probing the inhomogeneous universe with gw cosmology...
TRANSCRIPT
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 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)
(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!
� 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!