Dan Hooper

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Hot on the Trail of Particle Dark Matter

• Dan Hooper
• Particle Astrophysics Center
• Fermi National Laboratory
• dhooper_at_fnal.gov

University of Kansas April 17, 2006
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What do we know about dark matter?
3
What do we know about dark matter?
Ask An Astrophysicist
? A Great Deal!
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The Existence of Dark Matter
Vera Rubin Fritz Zwicky

• Galaxy and cluster rotation curves have pointed
  to the presence of large quantities of
  non-luminous matter for many decades (conclusive
  evidence since the 1970s)

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The Existence of Dark Matter
Vera Rubin Fritz Zwicky

• Galaxy and cluster rotation curves have pointed
  to the presence of large quantities of
  non-luminous matter for many decades (conclusive
  evidence since the 1970s)

In the new age of precision cosmology, we now
know much more!
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The Density of our Universe
The anisotropies in the cosmic microwave
background (CMB) have been studied to reveal the
curvature and density of our Universe
?tot ? 1
(about 10-29
grams/cm3)
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The Composition of Our Universe

• In addition to matter, general relativity allows
  for a cosmological term, L?(vacuum energy/dark
  energy)
• Quantum field theory would suggest that WL?
  1060, 10120, or 0
• So, we had expected to measure WL? 0

8
The Composition of Our Universe

• In addition to matter, general relativity allows
  for a cosmological term, L?(vacuum energy/dark
  energy)
• Quantum field theory would suggest that WL?
  1060, 10120, or 0
• So, we had expected to measure WL? 0
• Our expectations turned out to be wrong!

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The Composition of Our
Universe

• Compare expansion history of our Universe to the
  CMB anisotropies and cluster masses

Best fit to data
Flat, all matter Universe
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The Composition of Our
Universe

• Compare expansion history of our Universe to the
  CMB anisotropies and cluster masses
• In addition to matter, our Universe contains a
  great deal of dark energy (WL? 0.72)

Best fit to data
Flat, all matter Universe
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Whats The Matter?

• So 30 of our Universes density is in the form
  of matter (mostly dark matter, as seen from
  galaxy rotation curves, clusters, etc.)
• So what kind of matter is it?
• First guess Baryons (white dwarfs, brown dwarfs,
  neutron stars, jupiter-like planets, black holes,
  etc.)

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Baryon Abundance

• Big Bang nucleosynthesis combined with cosmic
  microwave background determine WBh2 ? 0.024
• ???WB 0.05
• But, we also know WM 0.3, so most of the matter
  in the Universe is non-baryonic!

Fields and Sarkar, 2004
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Cold Dark Matter and Structure Formation

• Observations of the large scale structure of our
  Universe can be compared to computer simulations
• Simulation results depend primarily on whether
  the dark matter is hot (relativistic) or cold
  (non-relativistic) when structures were formed
• Most of the Universes matter must be Cold Dark
  Matter

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The world is full of obvious thing which nobody
by any chance ever observes. -Sherlock Holmes

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What do we know about dark matter?
Ask An Astrophysicist
? A Great Deal!
16
What do we know about dark matter?
Ask An Astrophysicist
? A Great Deal!
Ask A Particle Physicist
?Next to Nothing (but we have some good guesses)
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The Particle Nature of Dark Matter
Axions, Neutralinos, Gravitinos, Axinos,
Kaluza-Klein States, Heavy Fourth Generation
Neutrinos, Mirror Particles, Stable States in
Little Higgs Theories, WIMPzillas, Cryptons,
Sterile Neutrinos, Sneutrinos, Light Scalars,
Q-Balls, D-Matter, SuperWIMPS, Brane World Dark
Matter,

• A virtual zoo of dark matter candidates have been
  proposed over the years. 100s of viable
  candidates.
• Weakly Interacting Massive Particles (WIMPs) are
  a particularly attractive class of dark matter
  candidates.

