The document discusses evidence for dark matter from astrophysical observations. It is established that dark matter is massive, cold, collisionless, and does not interact electromagnetically. However, its fundamental nature and interactions are unknown. The evidence includes missing mass observations from galaxy rotation curves, cluster dynamics, gravitational lensing as well as cosmological measurements of the cosmic microwave background and matter power spectrum. Future experiments aim to directly detect dark matter particle signatures through anomalies in cosmic ray spectra or indirect signals from early structure formation.

1. Insights into Dark Matter
Hints and Signals from Astrophysics
Katherine J. Mack
University of Melbourne
www.ph.unimelb.edu.au/~kmack
: @AstroKatie
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2. a slice of the universe pie
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3. what we know
Dark matter is:
Massive (gravitationally attractive & clustering)
Cold (slow-moving)
Collisionless (passes through itself and other matter)
Dark (does not emit or absorb light)
Non- (or weakly-) interacting (no detected non-
gravitational interactions with other particles)
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4. what we don’t know
Fundamental nature of dark matter
How dark matter formed in the universe
Whether dark matter has any non-gravitational
interaction with standard model particles
Whether dark matter has any non-gravitational
interaction with itself
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5. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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6. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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7. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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8. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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9. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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10. cosmological microlensing
ESO
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11. cosmological microlensing
1454 MEDIAVILLA ET AL. Vol. 706
α=0.01 α=0.05 α=0.1
Lensing of background
quasars by galaxies can
give insight into galaxy
mass distributions α=0.15 α=0.2 α=0.25
Constraints can be
placed on fraction of
mass in compact α=0.3 α=0.5 α=1
sources (stars)
Constraint: α < 10%
Figure 2. Example of magnification maps for the case κ = γ = 0.45. From top to bottom and from left to right, maps correspond to α = 0.01, 0.05, 0.10, 0.15, 0.20,
0.25, 0.30, 0.50, 1.00.
Mediavilla et al. 2009
2. OBSERVED MICROLENSING MAGNIFICATIONS AND For some of the image pairs (∼30% of the sample) there
MACRO-LENS MODELS are mid-IR flux ratios available. Except for one system, SDSS
J1004+4112 (where image C is probably affected by extinction,
We collected the data, ∆m (see Equation (4)), examining all ´
G´ mez-Alvarez et al. 2006), they are in very good agreement
o
the optical spectroscopy5 found in the literature (see Table 1). In with the emission-line flux ratios (see Table 2). The average
most cases, the microlensing magnification or the scaling of the difference between mid-IR and emission line flux ratios is only
Tuesday, 5 March 13 emission line ratio with respect to the continuum ratio are di- 11

12. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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13. WMAP 9
SPT
ACT
Hinshaw et al. 2013
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14. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo shapes /
substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon
ratio)
Cluster collisions (missing mass / collisionless matter)
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15. Tuesday, 5 March 13 15

