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COSMIC ACCELERATION Dark 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 . 4/13/2015 NTHU 2012 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 4/13/2015 NTHU 2012 BRIEF OVER VIEW 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 4/13/2015 NTHU 2012 Inconsistencies of standard model EARLY TIMES: Flatness problem Primordial inhomogeneities INFLATION Horizon problem LATE TIMES: Age crisis 4/13/2015 NTHU 2012 AGE CRISIS IN HOT BIG BANG Matter dominated universe: 4/13/2015 NTHU 2012 AGE CRISIS IN HOT BIG BANG Let us ignore gravity for a moment : Present epoch: 4/13/2015 NTHU 2012 AGE CRISIS :Repulsive effect 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! 4/13/2015 NTHU 2012 MS, arXiv: 0904.3445 AGE CRISIS AND ITS RESOLUTION WITH Open universe (K<0) Repulsive effect 4/13/2015 NTHU 2012 AGE CRISIS AND ITS RESOLUTION WITH 4/13/2015 NTHU 2012 ENERGY OF VACUUM SAKHAROV 1968 4/13/2015 NTHU 2012 The effective Cosmological constant 4/13/2015 NTHU 2012 COSMOLOGICAL CONSTANT Wrong formulation Old cosmological constant problem New cosmological constant problem 4/13/2015 NTHU 2012 The correct level of fine tuning 4/13/2015 NTHU 2012 String Landscape We are there! 4/13/2015 NTHU 2012 FINE TUNING PROBLEM : TWO DISTANT SCALES TOGETHER THE BIG AND THE SMALL PUTTING THEM TOGETHER 4/13/2015 NTHU 2012 CINCIDENCE PROBLEM: SHAME 4/13/2015 NTHU 2012 WHERE IS THE COINSIDENCE ? z 4/13/2015 NTHU 2012 SCALAR FIELD AS DARK ENERGY Quintessence 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. 4/13/2015 NTHU 2012 Scalar Field Dynamics in presence of background matter : Tracker or Freezing Models Scaling Solution: MS, Curr Sci, V 97, 848 (2009) [arXiv:0904.3445] 4/13/2015 NTHU 2012 Absence of trackers: Thawing Models 4/13/2015 NTHU 2012 Trackers and non-trackers • 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 . 4/13/2015 NTHU 2012 Quintessence problem C. Kolda and D Lyth, hep-th.9811375 Unstable under radiative corrections when coupled to other fields unless severely fine tuned. 4/13/2015 NTHU 2012 MODIFIED THEORIES OF GRAVITY LARGE SCALE MODIFICATION Chameleon theories. • Galileon modified theories • Massive gravity • Scalar degree(s) of freedom Requirements • Local physics be intact • Cosmic acceleration 4/13/2015 NTHU 2012 SCALARON: Requirements DE: Solar Physics: 4/13/2015 NTHU 2012 Chameleon Field 4/13/2015 NTHU 2012 MASS SCREENING OR FIFTH FORCE SUPPRESSION (Basic Idea) Localized source: Chameleon or Symmetron 4/13/2015 NTHU 2012 Kinetic suppression 4/13/2015 NTHU 2012 Chameleon versus Galileon(Vainshtein ) Chameleon Galileon Small distances: Large distances: 4/13/2015 NTHU 2012 Chameleon at work R, M 4/13/2015 NTHU 2012 Vainstein Effect- dynamical suppression of fifth force Short distances: Large distances: 4/13/2015 NTHU 2012 Vainshtein at work R, M 4/13/2015 NTHU 2012 Symmetron: Dark energy 4/13/2015 NTHU 2012 Symmetron: Dark energy Symmetry should break: Local gravity constraints 4/13/2015 NTHU 2012 Scalar tensor theories -Einstein frame -Jordon frame 4/13/2015 NTHU 2012 Local gravity constraints: Screening Mechanism Chameleon Field 4/13/2015 NTHU 2012 VIABLE f(R) MODELS Stability conditions: Stable de Sitter: Local gravity constraints: 4/13/2015 NTHU 2012 Problems of f(R): scalaron mass Thongkool, MS, R. Gannouji, S.Jhingan, Phys.Rev.D80:043523,2009 ; 4/13/2015 NTHU 2012 CURING THE SINGULARITY ? 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, ChaoQiang Geng, Louis Yang 4/13/2015 NTHU 2012 SELF ACCELERATION:SCOPE OF CHAMELEON THEORIES Self acceleration: Screening: 4/13/2015 NTHU 2012 Chameleon/Symmetron theories- No scope for self acceleration arXiv:1284612: J. Wang, L. Hui and J. Khoury arXiv: 1211.2289: K. Bamba, R. Gannouji, MS 4/13/2015 NTHU 2012 Glimpses of massive gravity (helicity 2 object) + (helicity 1 object)+ (helicity zero object) Universally couples to all fields a b Ghost: Stuckelberging 4/13/2015 NTHU 2012 Best model for quintessential inflation BEST MODEL OF INFLATION AND DARK ENERGY? 4/13/2015 NTHU 2012 NATURE OF DARK ENERGY IT COULD BE ANYTHING OR IT COULD BE NOTHING 4/13/2015 NTHU 2012