Bridging the Gap between Terrestrial Detectors and LISA

Elba 2002

May 24, 2002

Seiji Kawamura

National Astronomical Observatory of Japan

Contents

1. Introduction

2. What is DECIGO?

3. Science obtained by DECIGO

4. Sensitivity of DECIGO

5. Current Status of DECIGO

6. Summary

Gap between Terrestrial Detectors and LISA

10-18

10-24

10-22

10-20

10-4 10410210010-2

Frequency [Hz]

Str

ain

[H

z-1/2] LISA

Terrestrial Detectors(e.g. LCGT)Gap

Importance of Bridgingthe Gap

New window brings new science! Observe inspiral sources that have moved abov

e the LISA band Observe inspiral sources that have not yet mov

ed into the ground-based detector band Completely new sources could be detected Completely new science could be obtained

How to bridge the gap?

Improve the low-frequency sensitivity of terrestrial detectors

Improve the high-frequency sensitivity of LISA

Build a detector suitable for the gap frequency DECIGO

What is DECIGO? Deci-hertz Interferometer Gravitational Wave Observatory Space Antenna with short arm length

10-18

10-24

10-22

10-20

10-4 10410210010-2

Frequency [Hz]

Str

ain

[H

z-1/2] LISA

Terrestrial Detectors(e.g. LCGT)

DECIGO(Sensitivity: Arbitrary)

DECIGO

Named by T. Nakamura in the PRL paper by N. Seto, S. Kawamura, and T. Nakamura

Potential candidate for the future Japanese space antenna

Study of DECIGO just started; still primitive

Relationship between Sensitivity and Arm Length

10-18

10-21

10-19

10-20

Frequency [Hz]

Str

ain

[H

z-1/2] LISA

10-4 10210010-2

DECIGO

Shot Noise (f<f0): XSN/L P∝ -1/2/L (L∝ -2) -1/2/L=L/L

(Arm Length:

x100

f0 f01/100 of LISA)

Force Noise:

x100

XFN/L 1/L∝ f0:1/L

f1f-2

Advantages of DECIGONo confusion limiting noise above 0.1Hz

(From the LISA report)

Acceleration of Expansion of the Universe

NS-NS (z～1)

GW

DECIGO

Output

Expansion ＋ Acceleration?

Time

Str

ain

Template (No Acceleration)

Real Signal ?Phase Delay～ 1sec (10 years)

Seto, Kawamura, Nakamura, PRL 87, 221103 (2001)

Ultimate Sensitivity of DECIGO

Frequency [Hz]10-4 10410210010-2

Str

ain

[H

z-1/2]

LISATerrestrial Detectors(e.g. LCGT)

Ultimate DECIGO

10-18

10-24

10-22

10-20

10-26 M=100kg, L=5×108m)(Quantum noise limited

DECIGO(LISA Technology

L=5×107m)

Ultimate DECIGO × 1000(Necessary for

acceleration measurement)

In the Paper, we said… The ultimate sensitivity of a space antenna in th

e far future could be, however, 310-27 around 0.1 Hz in terms of strain, assuming the quantum limit sensitivity for a 100 kg mass and an arm length of 1/10 of LISA. We name this detector DECIGO.

This requires an enormous amount of effective laser power, and also requires that the other noise sources, such as gravity gradient noise, thermal noise, practical noise, etc. should be all suppressed below the quantum noise. Here we assume that such an antenna may be available by the end of this century.

How to Improve Sensitivity?

Increase effective power - Increase the laser power

- Increase the diameter of mirror

Use shorter wavelength? Reduce other sensing noise Reduce force noise Solve confusion limiting noise problem

DECIGO Working Group

NAOJ does not have a definitive plan after ALMA.

Convened in 2002 as one of WGs to study the future project candidates for NAOJ

1st Meeting held on May 9, 2002 80 members currently involved To be discussed in the 2nd Symposium (June 4-

5, 2002) for NAOJ future projects

Summary It is important to bridge the gap between

terrestrial detectors and LISA. DECIGO is a candidate for the Japanese space

antenna. There is no WD-WD confusion limiting noise

above 0.1 Hz. DECIGO could measure the acceleration of

expansion of the Universe. DECIGO-WG has just started investigating the

possibility.