The origin of cosmic acceleration void backreaction modified gravity dark energy or simply lambda
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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. The standard cosmology. Six parameters describe (almost) everything (cosmological observations). 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 一型超新星 重子声波振荡

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张鹏杰 中国科学院上海天文台

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The origin of cosmic acceleration void backreaction modified gravity dark energy or simply lambda

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


The standard cosmology

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

    • 一型超新星

    • 重子声波振荡

    • 强引力透镜

    • 星系团SZ+X-ray

    • 、、

    • 年龄(球状星团、星系)

    • 、、

    • 标准警报、脉泽测距、real time cosmology、、

  • 大尺度结构

    • 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

    • 、、、

星系动力学 (kpc-Mpc尺度)、、、

二十一世纪第二个十年的宇宙学


Uncertainties in modern cosmology

Uncertainties in modern cosmology

3

Dynamical dark energy

?

Standard Cosmology

Gaussian, adiabatic,

nearly scale invariant

primordial fluctuations

GR+SM

+Cold dark matter+Cosmological constant

The observable

universe

Physical principles

Initial condition of

the universe

?

2

Nonlinearity in GR,

Nonlinearity in matter fluid

Gastrophysics

?

1

?

Copernican principle

implies that

the observable universe

is a fair sample of

THE universe

PMG? B-mode?

二十一世纪第二个十年的宇宙学


Unexpected dimming of type ia supernovae was first detected in 1998

Unexpected dimming of type Ia supernovae was first detected in 1998

Riess et al. 1998

Perlmutter et al. 1999

Riess et al. 2005

二十一世纪第二个十年的宇宙学


What causes the supernova dimming

What causes the Supernova dimming?

1

  • Violations of the Copernican Principle:

    • 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:

    • Intrinsic evolution (?); Dust extinction. Compton dimming. [Not sufficient].....

2

3

二十一世纪第二个十年的宇宙学


1 ltb cosmic acceleration without dark energy

(1) LTB: "cosmic acceleration" without dark energy

  • 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.

compensating shell

Low density

region

(void)

background universe

(higher density)

Gravitational

potential

distance

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哥白尼原理的宇宙学检验

M(r), E(r),t_b(r)

  • 宇宙微波背景黑体谱检验

    • 排除了许多void模型

  • 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

r

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Testing the Copernican principle with free electrons as messengerGoodman 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:

CMB spectrum will

be non-blackbody

T1

e

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

二十一世纪第二个十年的宇宙学


Galaxy clusters a bunch of electrons as moving mirrors

Galaxy clusters (a bunch of electrons) as moving mirrors

CMB frame

Dust (matter) frame

Violation of the

Copernican principle

prediction

  • 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 modelsCopernican principle is confirmedCosmic acceleration is REAL!

13 uk^2 (SPT)->8 uk^2(ACT)->6.5 uk^2(SPT)

The Hubble bubble model

Background universe

Compensating shell

void

at l=3000, a few arcminute

ZPJ & Stebbins 2010

二十一世纪第二个十年的宇宙学


So cosmic acceleration is real

So, cosmic acceleration is REAL!

  • But what causes it?

    • Mirage of GR backreaction?

    • Infrared corrections to GR?

    • Cosmological constant/dark energy?

二十一世纪第二个十年的宇宙学


2 gr backreaction on the background expansion

(2) GR backreaction on the background expansion

Exact equation

Backreaction

Usual approximation

A century old topic, still highly controversial!

二十一世纪第二个十年的宇宙学


3 modified gravity and the cosmic acceleration

(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. 08-11; Chan & Scoccimarro 09; Zhao et al. 01)

    • Fundamental features/impacts:

      • 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

SN Ia, BAO,CMB

Jain & Khoury 2010

二十一世纪第二个十年的宇宙学


Testing specific models expansion and dgp

Testing specific models: expansion and DGP

DGP is disfavored comparing to LCDM

Zhu & Alcaniz 2004

Song et al. 2006

二十一世纪第二个十年的宇宙学


Cmb and dgp

CMB and DGP

Fang et al. 2008

二十一世纪第二个十年的宇宙学


Redshift distortion and dgp

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

二十一世纪第二个十年的宇宙学


The first e g measurement confirmed gr at 10 40 mpc h scales

检验宇宙学尺度上的

广义泊松方程

The first E_G measurement: confirmed GR at ~10-40 Mpc/h scales

ZPJ et al. 2007

BigBOSS can improve

by a factor of 10

Reyes et al. 2010

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X

The origin of “cosmic acceleration”: Void? Backreaction? Modified gravity? Dynamical dark energy? or simply Lambda?

X?

??

??

√?

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In O(10) years, hopefully we are able to put everything together to reconstruct the elephant.

CMB

lensing

peculiar velocity

the dark universe

SNe Ia

BAO

cluster abundance

二十一世纪第二个十年的宇宙学


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 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

    • .....

Systematics, Systematics,Systematics

statistical error

二十一世纪第二个十年的宇宙学


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