz

Dust150 GHz

Large scaleEE and BB:reionizationhistory

Medium/small scale EE: fully resolve peaks, improve LCDM parameter constraints

Small scale BB:lensing, neutrino mass

Degree scale BB:inflation physics

What will Spider do for you?

Spider's ell range

What will Spider do for you?

SPIDER has enough sensitivity to constrain r < 0.03 at 3 (even with foregrounds).

With high sensitivity, multiple frequencies, and extended sky/ell coverage, SPIDER will greatly improve our ability to distinguish primordial B modes and Galactic foregrounds.

If r = 0.2, we still have sensitivity to spare to restrict our analysis to a clean patch of sky.

Dust 150 GHz

Synchrotron90 GHz

B modes forr = 0.2and

r = 0.03

SPIDER status: counting down to a December flight

Preparing for cooldown

Team SPIDER owns the machine shop!

Insert assembly LDB cryostat on the gondola

McMurdo 2014!

The trouble with foregrounds

30 GHz 44 GHz 70 GHz

100 GHz 143 GHz 217 GHz

343 GHz 545 GHz 857 GHz

“It's like more than just bugs on a windshield that we want to remove to see the light, but a storm of bugs all around us in every direction.” – Charles Lawrence re: foreground removal