BICEP2 Results, Implications,
and the Future of Tensor Cosmology
Chao-Lin Kuo
Stanford University
SLAC National Accelerator Laboratory
Amazing combination of
Theoretical ideas :
•Inflation
•Inflation generates gravitational waves
•Gravitational waves generate B-modes
Technology :
• Refractor in a cryostat
• Polarimeters on a chip
• TES and SQUIDs
•and focus, hard work , faith, etc..
Next few slides are placeholders for Chao Lin’s slides on
“ what is inflation, why do we believe it, GWs as smoking gun,
how GW's make the B-mode pattern, it is very faint! (1/20,000,000, i.e.
for every 20,000,000 photons oriented like his, on average you may get
20,000,001 oriented the other.) “
t Now
t
t
Need something to move the blue lines below the red line
Inflation
How does Inflation work?
• Solved the horizon and flatness problems
• How is it achieved ? Exponential expansion.
Slow roll, ~ const. Hubble
~ exponential expansion (inflation)
Generation of perturbations
• This is the part that connects quantum w/ cosmos
• Prior to BICEP2, the properties of the scalar
perturbations have become the strongest evidence for inflation
– Adiabatic (1 D.o.F. , related to inflaton field φ) – Gaussian (vacuum state of φ)
– Spectral index n s <~ 1
Sub-atomic
vacuum fluctuations of “inflaton”
Sub-atomic
vacuum fluctuations
of graviton (quanta of gravity)
Inflation Gravitational waves detected by BICEP2
Density perturbations studied by Planck, WMAP, SPT, etc.
Density perturbations and
gravitational waves
Generation of scalar/tensor perturbations
Quantum fluctuations in the vacuum state of the
inflaton/graviton fixes the r.m.s of the linear solutions
Time t
Horizon exit
Grishchuk 74; Starobinsky 79
Rubakov et al, 82; Frabri & Pollock , 82 Mukhanov & Chibisov ‘81
Guth& Pi; Hawking; ‘82; Bardeen et al., ’83; Sasaki ‘83
→ two linear wave equations
for scalar /tensor
Inflationary B-modes, known as the
“Holy Grail” of cosmology
• Started out as graviton vacuum fluctuations
• Energy scale of inflation ~ expansion rate ~ GW amplitude
• Alternative models generate no GW
• Field range and “UV” completeness
E E
B B
Only gravitational waves can generate B-modes
Seljak & Zaldarriaga ‘97
Kamionkowski, Kosowsky, Stebbins ‘97
Gravitational waves generate
E-mode polarization
Gravitational waves generate B-mode polarization
!!!
The polarization pattern is unique, but small
Vertical / Horizontal differ by
1 part in 30,000,000
Amazing combination of
Theoretical ideas :
•Inflation
•Inflation generates gravitational waves
•Gravitational waves generate B-modes
Technology :
• Refractor in a cryostat
• Polarimeters on a chip
• TES and SQUIDs
•and focus, hard work , faith, etc..
South Pole is the Mecca of CMB research (BICEP1, BICEP2, Keck Array, BICEP3)
•High, dry, cold, low water vapor in the atmosphere
•Stable climate for continuous 6 months
•Great logistical support (US NSF-Office of Polar Program)
SPT
ACBAR
BICEP3
John Q Public for the Bicep2 Collaboration
BICEP/Keck series BICEP1/2/3
Keck Array
microwave (95/150 GHz) Superconducting sensors Low temperature physics (0.25K)
Lithographic detectors High packing density Mass production
1
BICEP1: 2006, 2007, 2008 BICEP2: 2010, 2011, 2012
Keck Array: 2011, 2012, 2013, … BICEP3: 2015…
A very focused program on B-modes
BICEP1: 2006, 2007, 2008 BICEP2: 2010, 2011, 2012
Keck Array: 2011, 2012, 2013, … BICEP3: 2015…
A very focused program on B-modes
More and more detectors ..
