dan hooper particle astrophysics center fermi national laboratory [email protected]
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Hot on the Trail of Particle Dark Matter. Dan Hooper Particle Astrophysics Center Fermi National Laboratory [email protected]. University of Kansas April 17, 2006. What do we know about dark matter?. What do we know about dark matter?. Ask An Astrophysicist:. A Great Deal!. - PowerPoint PPT PresentationTRANSCRIPT
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Dan HooperDan HooperParticle Astrophysics CenterParticle Astrophysics CenterFermi National LaboratoryFermi National Laboratory
[email protected]@fnal.gov
University of Kansas April 17, 2006
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What do we know about dark matter?
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What do we know about dark matter?
Ask An Astrophysicist:
A Great Deal!
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The Existence of Dark Matter
•Galaxy and cluster rotation curves have pointed to the presence of large quantities of non-luminous matter for many decades (conclusive evidence since the 1970’s)
Vera Rubin
Fritz Zwicky
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The Existence of Dark Matter
•Galaxy and cluster rotation curves have pointed to the presence of large quantities of non-luminous matter for many decades (conclusive evidence since the 1970’s)
Vera Rubin
Fritz Zwicky
In the new age of precision cosmology, In the new age of precision cosmology, we now know much more! 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, (vacuum energy/dark energy)
•Quantum field theory would suggest that ~ 1060, 10120, or 0
•So, we had expected to measure = 0
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The Composition of Our Universe
•In addition to matter, general relativity allows for a cosmological term, (vacuum energy/dark energy)
•Quantum field theory would suggest that ~ 1060, 10120, or 0
•So, we had expected to measure = 0
•Our expectations turned out to be wrong!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
Flat, all matter Universe
Best fit to data
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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 (~ 0.72)
Flat, all matter Universe
Best fit to data
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What’s The Matter?
•So ~30% of our Universe’s 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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•Big Bang nucleosynthesis combined with cosmic microwave background determine Bh2 0.024
B ~ 0.05
•But, we also know M ~ 0.3, so most of the matter in the Universe is non-baryonic!
Fields and Sarkar, 2004
Baryon Abundance
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•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 Universe’s matter must be Cold Dark Matter
Cold Dark Matter and Structure Formation
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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!
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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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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. 100’s of viable candidates.
•Weakly Interacting Massive Particles (WIMPs) are a particularly attractive class of dark matter candidates.
The Particle Nature of Dark Matter
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•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 X’s to annihilate with difficult, suppressing the annihilation rate
The Thermal Abundance of a WIMP
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•Expansion leads to a thermal freeze-out of X particles
•For a particle with weak scale interactions, freeze-out occurs at a temperature, T~MX/20
•With weak scale interactions, freeze out leads to a density of X particles of ~1
The Thermal Abundance of a WIMP
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•Expansion leads to a thermal freeze-out of X particles
•For a particle with weak scale interactions, freeze-out occurs at a temperature, T~MX/20
•With weak scale interactions, freeze out leads to a density of X particles of ~1
The Thermal Abundance of a WIMP
Automatically generates observed relic density!!!Automatically generates observed relic density!!!
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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
Supersymmetry
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Not introduced for dark matter
Why Supersymmetry?
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Not introduced for dark matter Higgs mass stability
Why Supersymmetry?
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•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
Supersymmetry and the Mass of the Higgs Boson
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Not introduced for dark matter Higgs mass stability Grand Unification
Why Supersymmetry?
