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THE CASE FOR MODIFIED GRAVITY

THE CASE FOR MODIFIED GRAVITY. James Binney Oxford University. Outline. MOND as a replacement for DM (Sanders & McGaugh 02) Absence of DM interior to the Sun (Bissantz et al 03, 04) TeVeS Lorentz-covariant MOND (Bekenstein 2004). NGC 3198. Begeman (1987).

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THE CASE FOR MODIFIED GRAVITY

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  1. THE CASE FOR MODIFIED GRAVITY James Binney Oxford University

  2. Outline • MOND as a replacement for DM (Sanders & McGaugh 02) • Absence of DM interior to the Sun (Bissantz et al 03, 04) • TeVeS Lorentz-covariant MOND (Bekenstein 2004)

  3. NGC 3198 Begeman (1987)

  4. Modifying gravity • Modify Newtonian theory at large distances? or at low accelerations?

  5. Adding a0

  6. Bekenstein—Milgrom Eq.

  7. Deep MOND regime – when µ(x)~x At large r always enter deep MOND Tully-Fisher Sanders & Verheijen

  8. Fits to vc(r) for both LSB & HSB Galaxies (Sanders & McGaugh 02) a0=1.2 10-8 cm s-2 a0~H0c/2π; Λ~3(a0/c)2

  9. U Maj Sanders & Verheijen

  10. Recover predicted M/L values Data: Sanders & Verheijen Models: Bell & de Jong 01

  11. Giant E galaxies Data: Romanowsky et al 03 Models: Milgrom & Sanders 03 Solid: isotropic

  12. Clusters of Galaxies

  13. dSph galaxies η = Fi/Ft

  14. DM in the MW? • Bissantz & Gerhard (02) Determine near-IR luminosity density from COBE K & L photometry • Advances previous work by including spiral structure in disk • Bissantz Englmaier & Gerhard (03) study gas flow in Φ obtained with spatially const M/L + quasi-isothermal DM halo • Fit M/L, ωbar, ωspiral • M/L for stars set by dynamics of non-axisymmetric structure • DM halo makes up balance for tangent-velocity curve

  15. Bissantz Englmaier & Gerhard CO observed simulated

  16. m=2 x 1.5

  17. Bissantz Englmaier & Gerhard (03) • Find ωbar in good agreement solar nhd kinematics • With 4 arms get good pattern of ridge lines • Vc near sun ~35 km/s below true value unless DM halo with a=10.7 kpc added • With (x)=x/(1+x) KhN/KhM=0.95§0.15 (Famaey & B 04)

  18. Microlensing

  19. Optical depths Bissantz & Gerhard (02)

  20. Bissantz Debattista & Gerhard (04) • Use novel N-body technique to find dynamical model that reproduces Bissantz & Gerhard photometry • Adopt M/L, ω normalization from BEG • No free parameters in Φ • Reproduce proper motions of bulge stars in Baade’s window etc • For plausible mass function of stars, reproduce MACHO microlensing event duration distribution

  21. Conclusion: stars-only MW gives good fits to both optical depth & duration distribution (ML<,ML>)=(.04,10) or (.075,10)

  22. Klypin et al (02) • ΛCDM models of MW • Adiabatic compression & optional L exchange No L exchange L exchange

  23. TeVeS • Bekenstein (04) presents Lorentz-covariant theory (TeVeS) that reduces to MOND in appropriate limit

  24. Standard cosmologies • Grav. Lensing as if DM present • No superluminal modes

  25. TeVeS important development Link to effective field theory? • Can now extend MOND to CMB and large-scale structure • If not worse than CDM in these fields, must be favoured theory • Then question: significance of Uµ and Φ fields in TeVeS

  26. Conclusions • MOND has amazing ability to model data taken after it was invented • Excellent fits to galaxy rotation curves require M/L(colour) as from SS theory • Compelling evidence that negligible DM interior to Sun • Now limiting form of Lorentz covariant theory • MOND really might be the next great step in physics

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