A very focused program on B-modes
BICEP1: 2006, 2007, 2008 (r<0.70; 95%) BICEP2: 2010, 2011, 2012
Keck Array: 2011, 2012, 2013, … BICEP3: 2015…
A very focused program on B-modes
3 BICEP2 year = 30 BICEP1 years!
BICEP1 48 150 GHz detectors
BICEP2 512 150 GHz detectors
JPL : antenna-coupled TES arrays
0.1 mm
Radiation
Converted to heat Superconducting
thermometer
CMB light from antenna BICEP2 Detector: Transition-Edge Superconductor
Detecting the CMB radiation
JPL
>100 tiles
(>12,000 detectors)
have been produced
over the past 8 yrs
Scale:
Total polarization (3 yrs of data)
B-mode contribution
Scale:
John Q Public for the Bicep2 Collaboration
B-mode contribution
Scale:
Scale:
B-mode contribution
Scale:
B-mode contribution
The Bicep2 Collaboration
Temperature and Polarization Spectra
power spectra
temporal split jackknife
lensed-ΛCDM r=0.2
The Bicep2 Collaboration
Bandpower Deviations
Bandpower deviations from mean of lensed-
ΛCDM+noise simulations and normalized by the std of those sims
real data
lensed-ΛCDM + noise sims
± 1σ
± 2σ
The Bicep2 Collaboration
Check Systematics: Jackknifes
Splits the 4 boresight rotations
Splits by time
Splits by channel selection
Splits by possible external contamination
Splits to check intrinsic detector properties
Amplifies differential pointing in comparison to fully added data. Important check of
deprojection. See later slides.
Checks for contamination on long (“Tag Split”) and short (“Scan Dir”) timescales. Short timescales probe detector transfer functions.
Checks for contamination in channel subgroups, divided by focal plane location, tile location, and readout electronics grouping
Checks for contamination from ground-fixed signals, such as polarized sky or magnetic fields, or the moon
Checks for contamination from detectors with
best/worst differential pointing. “Tile/dk” divides the data by the orientation of the detector on the sky.
The Bicep2 Collaboration
Additional Cross Spectra
BICEP2 auto spectrum compatible with B2xB1c cross spectrum
~3σ evidence of excess power in the cross spectrum
Additionally form cross spectrum with 2 years of data from Keck Array, the successor to BICEP2
Excess power is also evident in the B2xKeck cross spectrum
Form cross spectrum between BICEP2 and BICEP1 combined (100 + 150 GHz):
Cross spectra:
Powerful additional evidence against a systematic origin of the apparent signal
The Bicep2 Collaboration
Constraint on Tensor-to-scalar Ratio r
Substantial excess power in the region where the
inflationary gravitational wave signal is expected to peak Find the most likely value of the tensor-to-scalar ratio r
Apply “direct likelihood” method, uses:
→ lensed-ΛCDM + noise simulations
→ weighted version of the 5 bandpowers
→ B-mode sims scaled to various levels of r (nT=0)
Uncertainties here include sample variance at r=0.2
best fit
r = 0.2 with uncertainties dominated by sample variance
PTE of fit to data: 0.9
→ model is perfectly acceptable fit to the data r=0 ruled out at 7.0
σ
Within this simplistic model we find:
The Bicep2 Collaboration
Polarized Dust Foreground Projections
FDS Model
Dashed: Dust auto spectra
Solid: BICEP2xDust cross spectra
The BICEP2 region is chosen to have extremely low foreground emission.
Use various models of polarized dust emission to estimate
foregrounds.
All dust auto spectra well below observed signal level.
Cross spectra consistent with zero.
The Bicep2 Collaboration
Joint Constraint on r and Lensing Scale Factor
Contours: 1&2σ intervals from BICEP2 data
Planck’s 1σ band on AL
Lensing deflects CMB photons, slightly mixing the dominant E-modes into B-modes --
dominant at high multipoles
Planck data constrain the amplitude of the lensing effect to AL= 0.99 ± 0.05.
BICEP2 data is perfectly compatible with a lensing amplitude of A= 1.
Marginalizing over r, we detect lensing B- modes at 2.7
σ
In the joint constraint on r and AL we find:
The Bicep2 Collaboration
Compatibility with Indirect Limits on r
SPT+WMAP+BAO+H0
Planck+SPT+ACT+WMAPpol
: r < 0.11 : r < 0.11 Using temperature data over a wide range of angular scales limits on r have been set:
r=0.2 makes a small change to the temperature spectrum.
