Transcript Document 7454683
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!
The Existence of Dark Matter
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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
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)
In the new age of precision cosmology, we now know much more!
Vera Rubin Fritz Zwicky
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/cm 3 )
The Composition of Our Universe
•
In addition to matter, general relativity allows for a cosmological term,
L
(vacuum energy/dark energy)
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Quantum field theory would suggest that
L
~ 10 60 , 10 120 , or 0
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So, we had expected to measure
L
= 0
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
L
~ 10 60 , 10 120 , or 0
•
So, we had expected to measure
L
= 0
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Our expectations turned out to be wrong!
The Composition of Our Universe
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Compare expansion history of our Universe to the CMB anisotropies and cluster masses Best fit to data Flat, all matter Universe
The Composition of Our Universe
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Compare expansion history of our Universe to the CMB anisotropies and cluster masses
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In addition to matter, our Universe contains a great deal of dark energy (
L
~ 0.72) Best fit to data Flat, all matter Universe
What’s The Matter?
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So ~30% of our Universe’s density is in the form of matter (mostly dark matter, as seen from galaxy rotation curves, clusters, etc.)
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So what kind of matter is it?
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First guess: Baryons (white dwarfs, brown dwarfs, neutron stars, jupiter-like planets, black holes, etc.)
Baryon Abundance
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Big Bang nucleosynthesis combined with cosmic microwave background determine
B h 2
0.024
B ~ 0.05
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But, we also know
M ~ 0.3, so most of the matter in the Universe is non-baryonic!
Fields and Sarkar, 2004
Cold Dark Matter and Structure Formation
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Observations of the large scale structure of our Universe can be compared to computer simulations
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Simulation results depend primarily on whether the dark matter is hot (relativistic) or cold (non-relativistic) when structures were formed
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Most of the Universe’s matter must be Cold Dark Matter
“The world is full of obvious thing which nobody by any chance ever observes.” -Sherlock Holmes
What do we know about dark matter?
Ask An Astrophysicist:
A Great Deal!
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)
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,…
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A virtual zoo of dark matter candidates have been proposed over the years. 100’s of viable candidates.
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Weakly Interacting Massive Particles (WIMPs) are a particularly attractive class of dark matter candidates.
The Thermal Abundance of a WIMP
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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)
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As Universe cools, number density of X becomes Boltzman suppressed
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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
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For a particle with weak scale interactions, freeze-out occurs at a temperature, T~M X /20
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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
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For a particle with weak scale interactions, freeze-out occurs at a temperature, T~M X /20
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With weak scale interactions, freeze out leads to a density of X particles of
~1 Automatically generates observed relic density!!!
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
Why Supersymmetry?
Not
introduced for dark matter
Why Supersymmetry?
Not
introduced for dark matter Higgs mass stability
Supersymmetry and the Mass of the Higgs Boson
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Electroweak precision observables indicate the presence of a light Higgs boson (around ~100 GeV)
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Large contributions to the Higgs mass come from particle loops:
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Without SUSY,
~ M GUT or ~ M Planck
ultra-heavy Higgs
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With TeV scale SUSY, boson and fermion loops nearly cancel
light Higgs
Why Supersymmetry?
Not
introduced for dark matter Higgs mass stability Grand Unification
Supersymmetry and Grand Unification
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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
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In the Standard Model, couplings become similar, but not equal
Supersymmetry and Grand Unification
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With Supersymmetry, the three forces can unify at a single scale
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
• •
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
• •
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
• •
The Lightest Supersymmetric Particle Dark matter candidates must be electrically neutral, not colored Mix to form 4 Possibilities: neutralinos photino Zino (neutral) higgsinos sneutrinos gravitino axino Ruled out by direct detection Do not naturally generate the observed dark matter density
How To Search For A WIMP
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Direct Detection
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Indirect Detection
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Colliders
Direct Detection
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Underground experiments hope to detect recoils of dark matter particles elastically scattering off of their detectors
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Prospects depend on the WIMP’s elastic scattering cross section with nuclei
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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:
h,H q q q q
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Cross section depends on numerous SUSY parameters: neutralino mass and composition, tan
, squark masses and mixings, Higgs masses and mixings SUSY Models
Direct Detection
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Current Status Zeplin, Edelweiss DAMA CDMS Supersymmetric Models
Direct Detection
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Near-Future Prospects Zeplin, Edelweiss DAMA CDMS Supersymmetric Models CDMS, Edelweiss Projections
Direct Detection
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Long-Term Prospects Zeplin, Edelweiss DAMA CDMS Supersymmetric Models Super-CDMS, Zeplin-Max
Indirect Detection
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Attempt to observe annihilation products of dark matter annihilating in halo, or elsewhere
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Prospects depend on both the characteristics of the dark matter particle and its distribution in the halo
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Gamma-rays, neutrinos, positrons, anti-protons and anti deuterons each provide a potentially viable channel for the detection of dark matter
Indirect Detection: Anti-Matter
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Matter and anti-matter generated equally in dark matter annihilations (unlike other processes)
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Cosmic positron, anti-proton and anti-deuteron spectrum may contain signatures of particle dark matter
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Upcoming experiments (PAMELA, AMS-02) will measure the cosmic anti-matter spectrum with much greater precision, and at much higher energies
Indirect Detection: Positrons
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Positrons produced through a range of dark matter annihilation channels: (decays of heavy quarks, heavy leptons, gauge bosons, etc.)
