1. The Implication of BICEP2 : Alternative Interpretations on its results Seokcheon Lee (KIAS) @ SNU Seminar Apr. 10 th. 2014

2. OUTLINE Cosmic Microwave Background Physics –Temperature Anisotropies –Polarization Implication of B ackground I maging C osmic E xtragalactic P olarization 2 –Data –Interpretation –Constraints on Inflation Models –Alternative Interpretations on its results Conclusions 2014-04-102 SNU SEMINAR ( 이석천 / 고등과학원 )

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

4. CMB Physics : Temperature Anisotropies The Universe was in thermal equilibrium when the last scattering happened We obtain the blackbody spectrum with average T = 2.725 K Last Scattering : when the photon is decoupled with electron 2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 ) 4

5. CMB Physics : Temperature Anisotropies 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 between 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 ) 5

6. CMB Physics : Temperature Anisotropies Measure the anisotropy of T Measuring the directional difference of T (average doesn’t work) 2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 ) 6

7. CMB Physics : Temperature Anisotropies General solution Ω cr 2014-04-107 SNU SEMINAR ( 이석천 / 고등과학원 )

8. CMB Physics : T-E-B contaminations Temptation to measure 150-200 GHz 2014-04-10 SNU SEMINAR ( 이석천 / 고등과학원 ) 8

9. Polarization : How to generate E & B-mode ? Generating E-mode (linear polarization) –From both scalar and tensor perturbations 2014-04-109 SNU SEMINAR ( 이석천 / 고등과학원 )

10. 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) 2014-04-1010 SNU SEMINAR ( 이석천 / 고등과학원 )

11. B-mode Polarization : Why Important E & B modes around hot and cold spots Gravitational wave : Unique (?) channel to generate B-mode 2014-04-1011 SNU SEMINAR ( 이석천 / 고등과학원 )

12. CMB Physics : Temperature and Polarization N = ln[ ((10E16 GeV)/(10E-4 eV))] = 29 * ln[10] = 67 2014-04-1012 SNU SEMINAR ( 이석천 / 고등과학원 ) Limited by cosmic variance if only consider T : Knox & Turner (94) r < 0.1

13. 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 updated to 2560 antenna) Fig from BICEP 2014-04-1013 SNU SEMINAR ( 이석천 / 고등과학원 )

14. Why BICEP ? II Comparison for CMB polarization experiments (G : ground, HEMT : High-Electron- Mobility-Transistor, TES : Transition Edge Sensors ) NAMEBEGINBASIS/LO C FrequencyAmplifierTargets AMiBA2002G/Hawaii86-102Interferome ter SZ, Pol BICEP2005G/South Pole 100, 150BolometerLarge scale Pol CBI (DASI)2002-2008 (99-03) G/Chille (SP) 26-36HEMTSmall scale QUaD2005-2007G/ SP100, 150BolometerSmall scale Pol EBEXFutureBallon/Anta rctica 150-450BolometerInflation GW POLARBE AR 2011G/Chille150Antenna- Coupled TES Lensed B QubicFutureG/97,150,230Bolometer / TES Intermediat e B SPOrtFutureSpacePol SPT2006G/SP90, 150, 220 Pol SPIDER2011Balloon90,150,220BolometerLarge scale Pol Planck2009Space30-857HEMT/Bolo meter 2014-04-1014 SNU SEMINAR ( 이석천 / 고등과학원 )

15. Instrument : Optics 2014-04-1015 SNU SEMINAR ( 이석천 / 고등과학원 )

16. Instrument 2014-04-1016 SNU SEMINAR ( 이석천 / 고등과학원 )

17. Foreground Removal : Contaminations Contamination sources & Sensitivity 2014-04-1017 SNU SEMINAR ( 이석천 / 고등과학원 )

18. Problems in Foreground Remove Not much is known about the polarization of foregrounds 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 foregrounds 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) 2014-04-1018 SNU SEMINAR ( 이석천 / 고등과학원 )

19. Results 2014-04-1019 SNU SEMINAR ( 이석천 / 고등과학원 )

20. Results : continued 2014-04-1020 SNU SEMINAR ( 이석천 / 고등과학원 )

21. Constraints on Inflation Models I Slow roll parametersObservable quantities in terms of slow roll parameters to first order (Liddle & Lyth 00) 2014-04-1021 SNU SEMINAR ( 이석천 / 고등과학원 )

22. 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) 2014-04-1022 SNU SEMINAR ( 이석천 / 고등과학원 )

23. 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 2014-04-1023 SNU SEMINAR ( 이석천 / 고등과학원 )

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

25. 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 2014-04-1025 SNU SEMINAR ( 이석천 / 고등과학원 )