@ 2012 Miniworkshop for String theory and Cosmology Dec. 01st Seokcheon Lee (KIAS)

APCTP TRP ( 이석천 ) 2 Outline  Motivations of Scalar Tensor Theories of Gravity (STG)  Ambiguities on Jordan Frame (JF) and Einstein Frame (EF)  Observables  Models  Viable Models  Cosmological Tests  Conclusions

Motivations of STG : I APCTP TRP ( 이석천 ) 3  Brans-Dicke Theory (61) : based on Mach’s principle  Universe evolves and so does mass Original Theoretical Motivation

Motivations of STG : II APCTP TRP ( 이석천 ) 4  Existence a ubiquitous fundamental scalar coupled to gravity where unification of gravity with other interactions : String Theories (dilaton), f(R)-gravity (dynamical equivalence with STG), Induced Gravity  Mimic Dark Energy (SL 11), Solution for Li problem in BBN (due to slower expansion than GR before BBN but faster during BBN : A Coc et.al 08), WL (Knox et.al 05), ISW (SL 08), Crossing Phantom (Nesseris et.al 06). Other Theoretical Motivations

Ambiguities on Jordan Frame and Einstein Frame : I APCTP TRP ( 이석천 ) 5  Mathematically two frames are same.  How about physics? Any preferences? Still under debate  However, one should stick on one frame after using one frame for the background evolution. Because

Ambiguities on JF and EF : II APCTP TRP ( 이석천 ) 6 All the background evolutions of the Universe (SuperNovae, Cosmic Microwave Background, Baryonic Acoustic Oscillation, Hubble parameter) are characterized by Hubble parameter, angular distance, and luminosity distance. n = lna = -ln(1+z) Credit by PDG 2012

Perturbed Observables : I CMB . . LSS . . APCTP TRP ( 이석천 )

Perturbed Observables : II Parameter Dependence : CMB  ( reionization optical depth ) : amp litude lowered by  As ( normalization ) : primordial densit y fluctuation  ns : SW plateau l < 40  Maximum compressions = odd peaks : increase as baryon density does  Maximum rarefactions = even peaks : increase as dark matter does APCTP TRP ( 이석천 )

Perturbed Observables : III Parameter Dependence : LSS  Harrison-Zeldovich : ns ≈ 1  As ( normalization ) : primordial densit y fluctuation  keq :  BAO  Below Jean’s length : suppressed by k^4 (impossible to measure) APCTP TRP ( 이석천 )

Models : I APCTP TRP ( 이석천 ) 10  Action of STG  Friedmann equations under FLRW metric  laboratory Cavendish-type effective G Will use model Independent Method : CPL

Models : II APCTP TRP ( 이석천 ) 11  Metric perturbations  Matter perturbations (SL & Ng 11)

Models : III APCTP TRP ( 이석천 ) 12  Background evolution is parameterized by Chevallier- Polarski-Linder parametrization  Matter perturbations is parameterized by growth factor,f with growth index γ

Viable Models ( SL 11 ) APCTP TRP ( 이석천 ) 13

Cosmological Tests ( SL 12 ) APCTP TRP ( 이석천 ) 14

Conclusions APCTP TRP ( 이석천 ) 15  Scalar Tensor gravities can produce many possible background evolutions which mimic dark energy models and other modified gravity models  The growth of the linear matter perturbation can be used to distinguish between models  STG models are strongly limited by the solar system constraint  This might be cured by using general kinetic models  Need to extend to CMB and LSS