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Late-time Cosmology with String Gases

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Anisotropy and dilaton play vital role in stabilization. Late-time Cosmology. Scale of ... (e.g. pressure and anisotropy are missing? ... – PowerPoint PPT presentation

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Title: Late-time Cosmology with String Gases


1
Late-time Cosmology with String Gases
  • Scott WatsonDepartment of PhysicsBrown
    Universitywatson_at_het.brown.edu

2
Challenges for Cosmology
  • Dark Energy / Cosmological Constant
  • Dark Matter
  • Viable Inflation model (or alternative)
  • Singularities
  • String Theory?
  • Extra Dimensions (316)
  • Massless Moduli (a.k.a Determining the
    Landscape)

3
Why Three Large Dimensions?
Brandenberger-Vafa Scenario
Strings intersect in at most 3 spatial
dimensions!!!
4
Too Much Symmetry?
5
Moduli Space
  • d2 moduli (metric and NS flux)
  • No potentials in low energy theory
  • We want to generate potential using massive
    string modes.

6
String Gas Cosmology
Generate potential for massless string modes by
including backreaction of massive string modes.
(Brandenberger, Vafa) and (Tseytlin, Vafa)
7
Stabilization at the self dual radius
Assuming that the 6 compactified dimensions begin
at the self-dual point, we find that they remain
frozen for all times as the other 3 dimensions
grow large.
Only constraint on dilaton is that gssmall Our
result holds for all initial values of f given
this constraint.
3d expanding
6d stabilized
8
Anisotropy and dilaton play vital role in
stabilization
9
Late-time Cosmology
10
Successes of String Gas Approach
  • Explanation for origin of 316 universe
  • Isotropization is natural result of dynamics
    (hep-th/0207168, Brandenberger and GSW)
  • 6d Stabilized near self dual radius
    (hep-th/0307044 , Brandenberger and GSW)
  • Stable to linear perturbations ( long
    wavelength hep-th/0312097, Brandenberger and GSW
    ) ( small wavelength hep-th/0402015, GSW )
  • Possibility of Cold Dark Matter from remnant
    strings in the extra dimensions (hep-th/0402225,
    Gubser and Peebles)
  • String Gas approach can be extended to late time
    cosmology (hep-th/0403075 , Battefeld and GSW)

11
Upshot
  • Higher dimensional perspective is
    different.(e.g. pressure and anisotropy are
    missing?)
  • Non-perturbative physics important NOT just
    massless modes.

12
String Higgs Effect
  • At special places in the landscape massive states
    become massless and should be included in low
    energy effective action
  • Generate trapping potential by their coupling
    to the other massless states (Should include ALL
    massless states hep-th/9401139 )

13
Worldsheet Perspective
14
Compactification on S1
15
Enhanced Gauge Symmetry
At self dual radius there are additional massless
states
Additional states carry winding and momentum
charge
16
String Higgs Effect
17
String Higgs Effect in Cosmology(hep-th/0404177,
GSW)
18
String Higgs Effect in Cosmology
Particle Production near ESP
States easy to produce at ESP. Additional states
lead to backreaction on sigma
19
Moduli Trapping
This is another realization of Moduli Trapping
(hep-th/0403001, Kofman, et. al.)
20
Comments and Conclusions
  • Dimensionality as result of string dynamics
  • Cosmology and non-perturbative physics may offer
    solution to string theory landscape.
  • Many applications of moduli trapping (Reheating,
    Dark Matter, Cyclic/Ekpyrotic, Brane Inflation
    models, etc)
  • Interesting alternative to LCDM (Gubser,
    Peebles SW, Battefeld)
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