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COSMIC ACCELERATION Dark energy and modified theoriesPowerPoint Presentation

COSMIC ACCELERATION Dark energy and modified theories

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### COSMIC ACCELERATIONDark energy and modified theories

M. SAMI

Centre for Theoretical Physics

Jamia Millia University New Delhi

Kobayashi-Maskawa Institute for the Origin of Particles and the Universe,

Nagoya University, Nagoya .

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REFERENCES

- MS, “ A primer on problems and prospects of dark energy “ Curr Sci, V 97, 848 (2009) [arXiv:0904.3445].
- M. Turner, D. Huterer, “Cosmic Acceleration, Dark Energy and Fundamental Physics“J.Phys.Soc.Jap.76:111015,2007.
- E. Copeland, MS, S. Tsujikawa, “ Dynamic of Dark Energy”, hep-th/0603057.
- Zeldovic and Novikov, Structure and evolution of universe, V 2

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Late time inconsistency of hot big bang: Resolution of

age crisis—cosmological constant.

Theoretical issues related cosmological constant (Sakharov)

Coincidence ; Fine tuning.

Quintessence and its problems.

Modified theories of gravity:

Local physics---Screening mechanisms.

Chameleon, Symmetron , Vainshtein mechanism.

Scope of chameleon/symmetron : Self acceleration.

Non-linear massive gravity

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Inconsistencies of standard model

EARLY TIMES:

Flatness problem

Primordial inhomogeneities INFLATION

Horizon problem

LATE TIMES: Age crisis

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Cosmological constant or Hook’s law

Static universe

Neumann (1895) and Seeliger(1896)

Einstein 1917

If no quasi-static universe then away with cosmological constant!

MS, arXiv: 0904.3445

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AGE CRISIS AND ITS RESOLUTION WITH

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The effective Cosmological constant

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COSMOLOGICAL CONSTANTWrong formulation

Old cosmological

constant problem

New cosmological constant problem

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The correct level of fine tuning

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DISTANT SCALES TOGETHER

THE BIG AND THE SMALL

PUTTING THEM TOGETHER

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CINCIDENCE PROBLEM: SHAME

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SCALAR FIELD AS DARK ENERGYQuintessence

for steep pot.

Predictive power of scalar fields

For a priori given cosmic history, it is always possible to construct a field potential

such that it gives rise to the desired result. Thus the scalar field models should be judged

by their generic features.

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Scalar Field Dynamics in presence of background matter : Tracker or Freezing Models

Scaling Solution:

MS, Curr Sci, V 97, 848 (2009) [arXiv:0904.3445]

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Int.J.Mod.Phys.D15:1753-1936,2006, E.Copeland, MS, S Tsujikawa.

Absence of trackers: Thawing Models Tracker or Freezing Models

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Trackers and non-trackers Tracker or Freezing Models

- Trackers (Freezing models): Potentials which mimic steep exponential
- at early epochs and become shallow at late times.

Thawing models:Most of the systems belong to this category

, Scaling Pot.

Phantom field:

A. Sen, HEP0204:048,2002

N Mazumdar, S. Panda, A. Perez-Lorenzana,

Phys.. B614,101(2001)

E.Copeland, M. Garousi, MS, S. Tsujikawa

PRD71:043003,2005, S. Tsijikawa, MS,

PRD71:043003,2005 .

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Quintessence problem Tracker or Freezing Models

C. Kolda and D Lyth,

hep-th.9811375

Unstable under radiative corrections when coupled to

other fields unless severely fine tuned.

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MODIFIED THEORIES OF GRAVITY Tracker or Freezing Models

LARGE SCALE MODIFICATION

- Chameleon theories.
- Galileon modified theories
- Massive gravity
- Scalar degree(s) of freedom

Requirements

- Local physics be intact
- Cosmic acceleration

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Chameleon Field Tracker or Freezing Models

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MASS SCREENING OR FIFTH FORCE SUPPRESSION Tracker or Freezing Models

(Basic Idea)

Localized source:

Chameleon or Symmetron

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Kinetic suppression Tracker or Freezing Models

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Chameleon versus Galileon(Vainshtein ) Tracker or Freezing Models

Chameleon

Galileon

Small distances:

Large distances:

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Vainstein Effect Tracker or Freezing Models- dynamical suppression of fifth force

Short distances:

Large distances:

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Symmetron: Dark energy Tracker or Freezing Models

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Symmetron: Dark energy Tracker or Freezing Models

Symmetry should break:

Local gravity constraints

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VIABLE f(R) MODELS Tracker or Freezing Models

Stability conditions:

Stable de Sitter:

Local gravity constraints:

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Problems of f(R): Tracker or Freezing Modelsscalaron mass

Thongkool, MS, R. Gannouji, S.Jhingan,

Phys.Rev.D80:043523,2009 ;

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CURING THE SINGULARITY ? Tracker or Freezing Models

Countering Term:

Thongkool, MS, S. Rai Choudhury,

arXiv:0908.1663

Thongkool, MS, R. Gannouji, S. Jhingan,

Phys.Rev.D80:043523,2009 ;

S A. Appleby,R. A. Battye, A. Starobinsky,

arXiv:0909.1737

arXiv: 1201.4546, Chung-Chi Lee, Chao-Qiang Geng, Louis Yang

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SELF ACCELERATION: Tracker or Freezing ModelsSCOPE OF CHAMELEON THEORIES

Self acceleration:

Screening:

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Chameleon/Symmetron theories- Tracker or Freezing Models

No scope for self acceleration

arXiv:1284612: J. Wang, L. Hui and J. Khoury

arXiv: 1211.2289: K. Bamba, R. Gannouji, MS

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Glimpses of massive gravity Tracker or Freezing Models

(helicity 2 object) + (helicity 1 object)+ (helicity zero object)

Universally couples to all fields

a

b

Ghost:

Stuckelberging

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Best model for quintessential inflation Tracker or Freezing Models

BEST MODEL OF INFLATION AND DARK ENERGY?

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NATURE OF DARK ENERGY Tracker or Freezing Models

IT COULD BE ANYTHING

OR

IT COULD BE NOTHING

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