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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/0610298. Long Range Interaction of ~Gravitational Strength is Generic!.
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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/0610298
Long Range Interaction of ~Gravitational Strength is Generic! V(r ) = VN (r ) exp(-r/r5) • 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. • ~ (MPl / vev)2and vev’s are naturally of order MGUT or MPl => gravitational strength coupling. • May be Yukawa with r 5 ~ m-1 or r 5 ~ a (GF+Peebles astro-ph/0307316) • May have more complicated dependence on distance, e.g., Chameleon models. => must test for fifth force on all scales.
IE0657-56 “bullet cluster” Markevitch astro-ph/0511345 Z = 0.3 Mach 3.0 ± 0.4 vgas = 4740 ± 630 km/s (actually, - 550 km/s) Tclus = 14 keV (Tif quiescent ~ 10 keV)
NEW -- IE 0657-56 in 2006Weak + Strong Lensing Surface Density (red)X-ray Brightness (white) From Bradac et al astro-ph/0608408 DM proof: Clowe et al, astro-ph/0608
Lensing => • Main cluster: • M200 = 1.5 1015 Msun • V200 = 1740 km/s • Sub cluster: • M200 = 1.5 1014 Msun
Furthermore… • Sub-cluster is moving in plane of sky (<~8o). • 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 = 4740 +670- 550 km/s • If Keplerian, vplunging = 21/2 vcirc = 3360 km/s • How serious is this > 2 “discrepancy”?
More careful modelingGRF + Rachel Rosen, astro-ph/0610298 • 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
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 withRosat: Increases predicted velocity by ~10 km/s
Hayashi and WhiteMNRAS 370, L38 (2006) and GRF+RAR update • HW: Parameterize distribution of vsubcl/v200 in Millenium Run. • HW: using old (and rounded) values of vsubcl and v200 find 1/500 chance of finding subcluster as fast as bullet. • FR: Same analysis but updating vsubcl and v200 => find probability = 0.8 10-7. • FR: With vsubcl = 4190 km/s, find probability = 10-3.
Some Observational Benefits of a 5th ForceLarge scale, high precision simulations underway (GRF, V. Springel) • Helps reconcile 8 from WMAP (.75) and Large Scale Structure simulations (0.9-1.1) • 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 • Reducesbaryonic 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/0412586: static case, rough statistics.
Sagittarius Tidal Streams --evidence for or against 5th force? Majewski et al. ApJ 599:1082, 2003 (2MASS M-Stars, ages ≤ 2 Gyr • 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 Law, Johnston, Majewski ApJ 619:807, 2005
Conclusions • Interpreting IE 0657-56 at face value as “5th” force: • r5 1 Mpc ~ 0.2 - 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 • IfDM experiences a 5th force, loop corrections + EotWash => DM will be hard (impossible?) to see in direct detection expts