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The Dark Matter Problem astrophysical probe of particle nature of DM. 毕效军 中国科学院高能物理所 2009/12/16. Outline. What we have learned from astrophysics evidence of DM and its abundance DM is not baryonic DM is not hot . “ problems ” of LCDM model

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The dark matter problem astrophysical probe of particle nature of dm

The Dark Matter Problem astrophysical probe of particle nature of DM





What we have learned from astrophysics

evidence of DM and its abundance

DM is not baryonic

DM is not hot

“problems” of LCDM model

cuspy halos and missing satellites

alternative models of DM

astrophysical answers

What we learned from particle physics

WIMP: the classic CDM

direct detection

indirect detection: excesses of electrons and positrons

non-standard CDM

Evidences galaxy scale
Evidences — galaxy scale

  • From the Kepler’s law, for r much larger than the luminous terms, you should have v∝r-1/2 However, it is flat or rises slightly.

  • The most direct evidence of the existence of dark matter.

Corbelli & Salucci (2000); Bergstrom (2000)

Dynamics of galaxy cluster
dynamics of galaxy cluster

Virial theorem

U=2K K =  mi vi2

U ~ GM2/R

Coma cluster

mass to light ratio (B)

typical cluster: 100/h-300/h Sun

stellar pop: 1-10 Sun

critical: 1390 h +- 35%

X ray cluster
X-ray cluster

hydrostatic equilibrium

beta model:

However, X-ray emission measures the temperature and M/Mvisible=20

Weak lensing mass reconstruction
Weak Lensing mass reconstruction

Image ellipticity -> shear->

invert the equation

RXJ1347.5-1145 (Bradac et al 2005)

Cosmological scale the wmap result
Cosmological scalethe WMAP result

Spergel et al 2003

WMAP Combined fit:



Results depend on Supernovae and Hubble constant data.

Non baryonic

From BBN and CMB, it has Bh2=0.02+-0.002. Therefore, most dark matter should be non-baryonic. DMh2=0.113+-0.009

Nature of the dark matter hot or cold
Nature of the dark matter—Hot or cold

  • Hot dark matter is relativistic at the collapse epoch and free-streaming out the galaxy-sized over density. Larger structure forms early and fragments to smaller ones.

  • Cold DM is non-relativistic

    at de-coupling, forms

    structure in a hierarchical,

    bottom-up scenario.

  • HDM is tightly bound from

    observation and LSS forma-

    tion theory

What we learned
What we learned

In the universe there exists non-baryonic, non-hot, dark matter

Problems at small scale of cdm
Problems at small scale of CDM

  • Galactic satellite problem and cusp at GC

  • Nature of dark matter or astrophysics process?

Predicted number

Observed number of luminous satellite galaxies




  • The predicted number of substructures exceeds the luminous satellite galaxies: dark substructures?

The first dark halos
The first dark halos MCs

Diemand, Moore, Stadel 2005

Due to collisional damping and free-streaming, the smallest halo (no sub-structure) is 10-6 solar mass (earth mass) for neutralino. Detection of such halo may probe the nature of DM.

Dark matter distribution—Density profile MCs


Observation of rotation curve favors cored profile strongly

Universal Density Profile

NFW profile

Navarro, Frenk, White 1997

Dark matter halo profile
Dark matter halo profile MCs

simulation (Navarro, Frenk, white 1996): cusp

observation: core

NFW96, rotation curve

Missing satellites cdm solution
missing satellites: CDM solution MCs

  • satellites do exist, but star formation suppressed (after reionization?)

  • satellites orbit do not bring them to close interaction with disk, so they will not heat up the disk.

