Self-interacting

Dark Matter 2.0:

Annika PeterMcCue Fellow

uC irvine

Back and Better Than Ever!

M. Rocha, AP+ 1204.XXXXAP+ 1204.XXXX

The Universe as a cupcake

Dark energy: ~72%

Dark matter: ~23%

Baryons: ~4%

???

Image credits: NASA/JPL; NASA, Jeff Hester, and Paul Scowen (Arizona State University); NASA, ESA, S. Beckwith (STScI), and the HUDF team

The cold dark matter orthodoxy

• “Born cold”.• Late-time behavior: collisionless and boring.

r

over

dens

ity

Millennium simulation

Image credits: M. Blanton and the SDSS

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)

MS 2137-23Sand et al. 2008

Tightest constraint by far (by > 10x)!

Requires a non-circularly-symmetric surface density at r > 70 kpc.

Assume ε=0 if .

σ/m < 0.02 cm2/g.

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

1015 Mclusters

Milky Way

Dwarfgalaxies

Milky Waydwarfs~hundred pc

~kpc

Observations

Dwarf core problem(Kuzio de Naray et al. 2008)

“Too big to fail”Milky Way dwarfs(Boylan-Kolchin et al. 2011)

Galaxy cluster densitiesρ ~ 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!

1015 Mclusters

Milky Way

Dwarfgalaxies

Milky Waydwarfs~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.