Modified Gravity vs. Modified Gravity vs. ΛΛCDMCDM

Roman ShcherbakovRoman Shcherbakov

Astronomy 202b final presentationAstronomy 202b final presentation

12 December 200712 December 2007

“Dark” parts should be illuminated /or/ eliminated

ΛΛCDM CDM

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