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The Thermal Abundance of a WIMP

• Stable particle, X, in thermal equilibrium in
  early Universe (freely created and annihilated,
  roughly as plentiful as ordinary types of matter)
• As Universe cools, number density of X becomes
  Boltzman suppressed
• But expansion of the Universe makes finding Xs
  to annihilate with difficult, suppressing the
  annihilation rate

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The Thermal Abundance of a WIMP

• Expansion leads to a thermal freeze-out of X
  particles
• For a particle with weak scale interactions,
  freeze-out occurs at a temperature, TMX/20
• With weak scale interactions, freeze out leads to
  a density of X particles of ?1

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The Thermal Abundance of a WIMP

• Expansion leads to a thermal freeze-out of X
  particles
• For a particle with weak scale interactions,
  freeze-out occurs at a temperature, TMX/20
• With weak scale interactions, freeze out leads to
  a density of X particles of ?1

Automatically generates observed relic density!!!
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Supersymmetry

• Elegant extension of the Standard Model
• For each fermion in nature, a corresponding boson
  must also exist (and vice versa)
• New spectrum of superpartner particles yet to
  be discovered

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Why Supersymmetry?

• Not introduced for dark matter

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Why Supersymmetry?

• Not introduced for dark matter
• Higgs mass stability

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Supersymmetry and the Mass of the Higgs Boson

• Electroweak precision observables indicate the
  presence of a light Higgs boson (around 100 GeV)
• Large contributions to the Higgs mass come from
  particle loops

• Without SUSY, ? MGUT or MPlanck? ultra-heavy
  Higgs
• With TeV scale SUSY, boson and fermion loops
  nearly cancel
• ? light Higgs

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Why Supersymmetry?

• Not introduced for dark matter
• Higgs mass stability
• Grand Unification

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Supersymmetry and Grand Unification

• If there is a Grand Unified Theory (GUT) in
  nature, then we expect the SM forces to become of
  equal strength at some high energy scale
• In the Standard Model, couplings become
  similar, but not equal

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Supersymmetry and Grand Unification

• With Supersymmetry, the three forces can unify at
  a single scale

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Supersymmetry and Dark Matter

• For the proton to be sufficiently stable,
  R-parity must be conserved
• Evenness or oddness of superpartners is conserved
• Consequence the Lightest Supersymmetric Particle
  (LSP) is stable, and a potentially viable dark
  matter candidate
• The identity of the LSP depends on the mechanism
  of supersymmetry breaking

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The Lightest Supersymmetric Particle

• Dark matter candidates must be electrically
  neutral, not colored
• Possibilities
• photino
• Zino
• (neutral) higgsinos
• sneutrinos
• gravitino
• axino

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The Lightest Supersymmetric Particle

• Dark matter candidates must be electrically
  neutral, not colored
• Possibilities
• photino
• Zino
• (neutral) higgsinos
• sneutrinos
• gravitino
• axino

Do not naturally generate the observed dark
matter density
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The Lightest Supersymmetric Particle

• Dark matter candidates must be electrically
  neutral, not colored
• Possibilities
• photino
• Zino
• (neutral) higgsinos
• sneutrinos
• gravitino
• axino

Ruled out by direct detection
Do not naturally generate the observed dark
matter density
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The Lightest Supersymmetric Particle

• Dark matter candidates must be electrically
  neutral, not colored
• Possibilities
• photino
• Zino
• (neutral) higgsinos
• sneutrinos
• gravitino
• axino

Mix to form 4 neutralinos
Ruled out by direct detection
Do not naturally generate the observed dark
matter density
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How To Search For A WIMP

• Direct Detection
• Indirect Detection
• Colliders

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Direct Detection

• Underground experiments hope to detect recoils of
  dark matter particles elastically scattering off
  of their detectors
• Prospects depend on the WIMPs elastic scattering
  cross section with nuclei
• Leading experiments include CDMS (Minnesota),
  Edelweiss (France), and Zeplin (UK)

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Direct Detection

• Elastic scattering can occur through Higgs and
  squark exchange diagrams

?
?
?
?

q
h,H
q
q
q
q
SUSY Models

• Cross section depends on numerous SUSY
  parameters neutralino mass and composition,
  tan?, squark masses and mixings, Higgs masses and
  mixings

