PROBING

THE INHOMOGENEOUS UNIVERSE

WITH GW COSMOLOGY

Kent YagiKyoto University

(Montana State Univ.

from next April)

Amaldi 2011 ＠ Cardiff

7/10 2011

Atsushi Nishizawa (YITP)

Chul-Moon Yoo (YITP)

Collaborators:

§1

INTRODUCTION

§§§§1 Introduction1 Introduction1 Introduction1 Introduction

ΛCDM

CDM

Inhom.

・Cosmological observations

⇒ accelerating expansionof our Universe!

TypeIa SN observation

z

・homogeneous & isotropic

Alnes et al. (2006)

①①①①②②②②

①①①① G.R.+ Dark Energy

②②②② Modified Gravity

③③③③ Inhomogeneous: G.R., no Dark Energy needed.

1111----1 1 1 1 Acceleration of our UniverseAcceleration of our UniverseAcceleration of our UniverseAcceleration of our Universe

1111----2 2 2 2 Inhomogeneous UniverseInhomogeneous UniverseInhomogeneous UniverseInhomogeneous Universe

・We live at the center of void (less dense region).

Density gradient

~Gpc

・Spherically symmetric, dust, inhomogeneous (LTB model)

・Apparent accelerating expansion of the

Universe!

(The simplest example of the inhomogeneous universe model)

・This model can also explain the peaks of CMB & BAO

Garcia-Bellido & Haugboelle (2008)

・We need observables that can probe the LTB void model more clearly! z-drift

・Time evolution of the redshift z

z-drift reflects the accelerating expansion more directly!

FLRW

1111----3 3 3 3 Redshift Drift Redshift Drift Redshift Drift Redshift Drift ΔΔΔΔtttt

zzzz

Loeb (1998)

(1yr obs.)

LTB

LTB with monotonically

increasing density profile:

⇒ ∆tz < 0 for z>0

Quartin & Amendola (2010)

(Kai, Nakao & Yoo

2010)

5yr

10yr

15yr

Quartin & Amendola (2010)

・If ΛCDM is correct

⇒ can reject typical void models with 10yr obs.

・Use absorption lines of quasars (Ly α forest)

(only for high z observation)

1111----4 Measuring z4 Measuring z4 Measuring z4 Measuring z----drift with Edrift with Edrift with Edrift with E----ELTELTELTELT

・To probe ∆tz>0 ⇒ We need low z obs.

GW observation!!

European Extremely Large Telescope (E-ELT)

§2

CONSTRAINING

INHOMOGENEOUS

UNIVERSE WITH

GW OBSERVATIONS

(iii) Larger NS/NS binary detection rate: 106 / yr

(Seto, Kawamura & Nakamura 2001)§2-1 Effect of accelerated expansion in GW waveform

Accelerated. Expansion.

GW

z=0

∆te ∆to

Accelerating. parameter

correctionObs. time

・correction in GW phase：

・Advantages of using DECIGO/BBO over ground-based detectors：

(i) Longer observation time

(ii) Larger numbers of GW cycles: 0.1Hz×5yr~107

NS/NSz

∆t: time to coalescence

加速膨張による補正加速膨張による補正加速膨張による補正加速膨張による補正

Acceleration ××××

Acceleration ○○○○

Am

plitu

de

time

Binary GW

§2-2 Correction in waveform

How accurately can we measure this difference?

§2-3 Numerical Calculations

� circular NS/NS binaries at

z=0~4

� Divide z bin with δz=0.1

� Randomly distributing binaries

at each z bin

(Directions and orientations)

Monte Carlo simulation

� spins

� WD/WD confusion noise

� merger rate evolution based

on star formation galaxy obs.

Event rate: 106/yr

� Motion of Detectors

� Fiducial: ΛCDM

Determining z-drift with DECIGO/BBO using Fisher analysis

K.Y. & A. Nishizawa & C. Yoo (in prep.)

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

0 0.5 1 1.5 2 2.5 3 3.5 4

event rate ∆N(z) [yr-1]

z1

50000

-4

-3

-2

-1

0

1

2

3

0 0.5 1 1.5 2

§2-4 Results1010∆tz

z

Void

ΛCDM5yr

10yr

-4

-3

-2

-1

0

1

2

3

0 0.5 1 1.5 2

5~10yr obs. with DECIGO/BBO

⇒ we can test ∆tz > 0

⇒ we can kill all of the monotonic LTB void model!!(z determined from EM obs.)

-4

-3

-2

-1

0

1

2

3

0 2 4 6 8 10 12 14

1010∆tz

DL(Gpc)

Void

ΛCDM5yr

-4

-3

-2

-1

0

1

2

3

0 2 4 6 8 10 12 14

10yr

z → DL

・We can test ∆tz-DL

with GW observations alone!

§3

DISCUSSIONS

&

SUMMARY

� Direct detection of the acceleration of the Universewith DECIGO/BBO

⇒ 5-10yr obs. can rule out monotonic LTB void models or even general ones!

Space-borne Detectors ⇒ GW Cosmology!!!

Ground-Based Detectors ⇒ GW Astronomy!

Discussions

Summary

Can we probe LTB with arbitrary density profile?

General LTB Void model ⇒ at z=0

(Kai, Nakao & Yoo 2010)

Probing ∆tz > 0 at sufficiently low z

⇒ It seems we can rule out any LTB model!