Dark Matter and Structure Formation Hai-Bo Yu University of - - PowerPoint PPT Presentation

Dark Matter and Structure Formation

Hai-Bo Yu University of California, Riverside

September 10, 2019

TAUP , 2019 TOYAMA, JAPAN

Dark Matter

27%

5%

68%

Dark Matter Halos: Hosting Galaxies

Aquarius Project, Springel+(2008)

Dark matter is the key for understanding structure formation of the universe

Dark Matter Properties

Dark Stable Cold X

None of the standard model particles can be a dark matter candidate

DM candidates: WIMPs, Axions…

See Hitoshi Murayama’s talk

⽩百居易《⻓門恨歌》

“上穷碧落下⻩黅泉，两处茫茫皆不⻅观。”

WIMP/DM Search Status

He exhausted all avenues in heaven and the nether world, Boundless and vast as they were, he could not bring her existence to light.

A Song of Immortal Regret, Bai Juyi (772-846)

A Critical Rethinking

• Why do we think dark matter interacts with the standard model

particles, aside from gravity?

• What if dark matter does not interact with us? nightmare scenario?
• How can we learn about the particle nature of dark matter from

astrophysical observations?

Cold Dark Matter

• Large scales: very well
• Small scales (dwarf galaxies, sub-halos, galaxy clusters)
• Core vs cusp
• Diversity
• Too Big To Fail
• Cores in galaxy clusters
• Ultra diffuse galaxies…

Universal Density Profile

ρs r/rs(1 + r/rs)2

Aquarius Project, Springel+ (2008) Navarro-Frenk-White (NFW) profile (1996)

CDM-only cosmological simulations

∼ 1 r ∼ 1 r3

∼ 1 r2

Core vs Cusp Problem

• DM-dominated systems (dwarfs, LSBs)

∼ ρsrs/r

∼ ρ0

ρs r/rs(1 + r/rs)2

Flores & Primack (1994); Moore (1994); de Blok & McGaugh (1997)…

mass-to-light ratio

NFW (1996) Tulin & HBY (2017)

Diversity Problem

Oman+(2015)

All galaxies have the same

• bserved

Vmax!

Colored bands: hydrodynamical simulations of CDM (weak feedback)

Reproduced from the data compiled in Oman+(2015)

Vcirc(2kpc) has a factor of ~4 scatter for fixed Vmax

A Big Challenge to CDM

Mhalo~109-1012 M☉

core cusp

The diversity is expected if dark matter has strong self-interactions

Self-Interacting Dark Matter

• Self-interactions thermalize the inner halo

Γ ' nσv = (ρ/mX)σv ⇠ H0

σ/mX ~1 cm2/g (nuclear scale)

CDM SIDM

MW-like halo σ/mX =2 cm2/g

From Ran Huo

CDM SIDM

DM Heat Isothermal distribution Review: Tulin & HBY (Physics Reports 2017)

Addressing the Diversity Problem

• DM self-interactions thermalize the inner halo

DM-dominated galaxies: Lower the central density and the circular velocity

ρX ∼ e−Φtot/σ2

0 ∼ e−ΦX/σ2

Isothermal distribution

Vmax=70 km/s

CDM SIDM only

2 4 6 8 10 20 40 60 80 Radius (kpc) Vcir (km/s)

2σ range of concentration

σ/m=3 cm2/g

with Kamada, Kaplinghat, Pace (PRL 2017)

High Surface Brightness Galaxies

• DM self-interactions tie DM together with baryons

Thermalization leads to higher DM density due to the baryonic influence

Increasing baryon concentration

ρX ∼ e−Φtot/σ2

0 ∼ e−ΦB/σ2

Vmax=120 km/s, MD=1010M⊙ CDM SIDM,RD=2 SIDM,RD=3 SIDM,RD=6 SIDM only

0.1 0.5 1 5 10 50 100 105 106 107 108 109 Radius (kpc) Density (MSun/kpc3)

with Kamada, Kaplinghat, Pace (PRL 2017) with Kaplinghat, Keeley, Linden (PRL 2014) with Kaplinghat, Linden (PRL 2015)