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Direct Detection

• Current Status

Zeplin, Edelweiss
DAMA
CDMS
Supersymmetric Models

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Direct Detection

• Near-Future Prospects

Zeplin, Edelweiss
DAMA
CDMS
Supersymmetric Models
CDMS, Edelweiss Projections

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Direct Detection

• Long-Term Prospects

Zeplin, Edelweiss
DAMA
CDMS
Supersymmetric Models
Super-CDMS, Zeplin-Max

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Indirect Detection

• Attempt to observe annihilation products of dark
  matter annihilating in halo, or elsewhere
• Prospects depend on both the characteristics of
  the dark matter particle and its distribution in
  the halo
• Gamma-rays, neutrinos, positrons, anti-protons
  and anti-deuterons each provide a potentially
  viable channel for the detection of dark matter

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Indirect Detection Anti-Matter

• Matter and anti-matter generated equally in dark
  matter annihilations (unlike other processes)
• Cosmic positron, anti-proton and anti-deuteron
  spectrum may contain signatures of particle dark
  matter
• Upcoming experiments (PAMELA, AMS-02) will
  measure the cosmic anti-matter spectrum with much
  greater precision, and at much higher energies

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Indirect Detection Positrons

• Positrons produced through a range of dark matter
  annihilation channels
• (decays of heavy quarks, heavy leptons, gauge
  bosons, etc.)
• Positrons move under influence of galactic
  magnetic fields
• Energy losses through inverse compton and
  synchotron scattering with starlight, CMB

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Indirect Detection Positrons

• Determine positron spectrum at Earth by solving
  diffusion equation

Energy Loss Rate
Diffusion Constant
Source Term

• Inputs
• Diffusion constant
• Energy loss rate
• Annihilation cross section/modes
• Halo profile (inhomogeneities?)
• Boundary conditions
• Dark matter mass

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Indirect Detection Positrons

• Reduce systematics by studying the positron
  fraction
• When plotted this way, HEAT experiment observes a
  significant excess

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Indirect Detection Positrons
Supersymmetric (neutralino) origin of positron
excess? -Spectrum generated by annihilating
neutralinos can fit the HEAT data

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Indirect Detection Positrons
Supersymmetric (neutralino) origin of positron
excess? -Spectrum generated by annihilating
neutralinos can fit the HEAT data -Normalization
is another issue

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Indirect Detection Positrons

• The Annihilation Rate (Normalization)
• -If a thermal relic is considered, a large degree
  of local
• inhomogeneity (boost factor) is
  required in dark matter halo
• -Might local clumps of dark matter accommodate
  this?
• Two mass scales
• -Sum of small mass (10-1 - 10-6 M?) clumps
• ? Small boost (2-10, whereas 50 or
  more is required)
• -A single large mass clump (104 - 108 M?)
• ? Unlikely at 10-4 level

Hooper, J. Taylor and J. Silk, PRD
(hep-ph/0312076) H. Zhao, J. Taylor, J. Silk and
Hooper (hep-ph/0508215)
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Indirect Detection Positrons
Where does this leave us?

• Future cosmic positron experiments hold great
  promise
• PAMELA satellite, planned to be launched in 2006
• AMS-02, planned for deployment
• onboard the ISS (???)

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Indirect Detection Positrons
With a HEAT sized signal

• Dramatic signal for either PAMELA or AMS-02
• Clear, easily identifiable signature of dark
  matter

Hooper and J. Silk, PRD (hep-ph/0409104)
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Indirect Detection Positrons
With a smaller signal

• More difficult for PAMELA or AMS-02
• Still one of the most promising dark matter
  search techniques

Hooper and J. Silk, PRD (hep-ph/0409104)
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Indirect Detection Positrons
Prospects for Neutralino Dark Matter

• AMS-02 can detect a thermal (s-wave) relic up
  to 200 GeV, for any boost factor, and all likely
  annihilation modes
• For modest boost factor of 5, AMS-02 can detect
  dark matter as heavy as 1 TeV
• PAMELA, with modest boost factors, can reach
  masses of 250 GeV
• Non-thermal scenarios (AMSB, etc), can be easily
  tested

Value for thermal abundance
Hooper and J. Silk, PRD (hep-ph/0409104)
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Indirect Detection Neutrinos

