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