Towards inflation and dark energy cosmologies in string generated gravity models Ishwaree Neupane University of Canterbury March 1, th Rencontres de Moriond, La Tuile March 2006

Outlook The 20 th Century Physics The 20 th Century Physics General Relativity vs Quantum Mechanics General Relativity vs Quantum Mechanics The Physics of 80’s and 90’s The Physics of 80’s and 90’s String Theory: A Theoretical Balancing Act String Theory: A Theoretical Balancing Act Ingredients: Extra Dimensions, Supersymmetry Ingredients: Extra Dimensions, Supersymmetry String/M Theory: One Mo’ Time! String/M Theory: One Mo’ Time! Beyond perturbative approach: Branes, Fluxes, Cycles Beyond perturbative approach: Branes, Fluxes, Cycles Inflation, Dark Energy and Opportunities Inflation, Dark Energy and Opportunities

Big result in cosmology? still there in 2006? High-z SNeIa are fainter than expected in an Einstein-deSitter model The case for 1)Hubble diagram 2)subtraction Thanks to WMAP and Other Experiments for the coordinated support

Already >50 dark energy proposals in the market! Already >50 dark energy proposals in the market!

Cosmological Concordance Model Early Inflation Early Inflation de Sitter space de Sitter space During 10^{-30} sec During 10^{-30} sec Current Acceleration Near de Sitter space During few billion years The ultimate laws of Nature might contain a fundamental and simple, concise relation The ultimate laws of Nature might contain a fundamental and simple, concise relation between past and future between close-by and far-away

String Compactification? How to get de Sitter or near de Sitter 4d space?

Duality Web Cosmologically Rich Anti-de Sitter Holography, Brane World A Remarkable Discovery in Physics (1995/1996)

Cosmic Acceleration from String Effective Action? Heterotic string theory, after its discovery back in 1985/86, appeared to be the string theorist’s dream as something like the real word Heterotic string theory, after its discovery back in 1985/86, appeared to be the string theorist’s dream as something like the real word where is the Gauss-Bonnet integrand IPN (with Carter) hep-th/ (PRD/Rapid), hep-th/ (JCAP), hep-th/ dilaton modulus

In a known example of string compactification Unfortunately, we do not have a precise knowledge about the field potential. Any such potential might take into account the non-perturbative effects, as arising from the effects of branes/fluxes present in the extra dimensions.

Frozen dilaton, no modulus coupling This simplifies the theory a lot This simplifies the theory a lot Define EOMs Different choice of implies different and hence different potentials! Is it then all worthy? So Simple! EOS

Infinite number of possibilities? Quadratic/Chaotic Inverse power-law Axion Exponetial

The issue is not merely to achieve For the model to work a scalar field should relax its potential energy after inflation down to a sufficiently low value, presumably very close to the observed value of the dark energy

Including stringy correction Ansatz where ‘t’ can be early or late Inflationary predictions with can be significantly different from those with

The solution is where

Late-time Acceleration is possible The solution is modelled such that

Generation of Perturbations Fixed value of e.g. U=0 In a standard scenario r <0.43 but with stringy corrections 0 ~ r < 0.4

Spectral Index

Cmbgg OmOl CMB + LSS Nature of the dark energy Tegmark et al 2004 Recent claim that w<-1 preferred with evolution from w=0. Alam et al.

Null dominant energy condition: energy doesn’t propagate outside the light cone A model with negative kinetic energy field negative kinetic energy field Instabilities cured by higher derivative terms? string theory? …

Phantom  Non-phantom Cosmology? In the absence of (or trivial) scalar GB coupling, a transition between non-phantom and phantom cosmology is unlikely, but this is possible, e.g., with Gauss-Bonnet coupling

Outlook Next 5-10 years dark sector of cosmology research will remain exciting to understand the theory of inflation and dark energy universe.

Thanks for your time….