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Positrons move under influence of galactic magnetic fields
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Energy losses through inverse compton and synchotron scattering with starlight, CMB
Indirect Detection: Positrons
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Determine positron spectrum at Earth by solving diffusion equation: Inputs: Diffusion Constant
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Diffusion constant
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Energy loss rate
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Annihilation cross section/modes
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Halo profile (inhomogeneities?)
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Boundary conditions
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Dark matter mass Energy Loss Rate Source Term
Indirect Detection: Positrons
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Reduce systematics by studying the “positron fraction”
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When plotted this way, HEAT experiment observes a significant excess
Indirect Detection: Positrons Supersymmetric (neutralino) origin of positron excess?
-Spectrum generated by annihilating neutralinos can fit the HEAT data
Indirect Detection: Positrons Supersymmetric (neutralino) origin of positron excess?
-Spectrum generated by annihilating neutralinos can fit the HEAT data -Normalization is another issue
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 (~10 4 - 10 8
Unlikely at 10 -4 level M
) Hooper, J. Taylor and J. Silk, PRD (hep-ph/0312076) H. Zhao, J. Taylor, J. Silk and Hooper (hep-ph/0508215)
Indirect Detection: Positrons Where does this leave us?
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Future cosmic positron experiments hold great promise
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PAMELA satellite, planned to be launched in 2006
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AMS-02, planned for deployment onboard the ISS (???)
Indirect Detection: Positrons With a “HEAT sized” signal:
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Dramatic signal for either PAMELA or AMS-02
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Clear, easily identifiable signature of dark matter Hooper and J. Silk, PRD (hep-ph/0409104)
Indirect Detection: Positrons With a smaller signal:
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More difficult for PAMELA or AMS-02
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Still one of the most promising dark matter search techniques Hooper and J. Silk, PRD (hep-ph/0409104)
Indirect Detection: Positrons Prospects for Neutralino Dark Matter:
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AMS-02 can detect a thermal (s-wave) relic up to ~200 GeV, for any boost factor, and all likely annihilation modes
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For modest boost factor of ~ 5, AMS-02 can detect dark matter as heavy as ~1 TeV
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PAMELA, with modest boost factors, can reach masses of ~250 GeV
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Non-thermal scenarios (AMSB, etc), can be easily tested Value for thermal abundance Hooper and J. Silk, PRD (hep-ph/0409104)
Indirect Detection: Neutrinos
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WIMPs elastically scatter with massive bodies (Sun)
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Captured at a rate ~ 10 18 s -1 (
p /10 -8 pb) (100 GeV/m
) 2
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Over billions of years, annihilation/capture rates equilibrate
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Annihilation products are absorbed, except for neutrinos
Indirect Detection: Neutrinos The IceCube Neutrino Telescope
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Full cubic kilometer instrumented volume
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Technology proven with predecessor, AMANDA
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First string of detectors deployed in 2004/2005, 8 more strings deployed in 2005/2006 (80 in total)
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Sensitive to muon neutrinos above ~ 100 GeV
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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
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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
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Direct detection constraints on spin-dependent scattering are still very weak Spin-Independent Spin-Dependent
Indirect Detection: Neutrinos What Kind of Neutralino Has a Large Spin-Dependent Coupling?
Z q q q q
|f H1 | 2 - |f H2 | 2 Always Small Substantial Higgsino Component Needed
Indirect Detection: Neutrinos What Kind of Neutralino Has a Large Spin-Dependent Couplings?
