Long%20distance%20modifications%20of%20gravity%20in%20four%20dimensions.

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Long distance modifications of gravity in four
dimensions.
Karel Van Acoleyen Durham University, IPPP

• Work done in collaboration with Ignacio Navarro.
• gr-qc/0506096 (Phys. Lett. B 622, 2005)
• gr-qc/0511045 (JCAP 03, 2006 )
• gr-qc/0512109
• In preparation

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The models
with
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Prime motivation alternatives for Dark Energy

• With crossover scale

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Propagating degrees of freedom
(on deSitter
space)

• massless spin 2 graviton
• extra massive scalar
• no ghosts
  

Effective Planck mass and the mass of the scalar
depend on the background !!
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Schwarzschild solution at large distances

• On vacuum, the mass of the scalar is very light.
• problem for the Solar
  System tests?

BUT, the perturbation series breaks down at
short distances Corrections go like
with
This distance is huge 10 kpc for the Sun,
1 Mpc for the Milky Way )
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Schwarzschild solution at short distances

• The curvature in the Solar System is huge. So we
  dont expect much modification. (We need Q!)
• What about the extra scalar? Corrections for
• Mass depends on the background
• 
  
• Explicitly

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To summarize
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Could the non-perturbative region play the role
of the dark matter halo?

• Yes! (maybe) in the limit n 0
• ? Logarithmic actions

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Logarithmic actions as an alternative to Dark
Energy and Dark Matter halos?

• For a large class of models there is an
  enhancement of Newtons constant at large
  distances at large distances there seems
  to be more matter than there actually is .
• Typically, there exist deSitter attractors, with
  the Hubble constant of the order of the crossover
  scale.
• Departure from Newtonian gravity, at a critical
  acceleration set by the same crossover scale.
• MOND?

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Logarithmic actions testable predictions on
Earth!

• Mass of the scalar on earth
• short distance corrections at
  0.1mm.
• Explicit calculation gives an anisotropic
  correction, for the potential of a probe
• mass in the background field of the earth

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Conclusions

• One can consistently modify gravity at large
  distances in 4D.
• The modification is characterized by
• 1. an extra scalar degree of freedom,
  with a mass that runs with the backgroundcurvature
  ( )
• 2. a running Newtons constant
• Logarithmic actions have potential to unify the
  DE and DM problem
• And give testable predictions on Earth.

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Lots of stuff to do

• Examine the influence on the CMB of the extra
  scalar running Newtons ConstantLorentz
  violation.
• Understand the Lorentz violation theoretically
  
• consistent?
• Solve in the non-perturbative intermediate regime
  
• MOND?
• .