Detecting Dark Matter In The Milky Way Workshop

1. Detecting Dark Matter In The Milky Way Workshop Dan Hooper Fermilab/University of Chicago Case Western Reserve University March 12-14, 2009

2. Things We Know About Dark Matter Current Status

3. Current Status

4. Evidence For Dark Matter • Galactic rotation curves • Gravitational lensing • Light element abundances • CMB anisotropies • Large scale structure • Etc…

5. Evidence For Dark Matter • Galactic rotation curves • Gravitational lensing • Light element abundances • CMB anisotropies • Large scale structure • Etc… -Cold, -Non-baryonic, -Collisionless

6. How Do We Find Out More? Current Status

7. How Do We Find Out More? Current Status (What Is The Dark Matter?)

8. WIMP Hunting • Direct Detection • Indirect Detection • Collider Searches

9. Direct Detection Experiments • Elastic scattering between WIMPs and target nuclei • In the past two years, we have seen an order of magnitude improvement in sensitivity Current Status ZEPLIN, CRESST, WARP, Edelweiss CDMS XENON

10. Current Status Near Future ZEPLIN, CRESST, WARP, Edelweiss Direct Detection Experiments CDMS XENON CDMS XENON-100

11. Current Status Near Future ZEPLIN, CRESST, WARP, Edelweiss Direct Detection Experiments CDMS XENON CDMS XENON-100 • The next step is the ton-scale: • LUX, Super-CDMS, DEAP-CLEAN…

12. Sensitivities are at ~10-43 cm2 and improving rapidly

13. Sensitivities are at ~10-43 cm2 and improving rapidly...-At what point should we expect a signal?-What do these limits tell us about the nature of dark matter?

14. Case Example: Dirac Fermion or Scalar WIMP with vector-like interactions (such as a heavy 4th generation neutrino, or a sneutrino) Coupling Needed To Acquire Measured Abundance WIMPs Ruled Out By Direct Detection    q Z Z q  q q This candidate and many others are already excluded by the null results of CDMS and XENON! Beltran, Hooper, Kolb, Krusberg, arXiv:0808.3384

15. Another Case Example: Majorana Fermion WIMP (such as a neutralino) • Neutralino elastic scattering is suppressed by the fact that they annihilate to heavy quarks (and leptons) and gauge/higgs bosons, none of which are present in nuclei • Elastic scattering is further suppressed if coannihilations or resonances play an important role in the early universe More Elusive WIMPs    Q,W,Z,H  Q, W,Z, H q q

16. Current direct detection experiments do not constrain a significant fraction of the likely SUSY parameter space • A significant fraction of the favored parameter space is near current constraints The Case of Neutralino Dark Matter REWSB Priors Flat tan Priors Focus Point Stau Coannihilation Light Higgs Pole B. Allanach and D. Hooper, arXiv:0806.1923

17.  WIMP Annihilation Typical final states include heavy fermions, gauge or Higgs bosons  The Indirect Detection of Dark Matter W- W+

18.  WIMP Annihilation Typical final states include heavy fermions, gauge or Higgs bosons Fragmentation/DecayAnnihilation products decay and/or fragment into combinations of electrons, protons, deuterium, neutrinos and gamma-rays  The Indirect Detection of Dark Matter W- q W+ q  e+ 0 p  

19.  WIMP Annihilation Typical final states include heavy fermions, gauge or Higgs bosons Fragmentation/DecayAnnihilation products decay and/or fragment into combinations of electrons, protons, deuterium, neutrinos and gamma-rays Synchrotron and Inverse Compton Relativistic electrons up-scatter starlight/CMB to MeV-GeV energies, and emit synchrotron photons via interactions with magnetic fields  The Indirect Detection of Dark Matter W- q W+ q  e+ 0 p    e+

20. Neutrinos from annihilations in the core of the Sun • Gamma Rays from annihilations in the galactic halo, near the galactic center, in dwarf galaxies, etc. • Positrons/Antiprotons from annihilations throughout the galactic halo • Synchrotron Radiation from electron/positron interactions with the magnetic fields of the inner galaxy The Indirect Detection of Dark Matter

21. (When it rains it pours) Pamela IceCube New Indirect Detection Results! Fermi/Glast

22. (When it rains it pours) Pamela IceCube New Indirect Detection Results! NEW MEASUREMENT! NEW LIMIT! Fermi/Glast FIRST RESULTS!

