the implication of bicep2 : alternative interpretations on its results seokcheon lee (kias) @ snu...

The Implication of BICEP2: Alternative Interpretations on its

results

Seokcheon Lee (KIAS)@ SNU SeminarApr. 10th. 2014

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OUTLINE

• Cosmic Microwave Background Physics– Temperature Anisotropies– Polarization

• Implication of Background Imaging Cosmic Extragalac-

tic Polarization2– Data– Interpretation– Constraints on Inflation Models– Alternative Interpretations on its results

• Conclusions2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 )

CMB Spectra

2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 ) 3

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CMB Physics: Temperature Anisotropies

• The Universe was in thermal equilib-rium when the last scattering hap-pened

• We obtain the blackbody spectrum with average T = 2.725 K

• Last Scattering : when the photon is decoupled with electron2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 )

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• This is much colder than the H ionization energy (13.6 eV)

• After LS, the photon freely propagates to us (exception reionization)

• What we see is the fossil of the standing wave be-tween photon and baryon

• Deviation from Average T : Ensemble Average of this small deviation is called Temperature Power Spectrum

2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 )

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• Measure the anisotropy of T

• Measuring the directional difference of T (average doesn’t work)


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• General solution

Ωcr2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 )

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CMB Physics: T-E-B contaminations

• Temptation to measure 150-200 GHz


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Polarization: How to generate E & B-mode ?

• Generating E-mode (linear polariza-tion) – From both scalar and tensor perturba-

tions


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B-mode Polarization: How to generate B-mode ?

• Generating B-mode – From tensor perturbation (h)– From converting E-mode into B-mode

(Gravitational lensing, Birefringence, primordial magnetic field)


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B-mode Polarization : Why Important

• E & B modes around hot and cold spots

• Gravitational wave : Unique (?) channel to generate B-mode


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CMB Physics: Temperature and Polariza-

tion

N = ln[ ((10E16 GeV)/(10E-4 eV))] = 29 * ln[10] = 67


Limited by cosmic variance if only consider T : Knox & Turner (94) r < 0.1

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Implication of BICEP2: why BICEP2 ?

• Ground based telescope @ south pole / starting from Nov. 2005

• Frequencies : 100 (BICEP1), 150 GHz (BICEP2) / 26cm aperture

• Bolometer / 512 antenna (will be up-dated to 2560 antenna)

• Fig from BICEP


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Why BICEP ? II• Comparison for CMB polarization ex-

periments (G : ground, HEMT : High-Electron-

Mobility-Transistor, TES : Transition Edge Sensors)NAME BEGIN BASIS/LOC

Frequency Amplifier Targets

AMiBA 2002 G/Hawaii 86-102 Interfer-ometer

SZ, Pol

BICEP 2005 G/South Pole

100, 150 Bolome-ter

Large scale Pol

CBI (DASI) 2002-2008 (99-03)

G/Chille (SP)

26-36 HEMT Small scale

QUaD 2005-2007

G/ SP 100, 150 Bolome-ter

Small scale Pol

EBEX Future Ballon/Antarctica

150-450 Bolome-ter

Inflation GW

POLAR-BEAR

2011 G/Chille 150 Antenna-Coupled TES

Lensed B

Qubic Future G/ 97,150,230

Bolome-ter / TES

Interme-diate B

SPOrt Future Space Pol

SPT 2006 G/SP 90, 150, 220

Pol

SPIDER 2011 Balloon 90,150,220

Bolome-ter

Large scale Pol

Planck 2009 Space 30-857 HEMT/Bo-lometer


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Instrument : Optics


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Instrument


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Foreground Removal: Contaminations

• Contamination sources & Sensitivity


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Problems in Foreground Remove

• Not much is known about the polarization of fore-grounds

• Understanding and removing foregrounds are critical for Polarization detection

• Independent Component Analysis (ICA) used in T• None of studies take into account the impact of fore-

grounds in the presence of lensing and instrumental systematics

• Lack of a polarized dust map (BICEP relies on Planck data for this)– BICEP considered several models (FDS, BSS, LSA, PSM,

DDM1 p.12)– Important because this affects the result of r (Fig. 6 & 11)


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Results


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Results : continued


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Constraints on Inflation Models I

• Slow roll parame-ters

• Observable quanti-ties in terms of slow roll parame-ters to first order (Liddle & Lyth 00)


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Constraints on Inflation models

• Prefer simple inflation? Rule out many r < 10E-5 models?

• Not really, it can’t have large running index

• Does BICEP2 confirm large r if we trust their data? (assume their systematic is correct)


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Alternative Interpretations

• Many alternative ideas are possible (r = 0.1 still work)– Any other mechanism to create large

scale B-mode in addition to GW?– Lowering the scalar amplitude As

(Peloso et.al 1403.4596)– Primordial Magnetic field (Bonvin et.al

1403.6768)– Alleviate Bunch Davies vacuum (Collins

et.al 1403.4592)

• Cause the blue tilt nT > 1– Strongly against this, because it costs

changes in Temperature power spectrum (however it’s still consistent with error limit of T


FYI

2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 ) 24

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Conclusions

• BICEP2 shows the first B-mode signal (still need to investigate the origin of this signal)

• It might show that we are under the right track to understand the Universe

• For the data interpretation, we still need to understand many others– Need better control for foreground contamination– Need to suspect for alternative interpretations

and mechanism

• Stay tune for KECK and PLANCK


the implication of bicep2 : alternative interpretations on its results seokcheon lee (kias) @ snu...

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