Towards%20inflation%20and%20dark%20energy%20cosmologies%20in%20string%20generated%20gravity%20models

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Towards inflation and dark energy cosmologies in
string generated gravity models

• Ishwaree Neupane
• University of Canterbury

March 1, 2006
40th Rencontres de Moriond, La Tuile
18-25 March 2006
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Outlook

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

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Big result in cosmology? still there in 2006?
High-z SNeIa are fainter than expected in an
Einstein-deSitter model

• The case for
• Hubble diagram
• subtraction

Thanks to WMAP and Other Experiments for the
coordinated support
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• Already gt50 dark energy
  proposals in the market!

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Cosmological Concordance Model

• Early Inflation
• de Sitter space
• 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
• between past and future
• between close-by and far-away

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String Compactification?
How to get de Sitter or near de Sitter 4d space?
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Duality Web
Cosmologically Rich
Anti-de Sitter Holography, Brane World
A Remarkable Discovery in Physics (1995/1996)
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Cosmic Acceleration from String Effective Action?

• Heterotic string theory, after its discovery back
  in 1985/86, appeared to be the string theorists
  dream as something like the real word

dilaton
where
modulus
is the Gauss-Bonnet integrand
IPN (with Carter) hep-th/0510109 (PRD/Rapid) ,
hep-th/0512262 (JCAP), hep-th/0602097
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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.
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Frozen dilaton, no modulus coupling

• This simplifies the theory a lot

Define
EOS
EOMs
So Simple!
Different choice of implies different
and hence different potentials! Is it
then all worthy?
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Infinite number of possibilities?
Quadratic/Chaotic
Inverse power-law
Axion
Exponetial
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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
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Including stringy correction
Ansatz
where t can be early or late
Inflationary predictions with
can be significantly different from those with

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

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Generation of Perturbations
U0
In a standard scenario r lt0.43 but with stringy
corrections 0 r lt 0.4
Fixed value of e.g.

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Spectral Index
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Cmbgg OmOl
Nature of the dark energy
CMB

LSS
Recent claim that wlt-1 preferred with evolution
from w0. Alam et al.
Tegmark et al 2004
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Null dominant energy condition energy doesnt
propagate outside the light cone
A model with
negative kinetic energy field
Instabilities cured by higher derivative terms?
string theory?
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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
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Outlook

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

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Thanks for your time.