BICEP2 Results, Implications, and the Future of Tensor Cosmology

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BICEP2 Results, Implications,

and the Future of Tensor Cosmology

Chao-Lin Kuo

Stanford University

SLAC National Accelerator Laboratory

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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..

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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.) “

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t Now

t

Need something to move the blue lines below the red line

Inflation

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How does Inflation work?

• Solved the horizon and flatness problems

• How is it achieved ? Exponential expansion.

Slow roll, ~ const. Hubble

~ exponential expansion (inflation)

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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

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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

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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

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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

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E E

B B

Only gravitational waves can generate B-modes

Seljak & Zaldarriaga ‘97

Kamionkowski, Kosowsky, Stebbins ‘97

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Gravitational waves generate

E-mode polarization

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Gravitational waves generate B-mode polarization

!!!

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The polarization pattern is unique, but small

Vertical / Horizontal differ by

1 part in 30,000,000

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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..

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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

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John Q Public for the Bicep2 Collaboration

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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

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BICEP1: 2006, 2007, 2008 BICEP2: 2010, 2011, 2012

Keck Array: 2011, 2012, 2013, … BICEP3: 2015…

A very focused program on B-modes

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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 ..

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A very focused program on B-modes

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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

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3 BICEP2 year = 30 BICEP1 years!

BICEP1 48 150 GHz detectors

BICEP2 512 150 GHz detectors

JPL : antenna-coupled TES arrays

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0.1 mm

Radiation

Converted to heat Superconducting

thermometer

CMB light from antenna BICEP2 Detector: Transition-Edge Superconductor

Detecting the CMB radiation

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JPL

>100 tiles

(>12,000 detectors)

have been produced

over the past 8 yrs

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Scale:

Total polarization (3 yrs of data)

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B-mode contribution

Scale:

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B-mode contribution

Scale:

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Scale:

B-mode contribution

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Scale:

B-mode contribution

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The Bicep2 Collaboration

Temperature and Polarization Spectra

power spectra

temporal split jackknife

lensed-ΛCDM r=0.2

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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

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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.

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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

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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 (n_T=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:

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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.

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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 A_L= 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 A_L we find:

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Compatibility with Indirect Limits on r

SPT+WMAP+BAO+H₀

Planck+SPT+ACT+WMAP_pol

: 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)

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BICEP2 and upper limits from other experiments:

Polarbear SPT x-corr

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(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

• …..

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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

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BICEP1: 2006, 2007, 2008 BICEP2: 2010, 2011, 2012

Keck Array: 2011, 2012, 2013, 2014 (576 100GHz detectors)…

BICEP3: 2015 –

(another 2560 100GHz detectors)

Prospects

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Advanced materials (99.6% Al ₂ O ₃ )

For large BICEP3 cold optics

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Epoxy-based AR-coating

On curved lens

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Strain-relieving AR layer

using high power UV laser

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Large aperture

Metal mesh IR blocking filters

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49 After B2? Increasing the sky coverage

Declination

limit at the

South Pole

BICEP2

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50 After B2? Increasing the sky coverage

Declination limit at the South Pole

BICEP3/Keck

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51 After B3? Increasing the sky coverage

Declination limit at the South Pole BICEP2

T-REX

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52 T-REX (TensoR EXperiment):

Straight duplication of BICEP3

A project that is “shovel-ready”

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Where will T-REX land?

BICEP2

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Where will T-REX land?

BICEP2

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Keith Vanderlinde

Thank you !

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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

2010

2011

2012

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Spectral Index of the B-mode Signal

Comparison of B2 auto with B2

₁₅₀

x B1

₁₀₀

constrains 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

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Spectral Index of the E-mode Signal

Comparison of B2 auto with B2

₁₅₀

x B1

₁₀₀

constrains 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

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Calibration Measurements

Detector Polarization Calibration

Hi-Fi beam maps of individual detectors Far field beam mapping

Detailed description in

companion Instrument Paper

For instance...

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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!

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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.

BICEP2 Results, Implications, and the Future of Tensor Cosmology