Modified Gravity vs. Modified Gravity vs. ΛΛCDMCDM
Roman ShcherbakovRoman Shcherbakov
Astronomy 202b final presentationAstronomy 202b final presentation
12 December 200712 December 2007
Modified Newtonian DynamicsModified Newtonian Dynamics
• Proposed by Milgrom in 1983• Heavily criticized thereafter
– acceleration scale
for a>>a0
for a<<a0
Many modifications of these laws appeared later
“Stronger gravity” on large scales
Other Modified Gravity ModelsOther 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:1. Do not violate 3-d Newton’s Law/conservation of
momentum/ isotropy of space/Cosmological principle2. Have covariant description/equations are form-invariant3. Sometimes linear4. Have physical reasons to exist
Tests on the scale of Solar systemTests on the scale of Solar systemPioneer anomalyPioneer anomaly
Kepler’s LawKepler’s Lawof planetaryof planetary motionmotion
Additional Solar-/Earth- ward acceleration for both spacecrafts
Extreme relativistic pulsar PSR B1913+16
Tests on the sTests on the scale of Galaxiescale of GalaxiesFlat rotation curves
Rotation curves in dwarf Galaxies may require different fit parameters
Unusual shape and high velocities
in Bullet Cluster
Tests on cosmological scaleTests on cosmological scaleStructure formation, no Silk damping
Relative height of first CMB peaks
Primordialnucleosynthesis Accelerating expansion of the Universe?
ConclusionsConclusionsPeople are not always critical about their work – careful comparisons should People are not always critical about their work – careful comparisons should
be madebe made
Huge number of observational tests should be explained by alternativeHuge number of observational tests should be explained by alternative
theories: the circle of possible models is shrinkingtheories: the circle of possible models is shrinking
MOND violates isotropy of space, linearity, covariance and may not be usedMOND violates isotropy of space, linearity, covariance and may not be used
to fit any datato fit any data
General Relativity on the scale of Solar system + Pioneer anomaly => weak General Relativity on the scale of Solar system + Pioneer anomaly => weak constrains on modified gravity modelsconstrains on modified gravity models
Flat rotation curves => either dark matter /or/ scale-dependent modification Flat rotation curves => either dark matter /or/ scale-dependent modification of gravityof gravity
Structure formation => presence of some dark matter component even for Structure formation => presence of some dark matter component even for models with modified gravitymodels with modified gravity
Some modified gravity models (e.g. that by Moffat) may be as good as Some modified gravity models (e.g. that by Moffat) may be as good as ΛΛCDM model in sum over all the tests. Additional research/more tests are CDM model in sum over all the tests. Additional research/more tests are needed.needed.
BibliographyBibliography
Bekenstein J., Milgrom M. 1984, ApJ, 286, 7Moffat, J. W. 2006, J. of Cosm. and Astropart. Phys., 004Moffat, J. W., \& Toth, V. T. 2007, astro-ph/0710.0364v3Brownstein, J. R., Moffat, J.W. 2006, Class. Quantum Grav., 23,3427Milgrom M. 1983, ApJ, 270, 365Milgrom M. 1983, ApJ, 270, 371Scott D., Martin W., Cohn, J. D., Pierpaoli E. 2001, astro-ph/0104435v1Turyshev, S. G., Nieto, M. M., Anderson. J. D. 2005, gr-qc/0510081
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