F. Halzen and Hooper (hep-ph/0510048)
Indirect Detection: Gamma-Rays Advantages of Gamma-Rays
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Propagate undeflected (point sources possible)
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Propagate without energy loss (spectral information)
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Distinctive spectral features (lines), provide potential “smoking gun”
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Wide range of experimental technology (ACTs, satellite-based) Disadvantages of Gamma-Rays
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Flux depends critically on poorly known inner halo profiles
predictions dramatically vary from model to model
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Astrophysical backgrounds
Indirect Detection: Gamma-Rays The Galactic Center Region
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Likely to be the brightest source of dark matter annihilation radiation
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Detected in ~TeV gamma-rays by three ACTs: Cangaroo-II, Whipple and HESS
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Possible evidence for dark matter?
Indirect Detection: Gamma-Rays The Cangaroo-II Observation
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Consistent with WIMP in ~1-4 TeV mass range
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Roughly consistent with Whipple/Veritas Hooper, Perez, Silk, Ferrer and Sarkar, JCAP, astro-ph/0404205
Indirect Detection: Gamma-Rays The Cangaroo-II Observation
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Consistent with WIMP in ~1-4 TeV mass range
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Roughly consistent with Whipple/Veritas The HESS Obsevation
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Superior telescope
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Inconsistent with Cangaroo-II
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Extends at least to ~10 TeV
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WIMP of ~10-40 TeV mass needed D. Horns, PLB, astro-ph/0408192
Indirect Detection: Gamma-Rays Can A Neutralino Be As Heavy As 10-40 TeV?
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Very heavy neutralinos tend to overclose the Universe
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Neutralinos heavier than a few TeV require fine tuning (through coannihilations) to evade too much relic density (S. Profumo, hep-ph/0508628)
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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)
Indirect Detection: Gamma-Rays Can A Neutralino Be As Heavy As 10-40 TeV?
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Very heavy neutralinos tend to overclose the Universe
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Neutralinos heavier than a few TeV require fine tuning (through coannihilations) to evade too much relic density (S. Profumo, hep-ph/0508628)
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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
Indirect Detection: Gamma-Rays Messenger Sector Dark Matter
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In Gauge Mediated SUSY Breaking (GMSB) models, SUSY is broken in ~100 TeV sector
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LSP is a light gravitino (1-10 eV), poor DM candidate
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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)
Indirect Detection: Gamma-Rays Messenger Sector Dark Matter
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Gamma-ray spectrum (marginally) consistent with HESS data
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Normalization requires highly cuspy, compressed, or spiked halo profile
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With further HESS observation of region, dark matter hypothesis should be conclusively tested
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Source appears increasingly likely to be of an astrophysical origin Hooper and J. March-Russell, PLB (hep-ph/0412048)
Astrophysical Origin of Galactic Center Source?
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A region rich in extreme astrophysical objects
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Particle acceleration associated with supermassive black hole?
Aharonian and Neronov (astro-ph/0408303), Atoyan and Dermer (astro-ph/0410243)
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Nearby Supernova Remnant to close to rule out
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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
Indirect Detection: Gamma-Rays Dwarf Spheriodal Galaxies
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Several very high mass-to-light dwarf galaxies in Milky Way (Draco, Sagittarius, etc.)
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Little is known for certain about the halo profiles of such objects
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For example, draco mass estimates range from 10 7 to 10 10 solar masses
broad range of predictions for annihilation rate/gamma-ray flux
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May provide several very bright sources of dark matter annihilation radiation… or very, very little
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Detection of Draco by CACTUS experiment??? (Bergstrom & Hooper, hep-ph/0512317; Profumo & Kamionkowski, astro-ph/0601249)
How To Search For A WIMP: Colliders
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If m DM ~ m EW (along with associated particles), discovery likely at LHC and/or Tevatron
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Strong constraints from LEP data
Supersymmetry At The Tevatron
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Most promising channel is through neutralino-chargino production For example,
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Tevatron searches for light squarks and gluinos are also interesting
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Tevatron SUSY searches only possible if superpartners are rather light
Supersymmetry At The LHC
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Squarks and gluinos will be produced prolificly at the LHC (probably discovered within first month of running)
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Squarks/gluinos decay to leptons+jets+missing energy (LSPs)
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Lightest neutralino mass to be measured to ~10% precision
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But is it dark matter?
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Calculated relic density should be compared to CDM density
Putting It All Together
Summary
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Very exciting prospects exist for direct, indirect and collider searches for dark matter
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Cosmic anti-matter searches will be sensitive to thermally produced (s-wave) WIMPs up to hundreds of GeV (PAMELA) or ~1 TeV (AMS-02)
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Kilometer scale neutrino telescopes (IceCube, KM3) will be capable of detecting mixed gaugino-higgsino neutralinos
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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
The Cork Is Still In the Champagne Bottle…
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Furthermore…
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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)
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Collider searches (LHC, Tevatron) are exceedingly likely to discover Supersymmetry or whatever other new physics is associated with the electroweak scale