• WIMPs elastically scatter with massive bodies
  (Sun)
• Captured at a rate 1018 s-1 (??p/10-8 pb) (100
  GeV/m?)2
• Over billions of years, annihilation/capture
  rates equilibrate
• Annihilation products are absorbed, except for
  neutrinos

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Indirect Detection Neutrinos

• The IceCube Neutrino Telescope
• Full cubic kilometer instrumented volume
• Technology proven with predecessor, AMANDA
• First string of detectors deployed in 2004/2005,
• 8 more strings deployed in 2005/2006 (80 in
  total)
• Sensitive to muon neutrinos above 100 GeV
• Similar physics reach to KM3 in
• Mediterranean Sea

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Indirect Detection Neutrinos

• Neutrino flux depends on the capture rate, which
  is in turn tied to the elastic scattering cross
  section
• Direct detection limits impact rates anticipated
  in neutrino telescopes

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Indirect Detection Neutrinos

• WIMPs become captured in the Sun through
  spin-independent and spin-dependent scattering
• Direct detection constraints on spin-dependent
  scattering are still very weak

Spin-Dependent
Spin-Independent
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Indirect Detection Neutrinos
What Kind of Neutralino Has a Large
Spin-Dependent Coupling?
?
Z
q
q
q
q
q
q
Always Small
? fH12 - fH22
Substantial Higgsino Component Needed
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Indirect Detection Neutrinos
What Kind of Neutralino Has a Large
Spin-Dependent Couplings?
Large Rate At IceCube/KM3
Large Rate in IceCube/KM3


F. Halzen and Hooper (hep-ph/0510048)
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Indirect Detection Gamma-Rays

Advantages of Gamma-Rays

• Propagate undeflected (point sources possible)
• Propagate without energy loss (spectral
  information)
• Distinctive spectral features (lines), provide
  potential smoking gun
• Wide range of experimental technology (ACTs,
  satellite-based)

Disadvantages of Gamma-Rays

• Flux depends critically on poorly known inner
  halo profiles
• ? predictions dramatically vary from model
  to model
• Astrophysical backgrounds

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Indirect Detection Gamma-Rays
The Galactic Center Region

• Likely to be the brightest source of dark matter
  annihilation radiation
• Detected in TeV gamma-rays by three
• ACTs Cangaroo-II, Whipple and HESS
• Possible evidence for dark matter?

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Indirect Detection Gamma-Rays

The Cangaroo-II Observation

• Consistent with WIMP in 1-4 TeV mass range
• Roughly consistent with Whipple/Veritas

Hooper, Perez, Silk, Ferrer and Sarkar, JCAP,
astro-ph/0404205
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Indirect Detection Gamma-Rays

The Cangaroo-II Observation

• Consistent with WIMP in 1-4 TeV mass range
• Roughly consistent with Whipple/Veritas

The HESS Obsevation

• Superior telescope
• Inconsistent with Cangaroo-II
• Extends at least to 10 TeV
• WIMP of 10-40 TeV mass needed

D. Horns, PLB, astro-ph/0408192
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Indirect Detection Gamma-Rays

Can A Neutralino Be As Heavy As 10-40 TeV?

• Very heavy neutralinos tend to overclose the
  Universe
• Neutralinos heavier than a few TeV require fine
  tuning (through coannihilations) to evade too
  much relic density (S. Profumo, hep-ph/0508628)
• If superpartners are heavier than a few TeV, then
  the Higgs mass is no longer naturally light (one
  of the primary motivations for supersymmetry in
  the first place)

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Indirect Detection Gamma-Rays

Can A Neutralino Be As Heavy As 10-40 TeV?

