Transcript ppt

The origin of “cosmic acceleration”:
void?
backreaction?
modified gravity?
dark energy?
or simply Lambda?
张鹏杰
中国科学院上海天文台
二十一世纪第二个十年的宇宙学
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The standard cosmology
Six parameters describe (almost)
everything (cosmological observations).
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宇宙学探针
宇宙初始条件：微波背景辐射、、中微子背景、引力波背景、、
 膨胀历史和几何
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一型超新星
重子声波振荡
强引力透镜
星系团SZ+X-ray
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年龄（球状星团、星系）
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标准警报、脉泽测距、real
time cosmology、、
 大尺度结构
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弱引力透镜
红移畸变
ISW效应
星系团计数
星系成团性
星系和星系团速度
热SZ和运动学SZ效应
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星系动力学 （kpc-Mpc尺度）、、、
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Uncertainties in modern cosmology
Standard Cosmology
Gaussian, adiabatic,
nearly scale invariant
primordial fluctuations
?
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Dynamical dark energy
GR+SM +Cold dark matter+Cosmological constant
Physical principles
Initial condition of
the universe
?
?2
Nonlinearity in GR,
Nonlinearity in matter
fluid
Gastrophysics
PMG? B-mode?
二十一世纪第二个十年的宇宙学
The observable
universe
? 1
Copernican principle
implies that
the observable universe
is a fair sample of
THE universe
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Unexpected dimming of type Ia supernovae was
first detected in 1998
Riess et al. 1998
Perlmutter et al. 1999
Riess et al. 2005
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What causes the Supernova dimming?
 Violations of the Copernican Principle:
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– What if we live at or near the center of a gigantic
void?
Cosmic acceleration
– The cosmological constant or dynamical dark
energy
– Alternatives:
• GR backreaction(?)
• Modified gravity
Astrophysics:
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– Intrinsic evolution (?); Dust extinction. Compton dimming. [Not
sufficient].....
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(1) LTB: "cosmic acceleration" without dark energy
compensating shell
Low density
region
（void)
background universe
(higher density)
Lemaitre-Tolman-Bondi model:
•The universe has a center
•We live at or near the center
•Matter distribution is isotropic
with respect to and only to the
center (us)
In this radially nhomogeneous
universe, supernovae can appear
dimmer than in a FRW universe,
without cosmic acceleration.
Gravitational
potential
distance
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哥白尼原理的宇宙学检验
• 宇宙微波背景黑体谱检验
M(r), E(r),t_b(r)
– 排除了许多void模型
r
• 星系团运动学SZ效应检验
– 排除了许多void模型
• 背景运动学SZ效应功率谱检验
– 排除了void模型，证实了哥白尼原理
• 除非微调，破坏掉宇宙极早期的均匀性和物质辐射的强耦合
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Testing the Copernican principle
with free electrons as messenger
Goodman 1995;
Caldwell & Stebbins, 2008; Garcia-Bellideo & Haughbolle 2008; ZPJ & Stebbins, 2010
Compton scatterings
allow us to sit at
distant universe and
judge whether CP holds
consequence 1:
T1
e
CMB spectrum will
be non-blackbody
T2
T3
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2008
rules out many
void models
capable of
replacing dark
energy, but not all
of them.
Furthermore, ICS
induces
non-blackbody too.
void density
Void size
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Galaxy clusters (a bunch of electrons) as moving mirrors
CMB frame
Violation of the
Copernican principle
prediction
Dust (matter) frame
 Violation of CP
causes relative
motion between
CMB and the matter
comoving frame
 Causes a large
cluster kSZ effect
In a homogeneous
universe, no
motion between
the two
rules out many
void models
capable of
replacing dark
energy, but not all
of them
observations
Goodman 1995
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The kSZ power spectrum measurement rules out void models
Copernican principle is confirmed
Cosmic acceleration is REAL!
The Hubble bubble model
13 uk^2 (SPT)->8 uk^2(ACT)->6.5 uk^2(SPT)
Background universe
Compensating shell
void
at l=3000, a few arcminute
二十一世纪第二个十年的宇宙学
ZPJ & Stebbins 2010
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So, cosmic acceleration is REAL!
But what causes it?
– Mirage of GR backreaction?
– Infrared corrections to GR?
– Cosmological constant/dark energy?
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(2) GR backreaction on the background expansion
Backreaction
eff
uv
T
Tuv  Guv ( gab )
 Tuv  Guv ( g
FRW
Tuv  Guv ( g ab
FRW
ab
)
Exact equation
Usual approximation
2

G

Guv 2
1
FRW
uv
 hab )  Guv ( g ab ) 
hab 
hab  L
2
g ab
2 g ab
A century old topic, still highly controversial!
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(3) Modified gravity and the cosmic acceleration
 f(R)
 DGP
 该领域研究在过去十年出现了长足进展
– New/old models: f(T), cascading gravity, Galileo gravity,
Einstein-Ather, etc. Refer to the review article by Jain & Khoury,
2010
– N-body codes/simulations! (e.g. Oyaizu 08; Fabian et al. 0811; Chan & Scoccimarro 09; Zhao et al. 01)
– Fundamental features/impacts:
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Gravity is environmental depenent
Screening mechanisms required
Violation of the Birkhoff theorem
Violation of equivalence principle (apparent or real)
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广义相对论的宇宙学检验
 宇宙膨胀历史+宇宙大尺度结构+太阳系检验
– 具体模型的检验
– 参数拟合
– Smoking guns
二十一世纪第二个十年的宇宙学
SN Ia, BAO,CMB
Jain & Khoury 2010
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Testing specific models: expansion and DGP
DGP is disfavored comparing to LCDM
Zhu & Alcaniz 2004
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Song et al. 2006
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CMB and DGP
Fang et al. 2008
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Redshift distortion and DGP
f=dlnD/dlna
Blake et al. 2010
Guzzo et al. 2008
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参数化引力的宇宙学数据拟合
Gong-Bo Zhao et al. 2010
Daniel et al. 2010
一般2个参量，分别描述物质
弯曲时空的总能力和弯曲时间
、空间的相对能力
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galaxy-lensing 2 (   )
EG 

galaxy-velocity

检验宇宙学尺度上的
广义泊松方程
ZPJ et al. 2007
BigBOSS can improve
by a factor of 10
Reyes et al. 2010
The first E_G measurement: confirmed GR at ~10-40 Mpc/h scales
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The origin of “cosmic acceleration”:√
Void?
X
Backreaction?
X?
Modified gravity?
??
Dynamical dark energy?
or simply Lambda?
二十一世纪第二个十年的宇宙学
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√?
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CMB
In O(10) years, hopefully we are
able to put everything together to
reconstruct the elephant.
lensing
peculiar velocity
the dark
universe
SNe Ia
BAO
cluster abundance
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Systematics, Systematics, Systematics
•Theory
•The dark degeneracies!
•Unbiased parametrizations
•Calculation
•Nonlinearity and gastrophysics
•N-body and hydro simulations
•Measurement
•SN Ia: evolution? sub-types? Dust
statistical
error
extinction? ..
•Cluster: mass-flux scaling relation...
•Weak lensing: PSF, intrinsic
alignment, photo-z...
•Redshift distortion: high order
coupling, velocity bias, distant
observer....
•BAO: nonlinearity, scale dependent
bias
•.....
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