Primordial Black holes and Gravitational Waves

Transcription

1 Primordial Black holes and Gravitational Waves Misao Sasaki Yukawa Institute for Theoretical Physics, Kyoto University COSMO-17, 1 September, 2017

2 Primordial Black Holes 2

3 What are Primorial BHs? PBH = BH formed before recombination epoch (ie at z>>1000) conventionally during radiation-dominated era Hubble size region with forms PBH Such a large perturbation may be produced by inflation PBHs may dominate Dark Matter. O( 1) Carr (1975),. Carr & Lidsey (1991), Ivanov, Naselsky & Novikov (1994),... Origin of supermassive BHs (M 10 6 M ) may be primordial. 3

4 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 ( ) g h( ) m 2 4

5 Curvature perturbation to PBH gradient expansion/separate universe approach 2 ( 3) 6H ( t, x) R ( t, x) 16G( t, x) Hamiltonian constraint (Friedmann eq.) R G c c k c c at 2 a 3 a ( 3) 2 2 H 2 If R ( 3) 0 ( 3) 2 ~ c R H ~ 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 5

6 Accretion to PBH? Bondi accretion 2 4 : / 1/ 3 GM M rb cs cs P, rb, () 1 2 ~ O c accretion rate/hubble time 4 c am HM H GH H a 3 M 3 H 3 M 1 s H : M csh M, 4 M 3 2 M M a M M da 3 M H a 8 horizon size at the time of PBH formation PBH mass can increase by a factor of 1.5 at most Mass increase can be ignored, given other ambiguities s 2 6

7 Effect on CMB? accretion can lead to radiative emission Eddington luminosity: max luminosity from accretion L 4 GMm c p edd ; edd T L L ; 1 m energy output/hubble time T p = proton mass = Thomson cross section luminosity from PBH 4 4 R npbh L Gm Gm PBH a fp BH H H H a H 3 4 a PBH 10 f PBH ; fpbh a eq CDM edd p p R R R T eq T eq small, but may not be entirely negligible 3 7

8 Constraints on PBHs DM can t be dominated by PBHs! opinion varies though..., particularly at M ~ 100M f PBH PBH DM Carr et al Ali-Haimoud & Kamionkowski, Ricotti, Ostriker & Mack ( 08) overestimated the accretion effect 8

9 Gravitational Waves from Inflation 9

10 length scales of the inflationary universe targets for multi-frequency GW astronomy 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 10

11 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 Source: Harvard-Smithsonian Center for Astrophysics 11

12 GWs from Standard Inflation could direct detection by GW observatories possible? maybe yes or maybe just impossible 12

13 2 nd order GW constraints on PBH Non-negligible PBH formation means h 3Hh a h S 2 ij ij ij ij GWs are produced with amplitude: 2 k hij ( ) ( ) 2 2 S k S k ah Saito & Yokoyama 09, Alabidi et al. 12, ( ) k S 2 1 k Sij 2 i c ( ) j c 2 S k a a 2 nd order GWs would dominate at f>10-10 Hz (k>10 4 Mpc -1 ) 2 5 ( PBHh, M PBH ) ( 10, 100M ) 20 ( 0. 1, 10 g) 13

14 tensor (=GW) spectral index: blue-tilted GW spectrum? possible in inflationary massive gravity Lin & MS 15 Kuroyanagi, Lin, MS & Tsujikawa 17 (in prep) 14

15 Gravitational Wave Physics/Astronmy 15

16 The Dawn has arrived! GWs from binary BH merger were detected for the first time on Sep14, 2015 (GW150914). LIGO BBH masses: 36 M + 29 M Source redshift: 0.09 (~ 1.2 Glyr) Event rate: /Gpc 3 /yr 16

17 Unusual properties of LIGO BHs LIGO has detected 3BBH mergers (+1 candidate) so far. They seem to be unusually heavy! (exc. GW151226) Any implications? Their spins seem to be unusually small! 20 M 17

18 LIGO BH spins m s m s n ( m m ): n L / L eff L 1 2 L= L eff =0 is consistent (exc. GW151226) eff would be larger if of astrophysical origin 18

19 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 Nakamura, MS, Tanaka & Thorne LIGO 10 2 fraction of PBH in dark matter 19

20 testing PBH hypothesis Nakamura et al. PTEP 2016 (2016) 093E01 20

21 Network of GW Observatories VIRGO has just begun to take data (on 1 st Aug!) KAGRA will start operation by 2019~2020 (ikagra has started!) LIGO-India has been recently approved by Indian gov. 21

22 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 APCTP KAGRA KAGRA YITP NCTS YITP 22

23 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: 5,000,000 km launched by ~2034? target freq: ~10-3 Hz Laser Interferometer Space Antenna 23

24 B-mode Space-based Projects r PT ( k) P ( k) S 1 (at k 0.05 Mpc ) : tensor-to-scalar ratio LiteBIRD (~ 2025) Lite (light) Satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection EPIC (~2030?) Experimental Probe of Inflationary Cosmology 24

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

26 testing inflation by GW astronomy log L L=H 0-1 Size of the Observable Universe PBH formation? cm CMB B-modes cm LIGO BHs=PBHs? <10 10 cm testing MG? L=H -1 Reheating stage log a(t) Inflationary Universe Hot Bigbang Universe 26

27 Summary Inflation has become the standard model of the Universe. Cosmological GWs are the key to confirmation of inflation. LIGO detection of GWs marked the 1 st milestone in GW physics/astronomy. The Dawn has arrived! LIGO BHs may be primordial: advanced GW detectors will prove/disprove the scenario. Multi-frequency GW astronomy/astrophysics is arriving soon. GWs will be an essential tool for exploring the Physics of the Unknown Universe 27