Diverse Galactic Rotation Curves & Self-Interacting Dark Matter

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1 Diverse Galactic Rotation Curves & Self-Interacting Dark Matter Hai-Bo Yu University of California, Riverside TeVPA, August 7, 2017 See Anna Kwa s talk Review for Physics Reports: Sean Tulin, HBY arxiv:

2 ΛCDM Cosmology Success on large scales: larger than ~ kpc Crisis on small scales: galactic scales, < kpc Core vs. Cusp Diversity Missing Satellites Too-Big-To-Fail

3 Core vs. Cusp Problem DM-dominated systems (dwarfs, LSBs) s r s /r 0 s r/r s (1 + r/r s ) 2 Navarro, Frenk, White (1996) universal density profile, NFW profile ρs and rs are strongly correlated Many dwarf galaxies prefer a shallow density core, instead of a steep cusp

4 The Diversity Problem All galaxies have the same Vmax! Colored bands: hydrodynamic simulations of ΛCDM Oman et al. (2015) See also Kuzio de Naray, Martinez, Bullock, Kaplinghat (2009)

5 A Big Challenge for ΛCDM Circular Velocity at 2 kpc (km/s) Mhalo~ M Maximal Circular Velocity (km/s) Oman et al. (2015) Vcirc(2kpc) has a factor of 3-4 scatter for fixed Vmax

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

7 Self-Interacting Dark Matter Self-interactions thermalize the inner halo NFW σ/m X =2 cm 2 /g MW-sized halo Isothermal distribution SIDM SIDM Heat DM NFW σ/m X ~ 1 cm 2 /g From Huo & Sameie (UCR SIDM code) ' n v =( /m X ) v H 0 Spergel, Steinhardt (2000) Tulin, HBY (2017) for a review Ideal gas: PV=nRT

8 Modelling SIDM Halos The model works well remarkably 10 8 Red: NFW; Blue: SIDM simulations; Black: Analytical Model σ/m X =2 cm 2 /g MW-sized halo DM velocity dispersion Simulations: 119 km/s Model: 122 km/s Density (M /kpc 3 ) e tot/ 2 0 tot = dm + b r1 also tested with MIT/UCI simulation results MIT: Vogelsberger et al. (2012) UCI: Rocha et al., Peter et al. (2012) isothermal distribution Ideal gas: PV=nRT Radius (kpc) s r/r s (1 + r/r s ) 2 with Kaplinghat, Tulin (PRL 2015) with Kamada, Kaplinghat, Pace (PRL 2016)

9 Addressing the Diversity Problem DM self-interactions thermalize the inner halo 200 Observations - NFW 80 V max =70 km/s 60 Vcirc (2 kpc) (km/s) Vcir (km/s) 40 2σ range of concentration CDM SIDM only V max (km/s) Radius (kpc) DM-dominated galaxies: Lower the central density and the circular velocity Isothermal distribution X e tot/ 2 0 e X / 2 0 with Kamada, Kaplinghat, Pace (PRL 2016)

10 High Luminous Galaxies DM self-interactions tie DM together with baryons Vcirc (2 kpc) (km/s) Observations - NFW Density (MSun/kpc 3 ) Increasing baryon concentration V max =120 km/s, M D =10 10 M CDM SIDM,R D =2 SIDM,R D =3 SIDM,R D =6 SIDM only V max (km/s) Radius (kpc) Thermalization leads to higher DM density due to the baryonic influence X e tot/ 2 0 e B/ 2 0 with Kamada, Kaplinghat, Pace (PRL 2016) with Kaplinghat, Keeley, Linden (PRL 2013) with Kaplinghat, Linden (PRL 2013)

11 Solving the Diversity Problem See Anna s talk: ~120 galaxies Scatter in the halo concentration Spread in the baryon distribution Self-interactions tie the DM and baryon distributions together with Kamada, Kaplinghat, Pace (PRL 2016) (30 galaxies, Vmax= km/s)

12 Simulations Controlled N-body simulations: with Creasey, Sameie, Sales, Vogelsberger, Zavala (MNRAS 2016)

13 Density Cores in Galaxy Clusters Core size: ~10 kpc DM density HM ü êkpc 3 L 10 9 Cluster A stellar velocity HkmêsL NFW SIDM self-interacting r 1 collisionless radius HkpcL radius HkpcL Newman et al. (2013) with Kaplinghat, Tulin (PRL 2015) Clusters: Mhalo~ M Galaxies: Mhalo~ M

14 SIDM from Dwarfs to Clusters Consider 5 THINGS dwarfs (red), 7 LSBs (blue), 6 galaxy clusters (green) 8 simulated halos with σ/m=1 cm 2 /g (gray) for calibration Galaxies: ~2-3 cm 2 /g Clusters: ~0.1 cm 2 /g Core size in clusters: ~10 kpc If it were ~1 cm 2 /g in clusters, the core size would be ~100 kpc The strongest limit! DM halos as particle colliders with Kaplinghat, Tulin (PRL 2015)

15 Measuring Dark Matter Mass Self-scattering kinematics determines SIDM mass X X ɸ X X V (r) = X r e m r 10 αx=1/137 mx: ~15 GeV, m ɸ : ~17 MeV with Kaplinghat, Tulin (PRL 2015) σ/m (cm 2 /g) dark matter relative velocity (km/s)

16 Particle Physics of SIDM e Familiar examples in the visible sector e N ɣ π N Ion ɣ Ion e e N N Ion Ion sêm Hcm 2 êgl V (r) = EM r npænp elastic scattering V (r) = 1 r e m r V (r) = EM r e m Dr Other examples: atomic DM, SU(N) composite DM Need two scales to generate the v-dependence v rel HkmêsL Tulin, HBY (2017) Data: Obloinsk et al. (2011)

17 SIDM at Colliders Striking collider signals p X X WIMP Invisible Visible p _ J pc =0 -+ SIDM J pc =0 -- pp Monojet+Missing Energy An, Echenard, Pospelov, Zhang (PRL 2015) Tsai, Wang, Zhao (PRD 2015) Shepherd, Tait, Zaharijas (PRD 2009)

18 SIDM Direct Detection X N X N d dq 2 = 4 em X 2 Z 2 (q 2 + m 2 ) 2 v 2 q 2 =2m N E R WIMPs: m w >>q SIDM: m ɸ ~q with Del Nobile, Kaplinghat (JCAP 2015) with Kaplinghat, Tulin (PRD 2013) Experiments with different targets Annual modulation

19 Particle Properties XSIDM Tulin, HBY (2017)

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