Download - Self- interacting Dark Matter 2.0:
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.