(In this plot r=0.2 simply added to Planck best fit model with no re-optimization of other parameters)
The Bicep2 Collaboration
BICEP2 and upper limits from other experiments:
Polarbear SPT x-corr
(Standard) implications
• Inflation happened
• Gravity is quantized
• Inflation happened at the GUT scale
• Chaotic Inflation models are favored
• Many string-motivated models have been ruled out
• Inflation field moves over Super Planckian range → needs shift symmetry in Q.G.
• Half of axion parameter space is ruled out
• Low ell anomaly becomes worse
• …..
BICEP1: 2006, 2007, 2008 (r<0.70; 95%)
BICEP2: 2010, 2011, 2012 (r=0.2 +0.07-0.05) Keck Array: 2011, 2012, 2013,
2014 (576 100GHz detectors)…
BICEP3: 2015…
Prospects
BICEP1: 2006, 2007, 2008 BICEP2: 2010, 2011, 2012
Keck Array: 2011, 2012, 2013, 2014 (576 100GHz detectors)…
BICEP3: 2015 –
(another 2560 100GHz detectors)
Prospects
Advanced materials (99.6% Al 2 O 3 )
For large BICEP3 cold optics
Epoxy-based AR-coating
On curved lens
Strain-relieving AR layer
using high power UV laser
Large aperture
Metal mesh IR blocking filters
49
After B2? Increasing the sky coverage
Declination
limit at the
South Pole
BICEP2
50
After B2? Increasing the sky coverage
Declination limit at the South Pole
BICEP3/Keck
51
After B3? Increasing the sky coverage
Declination limit at the South Pole BICEP2
T-REX
52
T-REX (TensoR EXperiment):
Straight duplication of BICEP3
A project that is “shovel-ready”
Where will T-REX land?
BICEP2
Where will T-REX land?
BICEP2
Keith Vanderlinde
Thank you !
BICEP2 Postdocs
Colin Bischoff
Immanuel Buder
Jeff Filippini
Stefan Fliescher
Martin Lueker
Roger O’Brient
Walt Ogburn
Angiola Orlando Zak Staniszewski Abigail Vieregg
Randol Aikin Justus Brevik
Kirit Karkare Jon Kaufman
Sarah Kernasovskiy
Chris Sheehy Grant Teply
Jamie Tolan
Chin Lin Wong
BICEP2 Graduate Students
BICEP2
Winterovers
Steffen Richter
Steffen Richter
Steffen Richter
2010
2011
2012
John Q Public for the Bicep2 Collaboration
Spectral Index of the B-mode Signal
Comparison of B2 auto with B2
150x B1
100constrains signal frequency dependence, independent of foreground projections If dust, expect little cross-correlation
If synchrotron, expect cross higher than auto
Likelihood ratio test: consistent
with CMB spectrum, disfavor
pure dust/sync at 2.2/2.3 σ
John Q Public for the Bicep2 Collaboration
Spectral Index of the E-mode Signal
Comparison of B2 auto with B2
150x B1
100constrains signal frequency dependence, independent of foreground projections If dust, expect little cross-correlation
If synchrotron, expect cross higher than auto
Likelihood ratio test: consistent
with CMB spectrum, disfavor
pure dust/sync at 11/30 σ
John Q Public for the Bicep2 Collaboration
Calibration Measurements
Detector Polarization Calibration
Hi-Fi beam maps of individual detectors Far field beam mapping
Detailed description in
companion Instrument Paper
For instance...
John Q Public for the Bicep2 Collaboration
Systematics beyond Beam imperfections
All systematic effects that we could imagine were investigated!
We find with high confidence that
the apparent signal cannot be
explained by instrumental
systematics!
John Q Public for the Bicep2 Collaboration
Constraint on r under Foreground Projections
Adjust likelihood curve by subtracting the dust projection auto and cross spectra from our bandpowers:
Probability that each of these models reflect reality hard to assess
DDM2 uses all publicly available information from Planck - modifies constraint to:
r=0 still ruled out at 5.9
σ
Dust contribution is largest in the first bandpower.
Deweighting this bin would lead to less deviation from our base result.