the dark matter problem astrophysical probe of particle nature of dm 毕效军...
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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
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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 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
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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.
r
rGMvcirc
)(
The most direct evidence of the existence of dark matter.
Corbelli & Salucci (2000); Bergstrom (2000)
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dynamics of galaxy cluster
Virial theorem
U=2K K = mi vi
2
U ~ GM2/R
mass to light ratio (B) typical cluster: 100/h-300/h Sun
stellar pop: 1-10 Sun
critical: 1390 h +- 35%
Coma cluster
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X-ray cluster
hydrostatic equilibrium
beta model:
However, X-ray emission measures the temperature and M/Mvisible=20
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Strong Gravitational Lensing
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Weak Lensing mass reconstruction
RXJ1347.5-1145 (Bradac et al 2005)
Image ellipticity -> shear->
invert the equation
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Cosmological scalethe WMAP result
Spergel et al 2003
mh2=0.135+-0.009
m=0.27+-0.04
WMAP Combined fit:
Results depend on Supernovae and Hubble constant data.
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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
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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
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What we learned
In the universe there exists non-baryonic, non-hot, dark matter
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Problems at small scale of CDM
Galactic satellite problem and cusp at GC
Nature of dark matter or astrophysics process?
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Predicted number
Observed number of luminous satellite galaxies
• The predicted number of substructures exceeds the luminous satellite galaxies: dark substructures?
• Satellite galaxies are seen in Milky Way, e.g. Saggittarius, MCs
20km/s 100km/s10km/s
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The first dark halos
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.
Diemand, Moore, Stadel 2005
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Universal Density ProfileNFW profile
Navarro, Frenk, White 1997
CuspDark matter distribution—Density profile
Observation of rotation curve favors cored profile strongly
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Dark matter halo profile
simulation (Navarro, Frenk, white 1996): cusp
observation: core
NFW96, rotation curve
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Nature of dark matter or astrophysics process?
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missing satellites: CDM solution
• 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
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Alternatives to CDM
WDM: reduce the small scale powerSelf-Interacting Dark Matter (Spergel & Steinhardt 2000) Strongly Interacting Massive Particle Annihilating DMDecaying DMFuzzy DM
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WDM
From Jing 2000
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SIDM
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
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SIMP
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
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From particle physics
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Thermal history of the WIMP (thermal production)
ff
ff
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
fTv
scmh
13272 103
1326103~ scmv210~ GeVM 100weak~ 22/22 cv
WIMP is a natural dark matter candidate giving correct relic density (proposed trying to solve hierarchy problem).
Thermal equilibrium abundance
Hvn ~
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Collisional Damping and Free Streaming
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.
Kinetic decoupling at T ~ 1 MeV (Chen, Kamionkowski, Zhang 2001)
This is why we introduce hot, warm, and cold dark matter.
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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.
Direct detection
p
e+
_
indirect detection
llll
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Summary of the present limits
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PAMELA results of antiparticles in cosmic rays
Nature 458, 607 (2009)
Positron fraction Antiproton fraction
Phys.Rev.Lett.102:051101,2009
400+ citations after submitted on 28th Oct. 2008, 1paper per day
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The total electron+positron spectrum
Chang et al. Nature456, 362 2008
ATIC bump Fermi excess
Phys.Rev.Lett.102:181101,2009
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Primary positron/electrons from dark matter – 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.
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J. Zavala, M. Vogelsberger, and S. White, Astro-ph/0910.5221
Astro-ph/0911.0422
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Emission from the GC
Constraint on the central density of DM
TensionExist for the annihilating DM scenario,but consistent with decay scenario
Bi et al., 0905.1253
Liu, Yuan, Bi, Li, Zhang, 0906.3858
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Constraints on the minimal subhalos by observations of clusters
Standard CDM predicts the minimal subhalos
Observation constrains
Fermi limit to
DM is warm
A. Pinzke et al., 0905.1948
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Nonthermal production of dark matter 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
fTv
scmh
13272 103
Lin, Huang, Zhang, Brandenberger, PRL86,954 (2001)
Bi, Brandenberger, Gondolo, Li, Yuan, Zhang, 0905.1253
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