1. Evidence for a Long-Range Dark Matter Self Interaction (“Fifth Force”) Glennys R. Farrar Center for Cosmology and Particle Physics New York University See GRF + Rachel Rosen, preprint in preparation

2. Long Range Interaction of ~Gravitational Strength is Generic! String theory and most extensions of the SM contain fields, e.g., moduli, which are massless at every order of perturbation theory => very long range. Vevs are naturally of order M GUT or M Pl => very weak coupling.  ~ ( M Pl / vev) 2 May be Yukawa with r 5 ~ m -1 or r 5 ~ a ( GF+Peebles ) May have more complicated dependence on distance, e.g., Chameleon models. => must test for fifth force on all scales. V(r ) =  V N (r ) exp (-r/r 5 )

3. IE 0657-67 “bullet cluster” Markevitch astro-ph/0511345 Z = 0.3 Mach 3.0 ± 0.4 v gas = 4740 ± 630 km/s (actually, - 550 km/s) T clus = 14 keV (T if quiescent ~ 10 keV)

4. IE 0657-56 in 2004

5. NEW Weak + Strong Lensing Surface Density (red) X-ray Brightness (white) From Bradac et al astro-ph/0608408 DM proof: Clowe et al, astro-ph/0608

6. Furthermore… Sub-cluster is moving in plane of sky (<~8 o ). Sub-cluster is on its first pass; went directly through center of main cluster. Gas bullet lags DM. (model-independent disproof of MOND) DM sub-cluster velocity = 4740 +670 - 550 km/s If Keplerian, v plunging = 2 1/2 v circ = 3360 km/s How serious is this > 2  “discrepancy”?

7. More careful modeling GRF + Rachel Rosen, paper in preparation Consider various density profiles for main DM cluster. Use Mass Accretion History of Wechsler et al (2002) Use actual MAH of 12 most massive simulated clusters Fix initial infall velocity to 300 km/s (600 km/s) => initial position and time are not independent. Predicted final velocity is insensitive to starting time. “Fiducial model” predicts v = 2950 km/sec Results range from 2360 km/s to ~ 3500 km/s. Best for no-5th force: prolate mass distsribution with c/a = 0.65, aligned with direction of motion => v <~3500 km/sec Observed: v = 4740 km/s; v -1  = 4190 km/s

8. MAH variations and other complications in modeling Use actual Mass accretion history of 12 most massive halos in M. White& J. Cohn simulation, compared to WBPKD formula –Most extreme case has 10% bigger velocity Other complications either increase discrepancy (shape of DM distribution, weak lensing bkg, …) or appear to be small Statistical Appoach. E. Hayashida & S. White, astro-ph/0604443 -- used old and rounded parameter values. Updating their analysis with newest v sub and accurate mass values, gives –Prob( v sub /V 200 > obs) < 10 -6 –Prob(v -1sigma /V 200 > obs < 10 -3

9. Some Observational Benefits of a 5th Force Helps reconcile  8 from WMAP (.75) and Large Scale Structure simulations (0.9-1.1) –Large scale, high precision simulations underway (GRF, V. Springel) Helps explain factor-10 discrepancy between LCDM simulations and number of superclusters observed in SDSS (Einasto et al, astro-ph/06…) Helps explain insufficiency of observed DM substructures in galaxies Helps empty voids (?); reduces late accretion –(Nusser et al astro-ph/0412586: static case, rough statistics. GRF-Peebles qualitative argument, voids emptier, less late accretion)

10. Conclusions Interpreting IE 0657-56 at face value as “5th” force: –r 5  1 Mpc  ~ 1/2 - 1 –Consistent with present constraints (Gradwohl&Frieman, ApJ 398, 1992) Improving IE 0657-56 measurements: –Improve lensing: measure redshifts of more arcs –Model gas deceleration; reduce error on gas bullet velocity Need large statistics studies in other systems (edges of voids, velocity dispersion vs weak lensing, …) SDSS…. Smaller r5 accessible via Tidal Tails of dwarf galaxies in Milky Way. Kesden&Kamionkowski 2006 If DM experiences a 5th force, it may be hard to see in direct detection expts (loop corrections + EotWash)