# Presentation: 408280

## 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!

- 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)2 and 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.

*V(r ) = **** V**N** (r ) ** exp**(-r/r**5**)*

## 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)

## IE 0657-56  in 2004 

- IE 0657-56  in 2004

## NEW -- IE 0657-56  in 2006 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**

## 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 modelingGRF + 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**

## 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 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 Force Large 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
- 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/0412586: 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 0657-56 at face value as “5th” force:
**r****5**** ******** 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
- If DM experiences a 5th force, loop corrections + EotWash => DM will be hard (impossible?) to see in direct detection expts