THE CASE FOR MODIFIED GRAVITY

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THE CASE FOR MODIFIED GRAVITY

• James Binney
• Oxford University

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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)

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NGC 3198
Begeman (1987)
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Modifying gravity

• Modify Newtonian theory
  at large distances?
  or at low accelerations?

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Adding a0
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BekensteinMilgrom Eq.
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Tully-Fisher

• Deep MOND regime when µ(x)x
• At large r always enter deep MOND

Sanders Verheijen
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Fits to vc(r) for both LSB HSB Galaxies
(Sanders McGaugh 02) a01.2 10-8 cm s-2
a0H0c/2p ?3(a0/c)2
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U Maj Sanders Verheijen
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Recover predicted M/L values
Data Sanders Verheijen Models Bell de Jong
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Giant E galaxies
Data Romanowsky et al 03 Models Milgrom
Sanders 03 Solid isotropic
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Clusters of Galaxies
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dSph galaxies
? Fi/Ft
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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 F obtained with spatially const M/L
  quasi-isothermal DM halo
• Fit M/L, ?bar, ?spiral
• M/L for stars set by dynamics of non-axisymmetric
  structure
• DM halo makes up balance for tangent-velocity
  curve

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Bissantz Englmaier Gerhard
CO observed
simulated
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m2 x 1.5
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Bissantz Englmaier Gerhard (03)

• Find ?bar 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 a10.7 kpc added
• With ?(x)x/(1x) KhN/KhM0.950.15
  (Famaey B 04)

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Microlensing
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Optical depths
Bissantz Gerhard (02)
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Bissantz Debattista Gerhard (04)

• Use novel N-body technique to find dynamical
  model that reproduces Bissantz Gerhard
  photometry
• Adopt M/L, ? normalization from BEG
• No free parameters in F
• Reproduce proper motions of bulge stars in
  Baades window etc
• For plausible mass function of stars, reproduce
  MACHO microlensing event duration distribution

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(MLlt,MLgt)(.04,10) or (.075,10)

• Conclusion stars-only MW gives good fits to both
  optical depth duration distribution

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Klypin et al (02)

• ?CDM models of MW
• Adiabatic compression optional L exchange

No L exchange
L exchange
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TeVeS

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

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

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• 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 F fields in
  TeVeS

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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