16. the evidence amasses
Rotation curves & galactic dynamics (missing mass)
Cluster dynamics (missing mass)
Strong & weak gravitational lensing (missing mass / halo
shapes / substructure)
Gravitational microlensing (smooth distribution of mass)
CMB acoustic peaks (DM/baryon ratio)
Matter power spectrum & structure formation (DM/baryon ratio)
Cluster collisions (missing mass / collisionless matter)
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17. dark matter’s smoking gun:
the Bullet Cluster
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18. dark matter’s smoking gun:
the Bullet Cluster
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19. dark matter’s smoking gun:
the Bullet Cluster
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20. dark matter’s smoking gun:
the Bullet Cluster
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21. classes of dark matter
Annihilating DM (e.g., SUSY neutralino WIMP)
Decaying DM (e.g., axino)
Warm DM (WDM) (e.g., sterile neutrino)
Self-interacting DM (SIDM) (particle + dark sector force)
Axion DM (e.g., QCD axion / string axion)
MACHO DM (e.g., primordial black holes)
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22. small-scale power
Dark matter particle interactions alter structure on small
scales (smaller than galaxies, clusters)
Look at: Lyman-alpha forest, substructures, satellites...
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23. missing satellites problem
Milky Way seems to have
fewer satellite galaxies
than expected in CDM
simulations
Caveats:
MW may not be typical
Baryonic effects might
account for dearth (see
Madau et al. 2008 e.g. Brooks et al. 2013)
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24. Navarro, Frenk & White 1997
cusp/core problem r -1
r -3
Inner profiles of galaxies observed
to flatten out (to a constant-density
“core”)
Self-interacting & warm dark matter
models sometimes invoked
BUT could be solved with baryon
physics
Supernova feedback can expel
gas from galaxy non-
adiabatically
This can flatten the DM cusp
into a core
Pontzen & Governato 2012
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25. warm dark matter
WDM has a free-streaming scale
within which structures are smooth
“Erases” small-scale structure in
the matter power spectrum
Invoked for substructures,
satellites
Constrained by Lyman-alpha forest
measurements
BUT: core size - mass relation Bode, Ostriker & Turok
2001
doesn’t hold up
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26. self-interacting DM
Has been proposed to explain cores in
galaxies and low numbers of substructures
Yoshida et al. 2000
in dark matter halos
Effects:
fewer substructures
smoother structure
cored inner density profiles
Currently being tested with cluster collision
modelling
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27. cosmic ray excesses
Positron excess seen at PAMELA experiment, confirmed with Fermi
Hints of e+ + e- spectrum feature; no antiproton excess
3 TeV DM with high cross-section proposed as explanation
Cirelli 2012
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28. cosmic ray excesses
Positron excess seen at PAMELA experiment, confirmed with Fermi
Hints of e+ + e- spectrum feature; no antiproton excess
3 TeV DM with high cross-section proposed as explanation
3 TeV DM particle
annihilating into τ+τ− with
cross section 2 · 10−22 cm3/
sec
Cirelli 2012
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29. cosmic ray excesses
BUT it could be
pulsars
No directional
information
available
Pulsars are known
to produce
electron/positron
pairs Grasso et al. 2009
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30. 130 GeV line(s) in Galactic Center
Hints have been seen by the Fermi
satellite of emission around 130
GeV from the Galactic Center
Best fit actually two lines Su & Finkbeiner 2012
Line emission could be a “smoking
gun” of DM annihilation -- hard to
make with astrophysics
BUT signal significance currently
low & some observational
uncertainties remain
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31. future: signatures at early times
Dark matter annihilation or
decay can alter the M.E.DE.A. code
M.Valdés, CE, A.Ferrara, MNRAS, 2011
evolution of the
intergalactic medium
heating
Energy injection heats & injected particle
ionizes gas
Lyman photons ionization
Signals may be seen in Image from talk by Carmello Evoli
• MEDEA follows every particle from TeV down to eV energies in a continuous way.
redshifted 21cm line of • Previous works have considered electrons up to keV only
(e.g. J.M.Shull & M.E. van Steenberg, APJ, 1985; S.Furlanetto & S.J.Stoever,!MNRAS, 2010).
neutral hydrogen giovedì 26 aprile 12
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32. outlook
Future data (Fermi, AMS, PAMELA, etc) will help pin
down anomalies
Simulations and modelling needed to check on
possible inconsistencies / hints
More accurate modelling of DM+baryon physics (to
make DM identification possible) (→Alan Duffy)
Cosmological models that include dark matter
physics (to see effects at early times) (→me+group)
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33. dark matter annihilates
altered radiation field dark matter halos heat
at early times themselves
altered small-scale
power
altered Pop III /
change in IGM dark stars
evolution (heating/
ionization)
change in SMBH production
from direct collapse /
altered H2 abundance quasistars
DRAGONS
(Dark-ages Reionization And
Galaxy Formation Simulation)
21cm global 21cm power
signal spectrum
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34. up for discussion
What does the particle physics community want from
the astronomers?
What kind of signal would convince us we’ve seen dark
matter particle physics?
Should we still be considering dark matter alternatives /
modified gravity?
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