Self- interacting Dark Matter 2.0: Back and Better Than Ever! Annika Peter McCue Fellow uC irvine M. Rocha, AP+ 1204.XXXX AP+ 1204.XXXX

The Universe as a cupcake Baryons: ~4% Image credits: NASA/JPL; NASA, Jeff Hester, and Paul Scowen (Arizona State University); NASA, ESA, S. Beckwith (STScI), and the HUDF team Dark matter: ~23% Dark energy: ~72% ???

The cold dark matter orthodoxy “Born cold”. Late-time behavior: collisionless and boring. Image credits: M. Blanton and the SDSS r overdensity Millennium simulation

Small-scale issues (circa 2000) Dwarf core problem (Kuzio de Naray et al. 2008) Missing satellites problem (Moore et al., Klypin et al. 1999)

Self-interacting dark matter (SIDM) Elastic scattering---need cross section ~1 cm2/g (>1012 times stronger than weak force) to be interesting. Original formulation (Spergel & Steinhardt 2000): hard-sphere elastic scattering. In vogue now: on particle side (hidden-sector models, Sommerfeld-enhanced dark matter)---generally velocity-dependent.

Phenomenology Looks exactly like CDM on large scales: 10 Mpc/h slice, CDM 10 Mpc/h slice, σ/m = 1 cm2 /g

Phenomenology Generic predictions when : Rounder halo in inner parts. Cored (less dense) halo density profiles. Fewer satellites close to the center. CDM SIDM

Version 1.0 nail in the coffin Miralda-Escude (2002) Requires a non-circularly-symmetric surface density at r > 70 kpc. Assume ε=0 if .  σ/m < 0.02 cm2/g. MS 2137-23 Sand et al. 2008 Tightest constraint by far (by > 10x)!

The problem with shapes We see surface density (or gravitational potentials) in projection. If inner parts have flattened density, outer parts have even greater weight. σ/m=1 cm2/g CDM

SIDM 2.0: It’s back! σ/m=1 cm2/g allowed!

Density profile

Cores Milky Way dwarfs Milky Way 1015 M clusters Dwarf galaxies ~hundred pc ~kpc

Observations Galaxy cluster densities “Too big to fail” Dwarf core problem (Kuzio de Naray et al. 2008) “Too big to fail” Milky Way dwarfs (Boylan-Kolchin et al. 2011) Galaxy cluster densities ρ ~ r-β Richard Ellis and co. (Newman et al. 2011) Need less DM in ~100 pc in 109-1010 M halos Need cores in ~1 kpc in 1011 M halos Need cores in ~100 kpc in 1015 M halos

Cores! Milky Way dwarfs Milky Way 1015 M clusters Dwarf galaxies ~hundred pc ~kpc

Subhalos

Takeaway points “Vanilla” SIDM is far from dead! Moreover, clinging to one particular unproven model (cough, cough, CDM) may be dangerous. Try to constrain general phenomenology! With at least a modicum of rigor! A reanalysis of the old constraints shows σ/m=1 cm2/g OK! (AKA, do not believe everything you read) Suggestive core sizes! Cross sections that give interesting-sized cores do NOT substantially reduce subhalo mass function. Clusters remain an interesting environment for constraints.