1. Testing the Equivalence Principle for Dark Matter Using Tidal Streams Michael Kesden, CITA Collaborator: Marc Kamionkowski, Caltech COSMO ‘06 Tahoe City, CA Thursday, September 28, 2006

2. What is the Dark Matter?  Galactic rotation curves, large-scale structure (LSS), galaxy clusters all indicate Ω DM  0.25  Extensions to the Standard Model offer many possible WIMPs (axions, neutralinos, etc.)  Detection of non-gravitational interactions could help identify DM. What interactions might be observable?

3. Long-range DM interactions Perhaps DM interacts with DE Perhaps DM interacts with DE Log(   /m Pl 4 )  -120 « 1 Log(   /m Pl 4 )  -120 « 1   ~  m … Why now?   ~  m … Why now? Maybe acceleration due to scalar field, just like inflation. Scalar field should couple generically. Maybe acceleration due to scalar field, just like inflation. Scalar field should couple generically. String theory includes “dilatons”, light, neutral scalar fields that might interact with DM (Damour et al. 1990, Gubser & Peebles, 2004) String theory includes “dilatons”, light, neutral scalar fields that might interact with DM (Damour et al. 1990, Gubser & Peebles, 2004)

4. A “5th Force” for Dark Matter? Long-range DM force interpreted as violation of the equivalence principle (EP), the universality of free fall between stars and DM Long-range DM force interpreted as violation of the equivalence principle (EP), the universality of free fall between stars and DM Laboratory tests place tight limits on fifth force in visible sector (Su et al., 1994); no such limits for DM Laboratory tests place tight limits on fifth force in visible sector (Su et al., 1994); no such limits for DM Modeled by L int = g   V  = -g 2 /4  r exp{- m  r} (Frieman & Gradwohl, 1991) Modeled by L int = g   V  = -g 2 /4  r exp{- m  r} (Frieman & Gradwohl, 1991) Force suppressed by a factor  2  g 2 m Pl 2 /4  m  2 compared to gravity; how might we detect such a force? Force suppressed by a factor  2  g 2 m Pl 2 /4  m  2 compared to gravity; how might we detect such a force?

5. Cosmic Tests for 5th Force LSS LSS Attractive DM force enhances structure for (r < m  -1 ) (Gradwohl & Frieman, 1992) Attractive DM force enhances structure for (r < m  -1 ) (Gradwohl & Frieman, 1992) 5th force leads to scale-independent bias (Amendola & Tocchini-Valentini, 2002) 5th force leads to scale-independent bias (Amendola & Tocchini-Valentini, 2002) CMB CMB Models where coupled DE traces DM constrained by WMAP (Amendola & Quercellini, 2003) Models where coupled DE traces DM constrained by WMAP (Amendola & Quercellini, 2003) Clusters Clusters Baryons preferentially lost during mergers Baryons preferentially lost during mergers Is there new test with different systematics, greater sensitivity? Is there new test with different systematics, greater sensitivity?

6. Tidal Disruptions Galaxies form hierarchically; dwarf galaxies in Local Group continue to merge with Milky Way Galaxies form hierarchically; dwarf galaxies in Local Group continue to merge with Milky Way Smaller galaxies tidally disrupted by larger hosts at distances R where: Smaller galaxies tidally disrupted by larger hosts at distances R where: r sat > r tid ~ R(m sat /2M R ) 1/3 Tidal disruption establishes energy scales: Tidal disruption establishes energy scales: E sat » E tid » E bin  disrupted stars retain similar orbits to satellite; trail/lead with gain/loss in energy E sat » E tid » E bin  disrupted stars retain similar orbits to satellite; trail/lead with gain/loss in energy

7. Tidal-stream Asymmetry Non-uniformity of Galactic gradient leads to natural asymmetry: Non-uniformity of Galactic gradient leads to natural asymmetry:   DM force displaces stars from bottom of satellite’s potential well, a new DM-induced asymmetry DM force displaces stars from bottom of satellite’s potential well, a new DM-induced asymmetry  DM asymmetry exceeds natural asymmetry when: DM asymmetry exceeds natural asymmetry when:

8. Sagittarius Dwarf Spheroidal Sgr dwarf is closest satellite at 24 kpc Sgr dwarf is closest satellite at 24 kpc Stellar stream observed by 2MASS using M- giants with known age, color-magnitude relation Stellar stream observed by 2MASS using M- giants with known age, color-magnitude relation Surface densities, radial velocities, distances well-measured for Surface densities, radial velocities, distances well-measured for leading: -100º <  < -30º trailing: 25º <  < 90º trailing: 25º <  < 90º (Law, Johnston, & Majewski, 2005) Stellar densities also measured by SDSS (Belokurov et al., 2006) Stellar densities also measured by SDSS (Belokurov et al., 2006)

9. Simulations N-body simulation of satellite galaxy with: N-body simulation of satellite galaxy with: M = 5  10 8 M , M/L = 40 M  /L  M = 5  10 8 M , M/L = 40 M  /L  Pericenter = 14 kpc, Apocenter = 59 kpc Pericenter = 14 kpc, Apocenter = 59 kpc Initial conditions generated by GALACTICS (Widrow & Dubinski, 2005) Initial conditions generated by GALACTICS (Widrow & Dubinski, 2005) Simulations evolved using GADGET-2 (Springel, 2005) Simulations evolved using GADGET-2 (Springel, 2005)

10. Stellar Streams of Sgr Dwarf

11. Tidal Streams Probe “Fifth” Force

12. Satellite Mass

13. Satellite Spin

14. Satellite Orbit

15. Galactic Model

16. Stellar density profile

17. Mass-to-Light Ratio

18. Leading-to-Trailing Stream Ratios Attractive force suppresses leading- to-trailing ratio Attractive force suppresses leading- to-trailing ratio CurveColor Standardblack Satellite Massmagenta Satellite Spinred Circular Orbittop blue Planar orbitbottom blue Heavy diskcyan Two profilesgreen Lower M/Lyellow

19. Conclusions We don’t know what the DM is. Theory suggests we consider the possibility of a long-range “fifth force”. We don’t know what the DM is. Theory suggests we consider the possibility of a long-range “fifth force”. Tidally disrupting galaxies ideal test; core DM-dominated but not streams Tidally disrupting galaxies ideal test; core DM-dominated but not streams Attractive DM-force sweeps core ahead. Disrupted stars preferentially gain energy; LTR suppressed. Attractive DM-force sweeps core ahead. Disrupted stars preferentially gain energy; LTR suppressed. Tidal streams are a messy probe of new physics, but the signature of a DM force is very distinctive, model- independent. Tidal streams are a messy probe of new physics, but the signature of a DM force is very distinctive, model- independent. The Sgr tidal stream is well observed; new tidal streams have been discovered in last few months in SDSS. Future surveys like SIM or Gaia will find even more. The Sgr tidal stream is well observed; new tidal streams have been discovered in last few months in SDSS. Future surveys like SIM or Gaia will find even more. Like dropping stars and DM off Leaning Tower of Pisa! Like dropping stars and DM off Leaning Tower of Pisa!