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Astrophysical Experiments and Supersymmetry: Unraveling the Mystery of Dark Matter

This article explores the connections between astrophysical experiments and supersymmetry to gain insights into the nature of dark matter. It discusses the various candidates for dark matter, including WIMPs and the lightest neutralino, and highlights the potential for astrophysical measurements to determine the composition of dark matter particles. The article also touches upon the prospects of direct detection experiments and the current status and future projections in this field.

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Astrophysical Experiments and Supersymmetry: Unraveling the Mystery of Dark Matter

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  1. What Can We Learn About Supersymmetry From Astrophysical Experiments? Dan Hooper Particle Astrophysics Center Fermi National Laboratory dhooper@fnal.gov University of Oregon Cosmo/Astro Mini-Workshop May 22-26, 2006

  2. Based On: M. Carena, DH, P. Skands, hep-ph/0603180 F. Halzen, DH, hep-ph/0510048, PRD DH and Andrew Taylor (in preparation)

  3. 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 (compelling since the 1970’s) • White dwarfs, brown dwarfs, Jupiter-like planets, neutron stars, black holes, etc?

  4. The Dark Matter Density • WMAP best-fit LCDM model (for a flat Universe): • 73 % Dark energy (WL= 0.73) • 27 % Matter (Mh2 = 0.27) • h2  0.0076

  5. BaryonicAbundance • Big Bang nucleosynthesis combined with cosmic microwave background determine WBh2 0.024 • But, we also know WM~ 0.3, so most of the matter in the Universe is non-baryonic dark matter! Fields and Sarkar, 2004

  6. 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 Universe’s matter must be Cold Dark Matter

  7. “The world is full of obvious things which nobody by any chance ever observes.” -Sherlock Holmes

  8. 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. 100’s of viable candidates. Weakly Interacting Massive Particles (WIMPs) are a particularly attractive class of dark matter candidates.

  9. Supersymmetry • Introduces new bosons for fermions and vice versa • Elegant extension of the Standard Model • Natural solution to hierarchy problem (stabilizes quadradic divergences to Higgs mass) • Restores unification of couplings • Requirement of proton stability implies the stability of the Lightest Supersymmetric Particle (LSP) by the virtue of R-parity • The lightest neutralino is among the most natural possibilities for the LSP

  10. The Lightest Neutralino Higgsinos Bino Wino • Properties of the lightest neutralino can vary wildly depending on its composition • The composition of the lightest neutralino will likely not be determined at the LHC • Annihilation and elastic scattering cross sections with nucleons can vary over many orders of magnitude depending on LSP’s composition (and sparticle spectrum, tan , etc.) • By including astrophysical measurements with LHC data, it may be possible to determine the composition of the lightest neutralino

  11. Can Astrophysics Measure ?

  12. Supersymmetry At The Tevatron • Most promising channel is through neutralino-chargino production • For example, • For the case of light mA and large tan, heavy MSSM higgs bosons (A/H) are observable • Tevatron searches for light squarks and gluinos are also interesting • Tevatron SUSY searches only possible if superpartners are rather light

  13. Supersymmetry At The LHC • Squarks and gluinos will be produced prolifically at the LHC • Squarks/gluinos decay to distinctive combinations of leptons, jets and missing energy (LSPs) • Capable of discoverying squarks/gluinos as heavy as ~3 TeV

  14. Supersymmetry At The LHC • Squarks/gluinos decay to leptons+jets+missing energy (LSPs) • By studying decay kinematics, lightest neutralino mass to be measured to ~10% precision • Masses of sleptons and heavier neutralinos may also be determined if sufficiently light • But what is the nature of the LSP? • Is it dark matter?

  15. Astrophysical Dark Matter Experiments • Direct Detection • - Momentum transfer to detector • through elastic scattering • Indirect Detection • - Observation of annihilation • products (, e+, p, , etc.)

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

  17. 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

  18. Direct Detection • Current Status Zeplin, Edelweiss DAMA CDMS Supersymmetric Models

  19. Direct Detection • Near-Future Prospects Zeplin, Edelweiss DAMA CDMS Supersymmetric Models CDMS, Edelweiss Projections

  20. Direct Detection • Long-Term Prospects Zeplin, Edelweiss DAMA CDMS Supersymmetric Models Super-CDMS, Zeplin-Max

  21. Direct Detection • But what does direct detection tell us? • Models with large cross sections are dominated by Higgs exchange, couplings to b, s quarks • Squark exchange contribution substantial only below ~10-8 pb • Leads to correlation between neutralino composition, tan , mA and the elastic scattering rate

  22. Searches For Heavy MSSM Higgs at the Tevatron • Heavy (A/H) MSSM higgs searches at the Tevatron/LHC are most sensitive for models with small mA and large tanp p  A/H X + - X p p  A/H bb bb bb

  23. Searches For Heavy MSSM Higgs at the Tevatron • Projected Reach Both depend on tan, mA

  24. Direct Detection and Collider Searches Current CDMS Limit For a wide range of M2 and , much stronger current limits on tan, mA from CDMS than from the Tevatron M. Carena, Hooper, P. Skands, hep-ph/0603180

