Inflation, Primordial Black holes and Gravitational Waves

Transcription

1 Inflation, Primordial Black holes and Gravitational Waves -- Dawn of Gravitational Wave Cosmology -- Misao Sasaki Yukawa Institute for Theoretical Physics, Kyoto University 21 February, 2018 Yukawa International Seminar 2018a (YKIS2018a) "General Relativity -- The Next Generation --"

2 Inflation 2

3 What is Inflation? Brout, Englert & Gunzig 77, Starobinsky 79, Guth 81, Sato 81, Linde 81, Inflation is a quasi-exponential expansion of the Universe at its very early stage; perhaps at t~10-36 sec. It was meant to solve the initial condition (singularity, horizon & flatness, etc.) problems in Big-Bang Cosmology: if any of them can be said to be solved depends on precise definitions of the problems. Quantum vacuum fluctuations during inflation turn out to play the most important role. They give the initial condition for all the structures in the Universe. Cosmic gravitational wave background is also generated. 3

4 温故知新 (learning from the past) ds dt a ( t) dh ; ( 3) 1 a( t) H sinh Ht Creation of Open Universe! Now in the context of String Landscape 4

5 5 From inflation to bigbang After inflation, vacuum energy is converted to thermal energy ( re heating) and hot Bigbang Universe is realized. V(f) ρ Reheating : Γ = H (birth of hot bigbang universe) inflation oscillation slow-roll inflation f inflation t f oscillation (MD) RD t Linde 83,. t R

6 length scales of the inflationary universe targets for multi-freq GW astronomy/cosmology log L L=H 0-1 Size of the Observable Universe L=H cm ~ 46 e-folds 10 8 cm LIGO band (10 2 ~10 7(?) cm) Reheating stage log a(t) Inflationary Universe Hot Bigbang Universe 6

7 from df to curvature perturbation t Mukhanov & Chibisov 81,. Inflation ends/damped osc starts on comoving (f =const.) 3-surface. T const., c 0 hot bigbang universe 0 df 0 end of inflation vacuum fluctuations: df df f 0 x i 0 df 0 On f =const. surface, curvature perturbation appears R c gives rise to gravitational potential perturbation Y : c Y 3 5 H df f f c 7

8 Planck CMB map but important! 1 T Y n v ( small corrections T 3 ) 0 Planck 2013 T K 8

9 Planck TT, TE & EE spectrum 9

10 Planck constraints on inflation Planck 2015 XX V 2 f scalar spectral index: n s ~ 0.96 tensor-to-scalar ratio: r < 0.1 simplest V 2 f model is almost excluded n s r d 1 PT ( k) P ( k) S 3 log[ k PS ( k)] dlog k some element of non-canonicality is needed 10

11 Gravitational Waves from Inflation 11

12 Cosmological GWs scalar field(s) produce density fluctuations -> CMB temp+e-mode fluctuations tensor (GW) fluctuations -> CMB temp+e-mode+b-mode fluct ns E-mode (even parity) B-mode (odd parity) = cannot be produced from density fluctuations CMB B-mode=cosmological GW detector Harvard-Smithsonian Center for Astrophysics LiteBIRD, 12

13 GWs from Standard Inflation direct detection by GW observatories possible? maybe yes or maybe just impossible 13

14 blue-tilted GW spectrum? possible e.g. in massive gravity inflation model Lin & MS (2015) [also in axion-su(2) model Dimastrogiovanni et al. (2016) ] tensor (=GW) spectral index: tensor mass during inflation broad parametric resonance 14

15 inflationary massive gravity: examples Kuroyanagi, Lin, MS & Tsujikawa E 10 GeV M 13 E 310 GeV 10 GeV, M 4 10 M Starobinsky model V with f M M pl 1 exp 4 3M pl m f exp[ 2( f/ M ) ] g pl M 1GeV, low-scale model BBN gives stringent constraints 4 inf V M f, Hend M, 10 M f with mg M 2 pl 4 9 E 310 GeV 15

16 scale-dependent non-gaussianity? Planck XVII f f local NL local NL for 500 WMAP 2010 max for 2500 Planck 2015 max Slightly above 1-s deviation What if this is primordial? may be due to TSS coupling in a massive tensor theory Domenech, Hiramatsu, Lin, MS, Shiraishi, Wang 16 16

17 Gravitational Wave Astronomy/Cosmology 17

18 The Dawn has arrived! LIGO GWs from binary BH merger were detected for the first time on Sep14, 2015 (GW150914). BBH masses: 36 M + 29 M Source redshift: 0.09 (~ 1.2 Glyr) Event rate: /Gpc 3 /yr 18

19 Unusual properties of LIGO-Virgo BHs LIGO-Virgo has detected 5.5 BBH mergers so far. Gw150914,LVT GW170104,GW Many of them seem to be unusually heavy! Any implications? 20 M Their spins seem to be unusually small! 19

20 LIGO BH spins c m s m s n ( m m ): n L / L eff L 1 2 L= L c eff =0 is consistent (exc. GW151226) GW also consistent with zero c eff would be larger if astrophysical origin 20

21 Network of GW Observatories KAGRA will start operation by (ikagra successful, bkagra is under way) LIGO-India has been recently approved by Indian gov. 21

