Modified Gravity vs. ΛCDM Roman Shcherbakov Astronomy 202b final presentation 12 December 2007

“Dark” parts should be illuminated /or/ eliminated ΛCDM

Modified Newtonian Dynamics Proposed by Milgrom in 1983 Heavily criticized thereafter – acceleration scale for a>>a 0 for a<<a 0 Many modifications of these laws appeared later “Stronger gravity” on large scales

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: 1.Do not violate 3-d Newton’s Law/conservation of momentum/ isotropy of space/Cosmological principle 2.Have covariant description/equations are form-invariant 3.Sometimes linear 4.Have physical reasons to exist

Tests on the scale of Solar system Pioneer anomaly Kepler’s Law of planetary motion motion Additional Solar-/Earth- ward acceleration for both spacecrafts Extreme relativistic pulsar PSR B

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

Tests on cosmological scale Structure formation, no Silk damping Relative height of first CMB peaks Primordial nucleosynthesis Accelerating expansion of the Universe?

Conclusions People are not always critical about their work – careful comparisons should be made be made Huge number of observational tests should be explained by alternative theories: the circle of possible models is shrinking theories: the circle of possible models is shrinking MOND violates isotropy of space, linearity, covariance and may not be used to fit any data to fit any data General Relativity on the scale of Solar system + Pioneer anomaly => weak constrains on modified gravity models Flat rotation curves => either dark matter /or/ scale-dependent modification of gravity Structure formation => 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 ΛCDM model in sum over all the tests. Additional research/more tests are needed.

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