Cosmological Expansion from Nonlocal Gravity Correction - PowerPoint PPT Presentation

Loading...

PPT – Cosmological Expansion from Nonlocal Gravity Correction PowerPoint presentation | free to download - id: 1bbc77-MDA1N



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Cosmological Expansion from Nonlocal Gravity Correction

Description:

Cosmological Expansion from Nonlocal Gravity Correction. Tomi Koivisto, ITP Heidelberg ... 5. Radiation domination 6. Matter domination. 7. Acceleration 8. ... – PowerPoint PPT presentation

Number of Views:50
Avg rating:3.0/5.0
Slides: 14
Provided by: vir113
Learn more at: http://www.physik.uni-bielefeld.de
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Cosmological Expansion from Nonlocal Gravity Correction


1
Cosmological Expansion from Nonlocal Gravity
Correction
3rd Kosmologietag at IBZ, Bielefeld, May 8-9, 2008
Tomi Koivisto, ITP Heidelberg
e-Print arXiv0803.3399, to appear in PRD
1. Outline Introduction 2. Nonlocalities in
physics 3. The gravity model 4. Scalar-tensor
formulation Dynamics 5. Radiation domination 6.
Matter domination 7. Acceleration 8.
Singularity 9. Summary Constraints 10. Solar
system 11. Perturbations 12. Ghosts
Conclusions
2
Nonlocalities in physics
  • Nonlocality lt-gt Infinite number of derivatives
  • Interactions at x not
    d(x)
  • String field theory is nonlocal
  • Since strings are extended
    objects

-BH information paradox requires nonlocal
physics?
Susskind J.Math.Phys.366377-6396,1995
  • Gravity as an effective theory
  • Leading quantum
    corrections nonlocal!

t Hooft Veltman Annales Poincare
Phys.Theor.A2069-94,1974
3
Nonlocal gravity modification
- Thus, consider the class of simple modications
- Like a variable G
- When f(x)cx, could stabilize the Euclidean
action
C. Wetterich Gen.Rel.Grav.30159-172,1998
- Recent suggestion could provide dark energy
S. Deser R.P. Woodard Phys.Rev.Lett.99111301,2
007.
...then f should be about -1. Its argument is
dimensionless -gt fine tuning alleviated ?
4
scalar-tensor formulation
Bi-
Introduce a field and a Lagrange multiplier
Define
- Equivalent to a local model with two extra
d.o.f ! - Massless fields with a nonlinear sigma
-type (kinetic) interaction
5
Cosmology Radiation domination
In the very early universe the correction
vanishes
As matter becomes non-relativistic
- BBN constrains the corrections during RD
- The possible effects are a
consequence of the onset MD
6
Dust dominated era
Approximate solution
Assume f(x) Nxn
- If ngt0, the coupling grows
- If N(-1)nlt0, the nonlocal contribution to
energy grows
7
Solutions
One may reconstruct f(x) which gives the assumed
expansion!
But, assuming power-law f(x)Nxn, the expansion
goes like
- For larger n the evolution is steeper (here
n3,n6) - N is roughly of the
order (0.1)(n1) in Planck units
8
Singularity
Power-law and exponential f(x) which result in
acceleration lead to a sudden future singularity
at tt_sgtt_0
Barrow, Class.Quant.Grav. 21 (2004) L79-L82
- Density (and expansion rate) remain
finite at t_s
- Pressure (and acceleration rate) diverge at
t_s
Possible resolutions
1) Simply reconstruct different f(x) resulting in
finite w 2) Regularize the
inverse dAlembertian! 3) Consider higher
curvature terms
9
Summary of cosmic evolutions
ngt0
f(x)Nxn
Nonlocal effect
N(-1)ngt0
N(-1)nlt0
nlt0
Slows down expansion
Acceleration
Matter domination
Regularized
Singularity
?
10
Solar system constraints
- If the fields are constant
- Where the corrections to the Schwarzschild
metric are
- Exact Schwarzschild solution R0, fields
vanish - They are second order in GM/r lt
10(-6) - Seems they escape the constraints on
G_/G, ?-1 10(-5)
11
Perturbation constraints
- In the cosmological Newtonian gauge
- Effective anisotropic stress appears
(relevant for weak lensing?)

- Poisson equation is different too
(detectable in the ISW?)
- Matter growth is given by the G_
(constraints from LSS !)
12
Ghost constraints
  • From
  • one sees that graviton is not ghost when (1?)gt0.
  • The Einstein frame,
  • one may use the general result for quadratic
    kinetic Lagrangians L (valid when Lgt0)
  • two decoupled perturbation d.o.f propagating at c

Langlois Renaux-Petel JCAP 0804017,2008
- Thus if Lgt0 (1?)gt0 ,no ghosts, instabilities
or acausalities.
13
Conclusions
  • Effective gravity could
    help with the
  • cosmological constant problems

- Coincidence (Delayed) response to the
universe
becoming nonrelativistic - Fine tuning
Only Planck scale involved
- Simplest models feature a sudden future
singularity - Seems to have reasonable
LSS, could avoid ghosts and Solar system
constraints...
Whereas f(R) gravity does not help with the fine
tunings in the first place and in addition is
ruled out (or severely constrained) by ghosts,
LSS and Solar system.
About PowerShow.com