  25. Direct Detection and Collider Searches 3 discovery reach, 4 fb-1 Projected 2007 CDMS Limit (assuming no detection) Limits from CDMS imply heavy Higgs (H/A) is beyond the reach of the Tevatron, unless LSP has a very small higgsino fraction (>>M2) M. Carena, Hooper, P. Skands, hep-ph/0603180

  26. Direct Detection and Collider Searches Constrained heavy Higgs (A/H) discovery potential at the Tevatron (4 pb-1) H/A discovery (3) not possible given current CDMS limits H/A discovery (3) not possible given projected 2007 CDMS limits (assuming no detection) M. Carena, Hooper, P. Skands, hep-ph/0603180

  27. 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

  28. 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

  29. Indirect Detection: Neutrinos • Neutrino flux depends on the capture rate, which is in turn tied to the neutralino’s elastic scattering cross section • Direct detection limits impact rates anticipated in neutrino telescopes

  30. Indirect Detection: Neutrinos • Neutralinos 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

  31. Indirect Detection: Neutrinos What Kind of Neutralino Has a Large Spin-Dependent Coupling?  Z q q q q q q Always Small  |fH1|2 - |fH2|2 Substantial Higgsino Component Needed

  32. Indirect Detection: Neutrinos What Kind of Neutralino Has a Large Spin-Dependent Coupling? High Neutrino Rates Hooper and A. Taylor; F. Halzen and Hooper (hep-ph/0510048)

  33. Indirect Detection: Neutrinos • Rates complicated by competing scalar and axial vector scattering Current CDMS Constraint Hooper and A. Taylor; F. Halzen and Hooper (hep-ph/0510048)

  34. Indirect Detection: Neutrinos • Rates complicated by competing scalar and axial vector scattering • Future bounds by CDMS will simplify neutrino rate considerably 100 Times Stronger Constraint Current CDMS Constraint High Neutrino Rates Hooper and A. Taylor; F. Halzen and Hooper (hep-ph/0510048)

  35. 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 • Unknown astrophysical backgrounds

  36. 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 four ACTs: • Cangaroo-II, Whipple, HESS and MAGIC • Possible evidence for dark matter?

  37. 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

  38. 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

  39. Indirect Detection: Gamma-Rays Can A Neutralino Be As Heavy As 10-40 TeV? • Very heavy neutralinos tend to overclose the Universe • Largest annihilation cross sections (lowest relic abundance) are found for Wino-like or Higgsino-like neutralinos • h2~0.1 for ~1 TeV Higgsino, or ~3 TeV Wino • Significantly larger masses are possible only if coannihilations are carefully arranged (for example, S. Profumo, hep-ph/0508628)

  40. Indirect Detection: Gamma-Rays Can A Neutralino Be As Heavy As 10-40 TeV? • Electroweak precision observables indicate the presence of a light higgs boson (near the EW scale) • Large contributions to the higgs mass come from particle loops: • In unbroken SUSY, boson and fermion loops exactly cancel • If mSUSY >> mHiggs , extreme fine tuning required • mSUSY below ~1 TeV is strongly preferred

  41. 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 • Generated gamma-ray spectrum not inconsistent with HESS/MAGIC source Dimopolous, Giudice, Pomarol; Han, Hemfling; Han, Marfatia, Zhang; Hooper and March-Russell, PLB (hep-ph/0412048)

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

  43. 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)

  44. Indirect Detection: Gamma-Rays • What Does the Gamma-Ray Spectrum Tell Us? • Most annihilation modes generate very similar spectra • +- mode is the most distinctive, although still not identifiable with planned experiments (GLAST, etc.) • Neutralino mass and annihilation cross section may be roughly extracted

  45. Indirect Detection: Gamma-Rays • What Does the Gamma-Ray Spectrum Tell Us? • At loop level, neutralinos annihilate to  and Z final states • Distinctive spectral line features • If bright enough, fraction of neutralino annihilations to lines can be measured

  46. Indirect Detection: Gamma-Rays • What Does the Gamma-Ray Spectrum Tell Us? • Chargino-W+/- loop diagrams provide largest contributions in most models • Cross sections largest for higgsino-like (or wino-like) neutralinos • Knowledge of squark masses makes this correlation more powerful A. Taylor, Hooper, in preparation

  47. Indirect Detection: Positrons • Gamma-ray observations can tell us the fraction of neutralino annihilation to various modes (, Z), but cannot measure the total cross section • Positron spectrum generated in neutralino annihilations is dominated by local dark matter distribution (within a few kpc) • Considerably less uncertainty in the local density than the density of inner halo profiles • Cosmic positron measurements can roughly measure the neutralino’s annihilation cross section

  48. Indirect Detection: Positrons • Positrons produced through a range of neutralino 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

  49. Indirect Detection: Positrons • Determine positron spectrum at Earth by solving diffusion equation: Energy Loss Rate Diffusion Constant • Inputs: • Diffusion constant • Energy loss rate • Annihilation cross section/modes • Halo profile (inhomogeneities?) • Boundary conditions • Neutralino mass Source Term

  50. Indirect Detection: Positrons • The HEAT Excess(?) • The HEAT balloon flights have measured an excess in the cosmic positron fraction between 5-30 GeV, although considerable ambiguities exist • Neutralinos can generate the observed spectral shape, but requires an annihilation rate a factor of ~50 or more above the rate expected for a thermal relic and a homogeneous dark matter distribution

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