22 Huge advantage in angular resolution Impressive increase from LIGO alone (2) to LIGO+VIRGO (3) +KAGRA (4) +LIGO-India (5) S/N=24 S/N=18.3 (LIGO+Virgo) 22

23 KAGRA KAmioka GRAvitational wave detector In Japanese it is pronounced as Kagura, which means God Music ( 神楽 ) Super-Kamiokande Previously called LCGT Large Cryogenic Gravitational wave Telescope Arm length 3km Cooled to 20K KAGRA KAGRA YITP YITP 23

24 Space-based Future Projects Arm Length DECIGO: 1,000 km launched by ~2030? target freq: ~ 0.1 Hz Deci-hertz Interferometer Gravitational wave Observatory LISA: 2,500,000 km launched by ~2034? target freq: ~10-3 Hz Laser Interferometer Space Antenna 24

25 Multi-freq GW Astronomy Pulsar Timing Array New window to explore the Unknown Universe! Spaced-based Ground-based 25

26 Binary Neutron Star merger found! GW / GRB170817A 26

27 multi-messenger astronomy! 70 observatories include. 7 satellites 27

28 Cosmological Implication! from just a single event! 28

29 Primordial Black Holes 29

30 What are Primordial BHs? PBH = BH formed before recombination epoch (ie at z>>1000) conventionally during radiation-dominated era Hubble size region with dr/r=o(1) collapses to form BH Such a large perturbation may be produced by inflation PBHs may dominate Dark Matter. Carr (1975),. Carr & Lidsey (1991), Ivanov, Naselsky & Novikov (1994),... Origin of supermassive BHs (M 10 6 M ) may be primordial. 30

31 Curvature perturbation to PBH gradient expansion/separate universe approach 2 ( 3) 6H ( t, x) R ( t, x) 16Gr( t, x) Hamiltonian constraint (Friedmann eq.) R G dr c dr c k c c at 2 a 3 r a ( 3) 2 2 H 2 If R ( 3) 0 ( 3) 2 ~ c R H dr r ~ 1 Young, Byrnes & MS 14 M PBH ρh M ( 3 ) 2 ~ H H 1 = a/k, it collapses to form BH t 1s 20M k 1pc 1 Spins of PBHs are expected to be very small R 2 31

32 C hybrid-type inflation grows near the saddle point non-gauss may become large examples non-minimal curvaton Garcia-Bellido, Linde & Wands 96, Domenech & MS 16 Abolhasani, Firouzjahi & MS 11,.. Pattison et al L f ( f) g cc h( f) m c 2 32

33 Constraints on PBHs Can DM be PBHs? f PBH PBH DM LIGO BBHs may occupy ~10% of DM window at g more in Takada-san s talk fig from Inomata et al., Ali-Haimoud & Kamionkowski, Ricotti, Ostriker & Mack ( 08) overestimated the accretion effect 33

34 PBHs as CDM S Pi, YL Zhang, QG Huang, M Sasaki, [ ]. Starobinsky R 2 gravity + non-minimally coupled scalar χ,: V(χ) in the small-field form: ξ-term stabilizes initial condition 34

35 PBH as CDM from the transition stage sharp peak M M PBH M H e H H k a * * * 2 Pl 2( 60N ) * during inflation 1 1 st stage of inflation: N 1 monocromatic PBH mass spectrum critical amplitude f( MPBH ) exp d c 2s ( M H ) extremely sharp peak s ( M ) ( k ) H * 35

36 event rate [Gpc -3 yr -1 ] LIGO BHs = PBHs? MS, Suyama, Tanaka & Yokoyama k 100MeV M PBH 20 M 20 M 1 T kpc PBH merger rate 3-body interaction leads to formation of BH binaries 10 4 f 10 3 LIGO 10 2 fraction of PBH in dark matter tightest constraint at M ~10M (cf. Ali-Haïmoud et al., ) 36 f

37 testing PBH hypothesis Nakamura et al. PTEP 2016 (2016) 093E01 37

38 testing PBH hypothesis 2 Kocsis, Suyama, Tanaka, Yokoyama, arxiv: BBH Merger Rate at time t: mass function P ( m m t) g( m ) g( m ) m : m m m intr intrinsic probability 1, 2, 1 2 t t PBH binary scenario Dynamical formation in dense stellar systems 4 O'Leary et al (2016) clearly distinguishable! 38

39 testing inflation by GW cosmology log L L=H 0-1 Size of the Observable Universe PBH formation cm CMB B-modes cm LIGO PBHs <10 10 cm testing MG? L=H -1 Reheating stage log a(t) Inflationary Universe Hot Bigbang Universe 39

40 Inflation has become the standard model of the Universe Cosmological GWs are the key to confirmation of inflation LIGO-Virgo marked the 1 st milestone in GW astronomy LIGO BHs may be primordial Summary further tests are needed to confirm inflation. The dawn has arrived! advanced GW detectors will prove/disprove the scenario. Multi-band GW astronomy/cosmology has begun! CDM may be PBHs! observational test? GWs will be an essential tool for exploring the Physics of the Unknown Universe! 40

41 So live long and prosper! from STAR TREK 41