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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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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
Supersymmetry and Dark Matter
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• Dark matter candidates must be electrically neutral, not colored
• Possibilities: photino Zino (neutral) higgsinos sneutrinos gravitino axino
The Lightest Supersymmetric Particle
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• Dark matter candidates must be electrically neutral, not colored
• Possibilities: photino Zino (neutral) higgsinos sneutrinos gravitino axino
The Lightest Supersymmetric Particle
Do not naturally generate the observed dark matter density
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• Dark matter candidates must be electrically neutral, not colored
• Possibilities: photino Zino (neutral) higgsinos sneutrinos gravitino axino
The Lightest Supersymmetric Particle
Do not naturally generate the observed dark matter density
Ruled out by direct detection
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• Dark matter candidates must be electrically neutral, not colored
• Possibilities: photino Zino (neutral) higgsinos sneutrinos gravitino axino
The Lightest Supersymmetric Particle
Do not naturally generate the observed dark matter density
Ruled out by direct detection
Mix to form 4 neutralinos
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•Direct Detection
•Indirect Detection
•Colliders
How To Search For A WIMP
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•Underground experiments hope to detect recoils of dark matter particles elastically scattering off of their detectors
•Prospects depend on the WIMP’s elastic scattering cross section with nuclei
•Leading experiments include CDMS (Minnesota), Edelweiss (France), and Zeplin (UK)
Direct Detection
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•Elastic scattering can occur through Higgs and squark exchange diagrams:
Direct Detection
q q
h,H
q q
q~
•Cross section depends on numerous SUSY parameters: neutralino mass and composition, tan, squark masses and mixings, Higgs masses and mixings
SUSY Models
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Direct Detection
•Current Status
CDMS
Zeplin, EdelweissDAMA
Supersymmetric
Models
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Direct Detection
•Near-Future Prospects
CDMS
Zeplin, EdelweissDAMA
Supersymmetric
Models CDMS, Edelweiss Projections
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Direct Detection
•Long-Term Prospects
CDMS
Zeplin, EdelweissDAMA
Supersymmetric
Models
Super-CDMS, Zeplin-Max
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•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
Indirect Detection
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•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
Indirect Detection: Anti-Matter
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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:
Diffusion Constant Energy Loss Rate Source TermInputs: •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
Hooper and J. Silk, PRD (hep-ph/0409104)
Value for thermal abundance
•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
Prospects for Neutralino Dark Matter:
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•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
Indirect Detection: Neutrinos
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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
Indirect Detection: Neutrinos
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•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
Indirect Detection: Neutrinos
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•WIMPs become captured in the Sun through spin-independent and spin-dependent scattering
•Direct detection constraints on spin-dependent scattering are still very weak
Indirect Detection: Neutrinos
Spin-Independent Spin-Dependent
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What Kind of Neutralino Has a Large Spin-Dependent Coupling?
Indirect Detection: Neutrinos
q q
Always Small |fH1|2 - |fH2|2
Substantial Higgsino Component Needed
Z
q q
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What Kind of Neutralino Has a Large Spin-Dependent Couplings?
Indirect Detection: Neutrinos
Large Rate At IceCube/KM3
F. Halzen and Hooper (hep-ph/0510048)
Large Rate in IceCube/KM3
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Advantages of Gamma-Rays
Indirect Detection: 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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The Galactic Center Region
Indirect Detection: Gamma-Rays
•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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The Cangaroo-II Observation
Indirect Detection: Gamma-Rays
•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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The Cangaroo-II Observation
Indirect Detection: Gamma-Rays
•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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Can A Neutralino Be As Heavy As 10-40 TeV?
Indirect Detection: Gamma-Rays
•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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Can A Neutralino Be As Heavy As 10-40 TeV?
Indirect Detection: Gamma-Rays
•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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Messenger Sector Dark Matter
Indirect Detection: Gamma-Rays
•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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Messenger Sector Dark Matter
Indirect Detection: Gamma-Rays
Hooper and J. March-Russell, PLB (hep-ph/0412048)
•Gamma-ray spectrum (marginally) consistent with HESS data
•Normalization requires highly cuspy, compressed, or spiked halo profile
•With further HESS observation ofregion, dark matter hypothesis shouldbe conclusively tested
•Source appears increasingly likely to be of an astrophysical origin
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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 astrophysicalnature, it would represent a extremelychallenging 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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Dwarf Spheriodal Galaxies
Indirect Detection: Gamma-Rays
•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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•If mDM~ mEW (along with associated particles), discovery likely at LHC and/or Tevatron
•Strong constraints from LEP data
How To Search For A WIMP: Colliders
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•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
Supersymmetry At The Tevatron
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•Squarks and gluinos will be produced prolificly at the LHC (probably discovered within first month of running)
•Squarks/gluinos decay to leptons+jets+missing 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
Supersymmetry At The LHC
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Putting It All Together
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•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
Summary
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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