Modified Gravity vs. ?CDM

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Modified Gravity vs. ?CDM

• Roman Shcherbakov
• Astronomy 202b final presentation
• 12 December 2007

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?CDM
Dark parts should be illuminated /or/ eliminated
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Modified Newtonian Dynamics

• Proposed by Milgrom in 1983
• Heavily criticized thereafter

for agtgta0
Stronger gravity on large scales
for altlta0
Many modifications of these laws appeared later
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Other Modified Gravity Models

• SUper GRAvity (SUGRA) a candidate for the
  theory of
• 
  everything
• Modified Gravity Tensor/Vector/Scalar theory
• 
  by Moffat Bekenstein

• In contrast to MOND these theories
• Do not violate 3-d Newtons Law/conservation of
  momentum/ isotropy of space/Cosmological
  principle
• Have covariant description/equations are
  form-invariant
• Sometimes linear
• Have physical reasons to exist

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Tests on the scale of Solar system
Pioneer anomaly
Additional Solar-/Earth- ward acceleration for
both spacecrafts
Extreme relativistic pulsar PSR B191316
Keplers Law of planetary motion
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Tests on the scale of Galaxies
Flat rotation curves
Rotation curves in dwarf Galaxies may require
different fit parameters
Unusual shape and high velocities in Bullet
Cluster
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Tests on cosmological scale
Structure formation, no Silk damping
Relative height of first CMB peaks
Primordial nucleosynthesis
Accelerating expansion of the Universe?
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Conclusions

• People are not always critical about their work
  careful comparisons should
• be made
• Huge number of observational tests should be
  explained by alternative
• theories the circle of possible models is
  shrinking
• MOND violates isotropy of space, linearity,
  covariance and may not be used
• to fit any data
• General Relativity on the scale of Solar system
  Pioneer anomaly gt weak constrains on modified
  gravity models
• Flat rotation curves gt either dark matter /or/
  scale-dependent modification of gravity
• Structure formation gt presence of some dark
  matter component even for models with modified
  gravity
• Some modified gravity models (e.g. that by
  Moffat) may be as good as ?CDM model in sum over
  all the tests. Additional research/more tests are
  needed.

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Bibliography
Bekenstein J., Milgrom M. 1984, ApJ, 286,
7 Moffat, J. W. 2006, J. of Cosm. and Astropart.
Phys., 004 Moffat, J. W., \ Toth, V. T. 2007,
astro-ph/0710.0364v3 Brownstein, J. R., Moffat,
J.W. 2006, Class. Quantum Grav., 23,3427 Milgrom
M. 1983, ApJ, 270, 365 Milgrom M. 1983, ApJ, 270,
371 Scott D., Martin W., Cohn, J. D., Pierpaoli
E. 2001, astro-ph/0104435v1 Turyshev, S. G.,
Nieto, M. M., Anderson. J. D. 2005, gr-qc/0510081