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 astro-ph/

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.  ~ ( M Pl / vev) 2 and vev’s are naturally of order M GUT or M Pl => gravitational strength coupling. May be Yukawa with r 5 ~ m  -1 or r 5 ~ a ( GF+Peebles astro- ph/ ) 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 )

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

IE in 2004

NEW -- IE in 2006 Weak + Strong Lensing Surface Density (red) X-ray Brightness (white) From Bradac et al astro-ph/ DM proof: Clowe et al, astro-ph/0608

Lensing => Main cluster: –M 200 = M sun –V 200 = 1740 km/s Sub cluster: –M 200 = M sun

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

More careful modeling GRF + Rachel Rosen, astro-ph/ 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 Observed: v = 4740 km/s; v -1  = 4190 km/s “Conspiracy model” predicts v = 3435 km/sec

Predictions with Gravity Alone

Atypical Mass Accretion History? Results with actual Mass Accretion History of 12 most massive halos in M. White simulation Compare to Wechsler et al formula (red curve) Most extreme case has 10% bigger velocity than given by mean MAH

Other Uncertainties Weak Lensing -- Mass along line-of-sight : Decreases predicted velocity Interpretation of X-ray data --Trajectory not exactly in plane of sky: Increases observed velocity Dynamical Calculation -- Trajectory not exactly through center of cluster: more dynamical friction => Decreases predicted velocity Unseen Mass -- Add maximum consistent with Rosat: Increases predicted velocity by ~10 km/s

Hayashi and White MNRAS 370, L38 (2006) and GRF+RAR update HW: Parameterize distribution of v subcl /v 200 in Millenium Run. HW: using old (and rounded) values of v subcl and v 200 find 1/500 chance of finding subcluster as fast as bullet. FR: Same analysis but updating v subcl and v 200 => find probability = FR: With v subcl = 4190 km/s, find probability =

Some Observational Benefits of a 5th Force Large scale, high precision simulations underway (GRF, V. Springel) Helps reconcile  8 from WMAP (.75) and Large Scale Structure simulations ( ) 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 Reduces baryonic fraction in clusters. Helps empty voids; reduces late accretion –GRF-Peebles qualitative argument: voids emptier, less late accretion –Confirmed by Nusser, Gubser, Peebles simulation astro-ph/ : static case, rough statistics.

Sagittarius Tidal Streams -- evidence for or against 5th force? Law, Johnston, Majewski ApJ 619:807, 2005 Law, Johnston, Majewski: Precession of orbital plane: Oblate Halo L.o.s. velocities: Prolate Halo Kesden Kamionkowski: Symmetric tails (?) constrain  to be small GRF: Prolate-oblate contradiction can be solved by  > 0 -- GF, KJ, PJEP in progress Majewski et al. ApJ 599:1082, 2003 (2MASS M-Stars, ages ≤ 2 Gyr

Conclusions Interpreting IE at face value as “5th” force: –r 5  1 Mpc  ~ –Consistent with present constraints (Gradwohl&Frieman, ApJ 398, 1992) Improving IE 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 r 5 accessible via Tidal Tails of dwarf galaxies in Milky Way. Kesden&Kamionkowski 2006 If DM experiences a 5th force, loop corrections + EotWash => DM will be hard (impossible?) to see in direct detection expts