• Very heavy neutralinos tend to overclose the
  Universe
• Neutralinos heavier than a few TeV require fine
  tuning (through coannihilations) to evade too
  much relic density (S. Profumo, hep-ph/0508628)
• If superpartners are heavier than a few TeV, then
  the Higgs mass is no longer naturally light (one
  of the primary motivations for supersymmetry in
  the first place)

?10-40 TeV Supersymmetry is extremely unattractive
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Indirect Detection Gamma-Rays
Messenger Sector Dark Matter

• In Gauge Mediated SUSY Breaking (GMSB) models,
  SUSY is broken in 100 TeV sector
• LSP is a light gravitino (1-10 eV), poor DM
  candidate
• Lightest messenger particle is naturally stable,
  multi-TeV scalar neutrino is a viable dark matter
  candidate

Dimopolous, Giudice and Pomarol, PLB
(hep-ph/9607225) Han and Hemfling, PLB
(hep-ph/9708264) Han, Marfatia, Zhang, PRD
(hep-ph/9906508) Hooper and J. March-Russell,
PLB (hep-ph/0412048)
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Indirect Detection Gamma-Rays
Messenger Sector Dark Matter

• Gamma-ray spectrum (marginally) consistent with
  HESS data
• Normalization requires highly cuspy,
• compressed, or spiked halo profile
• With further HESS observation of
• region, dark matter hypothesis should
• be conclusively tested
• Source appears increasingly likely to
• be of an astrophysical origin

Hooper and J. March-Russell, PLB (hep-ph/0412048)
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Astrophysical Origin of Galactic Center Source?

• A region rich in extreme astrophysical objects
• Particle acceleration associated with
  supermassive black hole?
• Aharonian and Neronov (astro-ph/0408303),
• Atoyan and Dermer (astro-ph/0410243)
• Nearby Supernova Remnant to close
• to rule out
• If this source is of an astrophysical
• nature, it would represent a extremely
• challenging background for future
• dark matter searches to overcome
• (GLAST, AMS, etc.)
• (Zaharijas and Hooper, astro-ph/0603540)

Hooper, Perez, Silk, Ferrer and Sarkar, JCAP,
astro-ph/0404205
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Indirect Detection Gamma-Rays
Dwarf Spheriodal Galaxies

• Several very high mass-to-light dwarf galaxies in
  Milky Way
• (Draco, Sagittarius, etc.)
• Little is known for certain about the halo
  profiles of such objects
• For example, draco mass estimates range from 107
  to 1010 solar masses
• ? broad range of predictions for
  annihilation rate/gamma-ray flux
• May provide several very bright sources of dark
  matter annihilation radiation or very, very
  little
• Detection of Draco by CACTUS experiment???
• (Bergstrom Hooper, hep-ph/0512317 Profumo
  Kamionkowski, astro-ph/0601249)

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How To Search For A WIMP Colliders

• If mDM mEW (along with associated particles),
• discovery likely at LHC
  and/or Tevatron
• Strong constraints from LEP data

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Supersymmetry At The Tevatron

• Most promising channel is through
  neutralino-chargino production
• For example,
• Tevatron searches for light squarks and gluinos
  are also interesting
• Tevatron SUSY searches only possible if
• superpartners are rather light

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Supersymmetry At The LHC

• Squarks and gluinos will be produced prolificly
  at the LHC (probably discovered within first
  month of running)
• Squarks/gluinos decay to leptonsjetsmissing
  energy (LSPs)
• Lightest neutralino mass to be measured to 10
  precision
• But is it dark matter?
• Calculated relic density should be
• compared to CDM density

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Putting It All Together

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Summary

• Very exciting prospects exist for direct,
  indirect and collider searches for dark matter
• Cosmic anti-matter searches will be sensitive to
  thermally produced (s-wave) WIMPs up to
  hundreds of GeV (PAMELA) or 1 TeV (AMS-02)
• Kilometer scale neutrino telescopes (IceCube,
  KM3) will be capable of detecting mixed
  gaugino-higgsino neutralinos
• Gamma-ray astronomy is improving rapidly, but it
  is difficult to predict the prospects for dark
  matter detection given the astrophysical
  uncertainties Dwarf spheriodals are among the
  most promising sources

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The Cork Is Still In the Champagne Bottle

• Furthermore
• Direct detection experiments (CDMS) have
• reached 10-7 pb level, with 1-2 orders of
• magnitude expected in near future (many
• of the most attractive SUSY models)
• Collider searches (LHC, Tevatron) are
• exceedingly likely to discover Supersymmetry
• or whatever other new physics is associated
• with the electroweak scale

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But Maybe Not For Long