Science with DECIGO Naoki Seto (Kyoto U) The 1st International LISA-DECIGO

Outline Quick introduction of DECIGO band ① Stochastic Background from early universe ② Binary subtraction problem Other science – ③ Dark energy – ④ Intermediate mass black hole (IMBH) Summary DECIGO shares many interesting (and challenging) aspects with LISA and grand-based detectors

LISA LIGO,VIRGO,LCGT 2 nd generation DECIGO correlation Quick Introduction h~10 -23~-24 1Hz

LISA DECIGO correlation WD+WD confusion Frequency (f~1Hz) High density; compact binaries (NS, stellar mass BH, IMBH,…) e.g. Farmer & Phinney 03

1yr NS+NS Foreground with R~10 5 /yr Signal duration (binaries) Large number (~10 8 ) of rotations with frequency evolution transient stationary

Individual NS+NS Deep Window for GWs from Early universe? Inflation? Their foreground (to be removed) DECIGO correlation

Topics in my talk ① GW from Early universe ② Binary Subtraction problem ③ Dark Energy with ~10 5 binaries ④ IMBH evolution

① Stochastic GW background GW propagation: almost no interaction, not easy to detect, But a crucial fossil from very Early universe!! NASA

GW from Inflation An important prediction of inflation –Origin: Quantum fluctuation –Energy scale of inflation –Nearly flat spectrum above Hz (equal time) –0.1Hz: Largely different scale from CMB scale

Smith et al.2006

Correlation analysis Two sets of detectors No overlap with LISA DECIGO correlation (fT obs ) 1/4 Designed to detect Interesting level with current constraints But Tinto et al. 01, Hogan & Bender 01 DECIGO

② Foreground cleaning is essential! Individual NS+NS NS,BH binaries NS+NS merger rate: ~(10/yr)x(10Gpc/300Mpc) 3 ~10 5 /yr~10 -3 /sec Other potential foregrounds popIII SNe,…..? (might be a problem) An inevitable problem for GW astronomy Can we remove NS+NSs?

In principle, Yes (total fitting parameters)/(data amount) ~(R x T obs x n) / (f x T obs ) R: merger rate T obs : observational time n: number of fitting parameters for individual binaries~10 f: band width ~ freqeuncy mass, direction,… ~ /1=10 -2 <<1

large cycle;~10 8 –need huge number of templates ~10 40 templates for 1yr integration –full coherent integration; difficult even with Moore’s law extrapolated to ~2020 need efficient detection method –LISA(WD+WD, EMRI), LIGO-pulsar search »mock LISA data challenge, requirement for detector sensitivity and configuration –must detect them in short integration time –no dead angles –ongoing: careful evaluation for sensitivity and configuration Cuter&Harms 06 (for BBO) In reality…

③ Science with NS+NSs Basic characters –Huge number: ~10 5 /yr –Excellent clocks –SNR: weak dependence on redshift z asymptotically (1+z)1/6 –Short GRB? or EMW counterpart GW localization: ~1min 2 with three sets redshift estimation Dark energy –d L -z relation, only with basic physics –Probes for high redshift universe?

④ BH (stellar, intermediate mass) IMBH:highly unknown –rate, formation and evolution? –detectable with high SNR even at high-z M SNR>10 3 clue to understand SMBH? BH+NS –test for general relativity (Yagi)

Summary Interesting science with DECIGO –GW background form early universe 1Hz: (potential) deep window for GWs direct detection of inflation background(?), …. –Foreground cleaning is essential!! LISA (WD+WD,EMRI), Ground-base (unknown pulsars) –NS+NS: ~10 5 good clocks available use them for cosmology and astrophysics –IMBHs and more