• Intrinsic scatter in halo concentration
• Diverse baryon distributions
• SIDM thermalization ties DM and baryon distributions in the RIGHT way

2 4 6 8 10 12 14 20 40 60 80 100

[] [/]

UGC05764 UGC07603 IC2574 NGC1705 UGC07151 UGC08490 UGC05750 UGC05721

low concentration low surface brightness high concentration high surface brightness σ/m=3 cm2/g

with Kamada, Kaplinghat, Pace (PRL 2017) with Creasey, Sameie, Sales+ (MNRAS 2017)

30 galaxies σ/m=3 cm2/g

With Ren, Kwa, Kaplinghat (PRX, 2018)

We fitted 147 galaxies (3.6 μm band)!

A Much Larger Sample

the SPARC sample, Lelli, McGaugh, Schombert (2016)

CDM w/Strong Feedback vs SIDM

Gray lines: NIHAO simulations of CDM (3σ band)

Solid lines: SIDM fits

Santos-Santos+(2017)

“strong/violent” feedback

[] [/]

(~2σ in the c200-M200 relation)

With Ren, Kaplinghat (to appear)

SIDM does better than any other model in the literature

Model Comparison

With Ren, Kaplinghat (to appear) Red: CDM with strong feedback

Valli & HBY (Nature Astronomy 2018)

Beyond Field Galaxies

Milky Way Satellite Galaxies

with Sameie, Sales+ (2019) Kaplinghat, Valli, HBY (2019)

Dark matter self-interactions+Tidal interactions σ/m=3 cm2/g

See also: Kahlhoefer+ (2019), Nishikawa+ (2019)

SIDM from Dwarfs to Clusters

With Kaplinghat, Tulin (PRL, 2015)

Galaxies: Mhalo~109-1012 M☉ Galaxy clusters: Mhalo~1014-1015 M☉

Clusters Galaxies

Two challenges: large cross section right velocity dependence

1 10 100 1000 104 0.001 0.010 0.100 1 10 dark matter relative velocity (km/s) σ/m (cm2/g)

Galaxy clusters σ/m<~0.1 cm2/g Galaxies σ/m~3 cm2/g

A Simple SIDM Model

• Self-scattering kinematics determines SIDM mass

Fix αX=1/137 Predict: mX~15 GeV, mɸ ~17 MeV

with Kaplinghat, Tulin (PRL 2015)

V (r) = αX r e−mφr

X X X X ɸ

Yukawa potential

σ ∼ 1/v4

σ ∼ const q ⌧ mφ q mφ

Other models: Chu, Garcia-Cely, Murayama (2018, 2019)

The nightmare scenario is not hopeless!

N-P vs. DM-DM Scatterings

Tulin & HBY (2017); data from Obloinsk+(2011)

σ ∼ 1/v4

σ ∼ const

q ⌧ mφ q mφ

SIDM Direct Detection

PandaX-II collaboration+HBY (PRL, 2018)

N X X N

ɸ WIMP: mɸ~1 TeV>>q SIDM: mɸ~10 MeV~q

Smoking-gun signature

SIDM at Colliders

• Striking collider signals

⟿

X X p

p

_

Visible

Invisible

pp→Monojet+Missing Energy

WIMP SIDM

With Tsai, Xu (JHEP , 2018)

Dark Matter “Colliders”

Dwarf galaxies MW-like galaxies Clusters

“B-factory” (v~30 km/s) “LEP” (v~200 km/s) “LHC” (v~1000 km/s)

Observations

• n all scales

Self-scattering kinematics Measure particle physics parameters σX, mX, mɸ

Summary

• The nature of dark matter is one of the deepest mysteries.
• We have made tremendous progress in the search for dark

matter (WIMPs and Axions), but no convincing signals.

• “Hope for the best, but prepare for the worst.”
• Astrophysical observations coupled with particle physics

modeling and computer simulations can provide extremely powerful insight into the nature of dark matter.

X X X X X SM SM X

Thank You!

Thank you!