Dark Matter: Hints and Signals from Astrophysics

Dark Matter
Hints and Signals from Astrophysics

Source: http://home.cern/about/physics/dark-matter

What do we know?
 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)

What we don’t know?
 Fundamental nature of dark matter
 How was it formed in the universe
 Whether it has any non-gravitational interaction
with the standard model particles
 Whether dark matter has any non-gravitational
interaction with itself

The evidence amasses
 Rotation curves & galactic dynamics (missing
mass)
 Cluster dynamics (missing mass)
 CMB acoustic peaks (DM/baryon ratio)
 Cluster collisions (missing mass/collisionless
matter)

Van Albada et al.
If mass was localised,
F = GMm/R2 = mv2/R
This gives the velocity profile as,
v = [GM/R]1/2
For v≈r,
M α r

Łokas et al. "Dark matter distribution in the Coma cluster from galaxy kinematics: breaking the mass–anisotropy degeneracy." Monthly Notices
of the Royal Astronomical Society 343.2 (2003): 401-412.

Netterfield, C. B., et al. "A measurement by BOOMERANG of multiple peaks in the angular power spectrum of the cosmic microwave background." The Astrophysical Journal 571.2
(2002): 604.
For the row corresponding to the age of our universe, the total matter density is about 34%
and the baryonic matter density is about 5.1%. Therefore the dark matter density comes out to
be about 28.9% of the universe and about 85% of the total matter density.
Thus, Baryonic Matter : Dark Matter is about 1:6

The evidence amasses
 Rotation curves & galactic dynamics (mssing
mass)
 Cluster dynamics (missing mass)
 CMB acoustic peaks (DM/baryon ratio)
 Cluster collisions (missing mass/collisionless
matter)

Gravitational Lensing
The angular positions of the images
are given by:-

The Bullet Cluster
NASA/STScl; ESO WFI; Magellan/u.Arizona/D.Clowe et al.

NASA/STScl; ESO WFI; Magellan/u.Arizona/D.Clowe et al.

Possible Candidates
 Annihilating DM (e.g. SUSY neutralino WIMP)
 Decaying DM (e.g. axino)
 Self-interacting DM (SIDM) (particle + dark
sector force)

Possible Candidates
 Annihilating DM (e.g. SUSY neutralino WIMP)
 Decaying DM (e.g. axion)
 Self-interacting DM (SIDM) (particle + dark
sector force)

WIMPs
 Weakly Interacting Massive Particles
 Mass range: 1 GeV – 1TeV (cannot be
neutrinos)
 Non-baryonic
 Thermally created in the early universe

The Early Universe
 Very high temperature
 Thermal equilibrium between matter and radiation
 nWIMP = nPhoton
 Universe cools → no. densities decrease
 Temperature<Mass of WIMP → Annihilation dominates
 nWIMP drops exponentially as em/T
 Density to low to cause annihilation, nWIMP becomes
constant
 Relic density is inversely proportional to the interaction
strength

Supersymmetry
 Symmetry between Bosons and Fermions
 Fermionic superpartner of a Boson: prefix ‘s’
 Bosonic superpartner of a Fermion: suffix ‘ino’
 Some have same quantum number
 Most stable: Lightest Supersymmetric Particle
(LSP)
 Typical LSP: Neutralino

Search for WIMPs
 Accelerator Searches:-
 Pair production of WIMPs & Initial or Final State
Radiation of a gluon, photon or a weak gauge
boson
 Scenario so far:-
 Small portion of mass range is explored
 Substantial regions of parameter space are
eliminated
 Prediction for Higgs Boson mass of about
120GeV (supersymmetry) has been verified

Search for WIMPs
Direct detection:-
Detecting energy deposited on scattering from a
nucleus: 1 keV – 100 keV
 Crystal dislocations
 Lattice vibrations (phonons)
 Ionizations (scintillation light or recoil of the ion)

Search for WIMPs
 Predicted range of event rate: 10-5 – 10
events/kg/day
 Current detection threshold: 1 event/kg/day