  • Local Group dwarf velocity dispersion underestimated

  • halo substructure may be probed by lensing (still controversial)

  • galaxy may not follow dwarf

Alternatives to cdm
Alternatives to CDM MCs

WDM: reduce the small scale power

Self-Interacting Dark Matter (Spergel & Steinhardt 2000)

Strongly Interacting Massive Particle

Annihilating DM

Decaying DM

Fuzzy DM


From Jing 2000


DM strongly interact with itself, but no EM

interaction can create an core in hierachical scenario (eventually core collapse -> isothermal profile)

Interaction strength: comparable to neutron-neutron

Difficulty: make spherical clusters: against lensing


  • Motivation:

  • SIDM may have QCD interaction but not EM

  • Not detectable in WIMP search, blocked.

CMB & LSS constraint:

Before decoupling, photons and baryons are tightly coupled, interaction with baryon will cause additional damping of perturbation

Thermal history of the wimp thermal production
Thermal history of the WIMP (thermal production) MCs

Thermal equilibrium abundance

At T >> m,

At T < m,

At T ~ m/22, ,decoupled, relic density is inversely proportional to the interaction strength

For the weak scale interaction and mass scale (non-relativistic dark matter particles) , if and

WIMP is a natural dark matter candidate giving correct relic density (proposed trying to solve hierarchy problem).

Collisional damping and free streaming
Collisional Damping and Free Streaming MCs

Kinetic decoupling at T ~ 1 MeV (Chen, Kamionkowski, Zhang 2001)

Initial density perturbation is damped by the free streaming of the particles before radiation-matter equality

perturbations on scales smaller than rFS is smoothed out.

This is why we introduce hot, warm, and cold dark matter.

Detection of wimp

c MCs









Detection of WIMP

  • Indirect detection DM increases in Galaxies, annihilation restarts(∝ρ2); ID looks for the annihilation products of WIMPs, such as the neutrinos, gamma rays, positrons at the ground/space-based experiments

  • Direct detection of WIMP at terrestrial detectors via scattering of WIMP of the detector material.

indirect detection

Direct detection

Pamela results of antiparticles in cosmic rays
PAMELA results of antiparticles in cosmic rays MCs

Positron fraction

Antiproton fraction

Nature 458, 607 (2009)


400+ citations after submitted on 28th Oct. 2008, 1paper per day

The total electron positron spectrum
The total electron+positron spectrum MCs

ATIC bump

Fermi excess

Chang et al. Nature456, 362 2008


Primary positron electrons from dark matter implication from new data
Primary positron/electrons from dark matter MCs– implication from new data

  • DM annihilation/decay produce leptons mainly in order not to produce too much antiprotons.

  • Very hard electron spectrum -> dark matter annihilates/decay into leptons.

  • Very large annihilation cross section, much larger (~1000) than the requirement by relic density.

    • 1) nonthermal production,

    • 2) Sommerfeld enhancement

    • 3) Breit-Wigner enhancement

    • 4) dark matter decay.

J. Zavala, M. Vogelsberger, and S. White, Astro-ph/0910.5221


Emission from the gc
Emission from the GC Astro-ph/0910.5221

Bi et al., 0905.1253

  • Constraint on the central density of DM

  • Tension

    Exist for the


    DM scenario,

    but consistent

    with decay scenario

Liu, Yuan, Bi, Li, Zhang, 0906.3858

Constraints on the minimal subhalos by observations of clusters
Constraints on the minimal subhalos by observations of clusters

A. Pinzke et al., 0905.1948

  • Standard CDM predicts the minimal subhalos

  • Observation constrains

  • Fermi limit to

  • DM is warm

Nonthermal production of dark matter
Nonthermal production of dark matter clusters

  • 暗物质可以通过早期宇宙产物的衰变产生,这样的暗物质可以有很大的湮灭截面,同时产生的速度大,压低小尺度的结构。这样银心的伽马射线没有超出,因此受到的限制会减弱。

  • 银心的伽马射线、河外星系团、河外弥散伽马的限制可以满足

Lin, Huang, Zhang, Brandenberger, PRL86,954 (2001)

Bi, Brandenberger, Gondolo, Li, Yuan, Zhang, 0905.1253