Observing Cosmic Inflation with Precision Microwave Background Polarimetry by Dr H.Cynthia Chiang (University of KwaZulu-Natal)

1. Observing Cosmic Inflation
with
Precision Microwave
Background Polarimetry
H. Cynthia Chiang
University of KwaZulu-Natal
NITheP Associate Workshop
September 19, 2014

2. History of the universe
Big Bang
t = 0
End of inflation
t = 1e-35 sec
Dark matter decoupling
t = 1e-10 sec
EW symmetry breaking
t = 1e-12 sec
Electron-positron
annihilation
Neutrino
decoupling
t = 1 sec
Quark-hadron transition
t = 1e-5 sec
t = 5 sec BBN
t = 3 min
Matter-rad.
equality
t = 56 kyr
Formation of CMB
t = 400 kyr
Reionization
t = 0.2 gyr
Matter-lambda
equality
t = 9.5 gyr
You are here
t = 13.7 gyr
Image: Planck
Gravitational waves
Image: Monty Python

3. The need for inflation
The problems
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
The solution: inflation
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?)
The prediction
Quantum mechanical fluctuations perturb the metric
Scalar perturbations → density fluctuations // tensor perturbations → gravitational waves
FRW metric scalar perturbations vector perturbations tensor perturbations

4. Image: M. Hedman
Quadrupole moment in
incident radiation field Scattered radiation
is linearly polarised
Cold spot
Hot spot
Electron Observer's line
of 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!

5. “E” or “gradient” mode polarisation
has no handedness
“B” or “curl” mode polarisation has
handedness, i.e. rotation direction
Two flavors of polarisation
We can decompose a polarisation map...

6. The buzz about B modes
E modes are the CMB's “intrinsic 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.
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.

7. Gravitational waves of

8. Gravitational waves on (r = 1)

9. CMB polarisation power spectra
E-mode is mainly sourced by
density fluctuations and is the
intrinsic polarisation of the CMB
Degree-scale B-mode from
gravitational waves, amplitude
described by the tensor-to-scalar
ratio r.
Arcminute-scale B-mode from
weak gravitational lensing by
large-scale structure, partial
conversion of E-modes
Both flavors of B-mode
polarisation are much fainter than
E-mode, and they appear at
distinct angular scales.
E-mode
B-mode

10. 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

11. 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

12. What are we trying to learn now?
Large scale
EE and BB:
reionization
history
Medium/small
scale EE: fully
resolve peaks,
improve LCDM
parameter
constraints
Small scale BB:
lensing, neutrino
mass
Degree scale BB:
inflation physics

13. 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

14. The BICEP2 result
Scientific implications
 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
Should we believe it?
 Previous temperature data suggest r < 0.1
at 95% conf.
 Galactic contamination? Instrumental
systematics?
For a convincing result:
 Confirm electromagnetic spectrum is distinct
from foregrounds
 Confirm shape of angular power spectrum
 Signal must be statistically isotropic
B-mode power spectrum
temporal split jackknife
lensed-ΛCDM
r=0.2
5.3 sigma significance in
excess B-mode power

15. 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

16. Antarctic long-duration ballooning
Balloon launch pad, McMurdo station, Antarctica
SPIDER test
integration in
Texas, USA
 Launch from McMurdo station, Flight track
circumnavigate continent in ~2
weeks
 Float altitude: 40 km
Volume: 1 million m3
Max payload weight: 3600 kg
 More info: BLAST the movie,
EBEX launch on youtube

17. SPIDER == “6x BICEP2
telescopes” bundled together
Figures: J. Gudmundsson

19. SPIDER's six telescopes

20. Focal plane: antenna-coupled TES bolometers
8mm
Each spatial pixel:
Two orthogonal antenna arrays
16 x 16 dipole slot antennas
Each focal plane: 4 tiles x 64 pixels x 2 polarizations = 512 detectors
Detectors: Al / Ti TES bolometers

21. 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!
Temperature
353 GHz
Synchrotron
90 GHz
Dust
150 GHz

22. Large scale
EE and BB:
reionization
history
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

23. What will Spider do for you?
B modes for
r = 0.2
and
r = 0.03
Dust 150 GHz
Synchrotron
90 GHz
 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.

24. SPIDER status: counting down to a December flight
Insert assembly LDB cryostat on
Preparing for
cooldown
Team SPIDER owns
the machine shop!
the gondola

25. McMurdo 2014!

26. 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