Search for WIMPs
Indirect detection:-

Axion
Proposed to solve the strong-CP problem with the
electroweak interactions in the Standard Model
 Neutral
 Very light: .05 -1.5 meV
 Could transform into a photon in the presence
of electromagnetic fields
 Could be produced in huge numbers after the
Big Bang

The Strong-CP Problem
CP (charge-parity) symmetry:-
 Interchange each particle by its antiparticle
 Invert the spatial coordinates
 If the physical law is equally valid → CP
symmetry
 Problem: Observed for strong but not observed
for electroweak interactions!
 Solution: Peccei-Quinn mechanism → axion

Detection of axions
Using intense magnetic fields (ADMX):-
 Microwave cavity immersed in 8 tesla magnet
 Resonant frequency is tuned to axion mass→
Interaction between halo axions and B
increases
 A tiny amount of power is deposited into the
cavity (less than 10-24 W)

Detection of axions
Detecting axions produced in solar interior
(CAST,IAXO):-
 Axions are produced by scattering from electric
charges (Primakoff Effect)
 Converting them back to X-ray photons
Conversion efficiency α B2 (9T in CAST)

Small Scale Deviations


Flores, Primack et.al (1994)
Boylin-Kolchin, Bullock et.al (2011)

Self-interacting DM
 Can still be usual WIMP
 MeV scale mediator particle
 DM-DM scattering cross section ~ 1 cm2/g
(weak force ~ 10-36 cm2/g)
Effects:-
 In-falling DM is scattered before reaching the
GC
 Phase Space Entropy increase → Shallower
density profile

Rocha, Miguel, et al. "Cosmological simulations with self-interacting dark matter–I. Constant-density cores and substructure." Monthly Notices of
the Royal Astronomical Society 430.1 (2013): 81-104.

References
 http://home.web.cern.ch/about/physics/dark-matter
 Van Albada, T. S., et al. "Distribution of dark matter in the spiral galaxy NGC 3198." Dark Matter in the
Universe 4 (2004): 7.
 Łokas, Ewa L., and Gary A. Mamon. "Dark matter distribution in the Coma cluster from galaxy kinematics:
breaking the mass–anisotropy degeneracy." Monthly Notices of the Royal Astronomical Society 343.2
(2003): 401-412.
 Netterfield, C. B., et al. "A measurement by BOOMERANG of multiple peaks in the angular power spectrum
of the cosmic microwave background." The Astrophysical Journal 571.2 (2002): 604.
 http://www.damtp.cam.ac.uk/user/db275/Cosmology
 http://www.astro.caltech.edu
 Mitsou, Vasiliki A. "Overview of searches for dark matter at the LHC." Journal of Physics: Conference Series.
Vol. 651. No. 1. IOP Publishing, 2015.
 Duffy, Leanne D., and Karl Van Bibber. "Axions as dark matter particles." New Journal of Physics 11.10
(2009): 105008.
 Haiman, Zoltan, Rennan Barkana, and Jeremiah P. Ostriker. "Warm dark matter, small scale crisis, and the
high redshift universe." AIP Conference Proceedings. Eds. J. Craig Wheeler, and Hugo Martel. Vol. 586. No.
1. AIP, 2001.
 Weinberg, David H., et al. "Cold dark matter: controversies on small scales." Proceedings of the National
Academy of Sciences 112.40 (2015): 12249-12255.
 https://digital.lib.washington.edu/researchworks/handle/1773/33559
 Rocha, Miguel, et al. "Cosmological simulations with self-interacting dark matter–I. Constant-density cores
and substructure." Monthly Notices of the Royal Astronomical Society 430.1 (2013): 81-104.
 Bertone, Gianfranco, Dan Hooper, and Joseph Silk. "Particle dark matter: Evidence, candidates and
constraints." Physics Reports 405.5 (2005): 279-390.
 http://cast.web.cern.ch/CAST/CAST.php
 http://iaxo.web.cern.ch/content/physics

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