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 TAUP , 2019 TOYAMA, JAPAN September 10, 2019

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 Cold X Dark Stable None of the standard model particles can be a dark matter candidate DM candidates: WIMPs, Axions… See Hitoshi Murayama’s talk

WIMP/DM Search Status “ 上穷碧落下⻩黅泉，两处茫茫皆不⻅观。 ” ⽩百居易《⻓門恨歌》 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 ∼ 1 r ∼ 1 r 2 ∼ 1 r 3 ρ s Aquarius Project, Springel+ (2008) r/r s (1 + r/r s ) 2 CDM-only cosmological simulations Navarro-Frenk-White (NFW) profile (1996)

Core vs Cusp Problem • DM-dominated systems (dwarfs, LSBs) ∼ ρ s r s /r ∼ ρ 0 Tulin & HBY (2017) ρ s mass-to-light ratio r/r s (1 + r/r s ) 2 NFW (1996) Flores & Primack (1994); Moore (1994); de Blok & McGaugh (1997)…

Diversity Problem All galaxies have the same observed Vmax! Oman+(2015) Colored bands: hydrodynamical simulations of CDM (weak feedback)

A Big Challenge to CDM M halo ~10 9 -10 12 M ☉ cusp V circ (2kpc) has a core factor of ~4 scatter for fixed V max Reproduced from the data compiled in Oman+(2015)

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

Self-Interacting Dark Matter • Self-interactions thermalize the inner halo Isothermal distribution σ /m X =2 cm 2 /g MW-like halo CDM SIDM SIDM Heat DM CDM σ /m X ~1 cm 2 /g (nuclear scale) From Ran Huo Γ ' n σ v = ( ρ /m X ) σ v ⇠ H 0 Review: Tulin & HBY (Physics Reports 2017)

Addressing the Diversity Problem • DM self-interactions thermalize the inner halo 80 V max = 70 km / s 60 V cir ( km / s ) 2 σ range of concentration 40 20 CDM SIDM only σ /m=3 cm 2 /g 0 0 2 4 6 8 10 Radius ( kpc ) with Kamada, Kaplinghat, Pace (PRL 2017) DM-dominated galaxies: Lower the central density and the circular velocity Isothermal ρ X ∼ e − Φ tot / σ 2 0 ∼ e − Φ X / σ 2 0 distribution

High Surface Brightness Galaxies • DM self-interactions tie DM together with baryons Increasing baryon concentration 10 9 CDM SIDM,R D = 2 10 8 Density ( M Sun / kpc 3 ) SIDM,R D = 3 SIDM,R D = 6 10 7 SIDM only 10 6 V max = 120 km / s, M D = 10 10 M ⊙ 10 5 0.1 0.5 1 5 10 50 100 Radius ( kpc ) Thermalization leads to higher DM density due to the baryonic influence ρ X ∼ e − Φ tot / σ 2 0 ∼ e − Φ B / σ 2 0 with Kaplinghat, Keeley, Linden (PRL 2014) with Kaplinghat, Linden (PRL 2015) with Kamada, Kaplinghat, Pace (PRL 2017)

high concentration 100 high surface brightness 80 � ���� [ �� / � ] 60 low concentration low surface brightness 40 20 UGC05764 UGC07151 σ /m=3 cm 2 /g UGC07603 UGC08490 IC2574 UGC05750 NGC1705 UGC05721 0 0 2 4 6 8 10 12 14 ������ [ ��� ] • Intrinsic scatter in halo concentration • Diverse baryon distributions • SIDM thermalization ties DM and baryon distributions in the RIGHT way with Kamada, Kaplinghat, Pace (PRL 2017) σ /m=3 cm 2 /g 30 galaxies with Creasey, Sameie, Sales+ (MNRAS 2017)

A Much Larger Sample We fitted 147 galaxies (3.6 μ m band)! With Ren, Kwa, Kaplinghat (PRX, 2018) the SPARC sample, Lelli, McGaugh, Schombert (2016)

CDM w/Strong Feedback vs SIDM 100 80 � ���� [ �� / � ] 60 40 20 UGC05764 UGC07151 UGC07603 UGC08490 IC2574 UGC05750 NGC1705 UGC05721 0 0 2 4 6 8 10 12 14 ������ [ ��� ] Santos-Santos+(2017) Solid lines: SIDM fits Gray lines: NIHAO simulations of CDM (3 σ band) (~2 σ in the c 200 -M 200 relation) “strong/violent” feedback With Ren, Kaplinghat (to appear)

Model Comparison SIDM does better than any other model in the literature Red: CDM with strong feedback With Ren, Kaplinghat (to appear)

Beyond Field Galaxies σ /m=3 cm 2 /g Milky Way Satellite Galaxies with Sameie, Sales+ (2019) Valli & HBY (Nature Astronomy 2018) See also: Kahlhoefer+ (2019), Nishikawa+ (2019) Kaplinghat, Valli, HBY (2019) Dark matter self-interactions+Tidal interactions

SIDM from Dwarfs to Clusters Galaxies: M halo ~10 9 -10 12 M ☉ Galaxy clusters: M halo ~10 14 -10 15 M ☉ 10 Galaxies σ /m~3 cm 2 /g 1 Galaxies σ / m ( cm 2 / g ) Galaxy clusters 0.100 σ /m<~0.1 cm 2 /g Clusters 0.010 Two challenges: 0.001 10 4 1 10 100 1000 large cross section dark matter relative velocity ( km / s ) right velocity dependence With Kaplinghat, Tulin (PRL, 2015)

A Simple SIDM Model • Self-scattering kinematics determines SIDM mass X X ɸ X X V ( r ) = α X r e − m φ r Yukawa potential 10 with Kaplinghat, Tulin (PRL 2015) Fix α X =1/137 1 q ⌧ m φ σ / m ( cm 2 / g ) σ ∼ const Predict: m X ~15 GeV, m ɸ ~17 MeV 0.100 q � m φ 0.010 The nightmare scenario is not hopeless! σ ∼ 1 /v 4 0.001 1 10 100 1000 10 4 Other models: Chu, Garcia-Cely, Murayama (2018, 2019) dark matter relative velocity ( km / s )

N-P vs. DM-DM Scatterings 10 1 q ⌧ m φ σ / m ( cm 2 / g ) σ ∼ const 0.100 0.010 q � m φ σ ∼ 1 /v 4 0.001 1 10 100 1000 10 4 dark matter relative velocity ( km / s ) Tulin & HBY (2017); data from Obloinsk+(2011)

SIDM Direct Detection N X Smoking-gun signature ɸ WIMP: m ɸ ~1 TeV>>q SIDM: m ɸ ~10 MeV~q N X PandaX-II collaboration+HBY (PRL, 2018)

SIDM at Colliders • Striking collider signals SIDM WIMP ⟿ Visible _ p p X Invisible X pp → Monojet+Missing Energy 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) Self-scattering kinematics Measure particle Observations physics parameters on all scales σ X , m X , m ɸ

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 SM X X X SM X X

Thank You! Thank you!