Science with DECIGO

Naoki Seto (Kyoto U)2008.11.12

The 1st International LISA-DECIGO

Outline• Quick introduction of DECIGO band• ①Stochastic Background from early universe• ②Binary subtraction problem• Other science

– ③Dark energy– ④Intermediate mass black hole (IMBH)

• Summary

DECIGO shares many interesting (and challenging) aspects with LISA and grand-based detectors

LISA

LIGO,VIRGO,LCGT2nd generation

DECIGO

DECIGOcorrelation

Quick Introduction

h~10-23~-24

1Hz

LISA

DECIGO

DECIGOcorrelation

WD+WDconfusion

1/ 2

6 3~ ~110

f G Hzg cm

Frequency (f~1Hz)

High density; compact binaries (NS, stellar mass BH, IMBH,…)

e.g. Farmer & Phinney 03

NS+NS@z=11yr

NS+NSForegroundwith R~105/yr

5/38/3

~10.2 1.2

CGW

Sun

MfT yrHz M

Signal duration (binaries)

Large number (~108) of rotations with frequency evolution

transient

stationary

Individual NS+NS

Deep Window for GWs from Early universe?

16~10GW

Inflation?

Their foreground(to be removed)

DECIGO

correlation

Topics in my talk

①GW fromEarly universe

②Binary Subtractionproblem

③Dark Energy with ~105binaries④IMBH evolution

①Stochastic GW backgroundGW 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 10-15Hz (equal time)

– 0.1Hz: Largely different scale from CMB scale

1/ 2 2inf inf~ ~ ~ ( )h H V energy scale

4( ) ~GW energy scale const

Smith et al.2006

1510GW

Correlation analysisTwo sets of detectors

1 1

22

SS

nhh n

No overlap with LISA

DECIGO

DECIGOcorrelation

(fTobs)1/4

Designed to detect16~10GW

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)3~105/yr~10-3/secOther 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 Tobs x n) / (f x Tobs)

R: merger rateTobs: observational timen: number of fitting parameters for individual binaries~10f: band width ~ freqeuncy

mass, direction,…

~10-3 101 /1=10-2<<1

• large cycle;~108

– need huge number of templates• ~1040 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, Einstein@home,...

• 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…

③Science with NS+NSs• Basic characters

– Huge number: ~105/yr– Excellent clocks– SNR: weak dependence on redshift z

• asymptotically (1+z)1/6– Short GRB? or EMW counterpart

• GW localization: ~1min2 with three sets• redshift estimation

• Dark energy– dL-z relation, only with basic physics– Probes for high redshift universe?

④BH (stellar, intermediate mass)

• IMBH:highly unknown– rate, formation and evolution?– detectable with high SNR even at high-z

• 1000+1000Msun@z=1: SNR>103

• 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: ~105 good clocks available• use them for cosmology and astrophysics

– IMBHs and more