23. Charged Particle Astrophysics With Pamela • Major step forward in sensitivity to GeV-TeV cosmic ray electrons, positrons, protons, antiprotons, and light nuclei • Among other science goals, PAMELA hopes to identify or constrain dark matter annihilations in the Milky Way halo by measuring the cosmic positron and antiproton spectra

24. Pamela’s New Antiproton Measurement • Best measurement to date • Dramatically smaller error bars above ~1-10 GeV • The antiprotons detected by Pamela are consistent with being entirely from secondary production (byproduct of cosmic ray propagation) Pamela Collaboration, arXiv:0810.4994

25. Pamela’s New Positron Measurement Rapid climb above 10 GeV indicates the presence of a primary source of cosmic ray positrons! • Charge-dependent solar modulation important below 5-10 GeV! Astrophysical expectation (secondary production) Pamela Collaboration, arXiv:0810.4995

26. The New Cosmic Ray Electron Spectrum From ATIC • In a series of balloon flights, ATIC has measured an excess of cosmic ray electrons between 300 and 800 GeV (Nature, Nov. 21, 2008) • This requires a local source of cosmic ray electrons/positrons (within ~1 kpc) • If we extrapolate the Pamela positron fraction up to higher energies, the ATIC result approximately matches

27. WMAP and Energetic Electrons/Positrons • WMAP does not only detect CMB photons, but also a number of galactic foregrounds • GeV-TeV electrons emit hard synchrotron in the frequency range of WMAP Thermal Dust Soft Synchrotron (SNe) WMAP Free-Free

28. “The WMAP Haze” 22 GHz After known foregrounds are subtracted, an excess appears in the residual maps within the inner ~20 around the Galactic Center

29. Pamela, ATIC, and WMAP • Highly energetic electrons and positrons are surprisingly common both locally, and in the central kiloparsecs of the Milky Way • Not the product of any plausible propagation mechanism or other such effect (see P. Serpico, arXiv:0810.4846) • Constitutes the discovery of a bright source(s) of e+e- pairs with a very hard spectral index

30. Dark Matter as the Source of the Pamela, ATIC, and WMAP Signals • The distribution and spectrum of the WMAP haze are consistent with being of dark matter origin • The spectral features observed by Pamela and ATIC could also be generated by dark matter annihilations Cholis, Goodenough, Hooper, Simet, Weiner arXiv:0809.1683 Hall and Hooper, arXiv:0811.3362

31. Dark Matter as the Source of the Pamela, ATIC, and WMAP Signals • The distribution and spectrum of the WMAP haze are consistent with being of dark matter origin • The spectral features observed by Pamela and ATIC could also be generated by dark matter annihilations Cholis, Goodenough, Hooper, Simet, Weiner arXiv:0809.1683 But not necessarily easily… Hall and Hooper, arXiv:0811.3362

32. Dark Matter as the Source of the Pamela and ATIC Signals Challenges Faced Include: Very hard spectrum Requires a very high annihilation rate 3) Too many antiprotons, gamma rays, synchrotron

33. Dark Matter as the Source of the Pamela and ATIC Signals Particle Physics Solutions:

34. Dark Matter as the Source of the Pamela and ATIC Signals Particle Physics Solutions: Very hard injection spectrum (a large fraction of annihilations to e+e-, +- or +-) Cholis, Goodenough, Hooper, Simet, Weiner arXiv:0809.1683

35. Dark Matter as the Source of the Pamela and ATIC Signals Particle Physics Solutions: Very hard injection spectrum (a large fraction of annihilations to e+e-, +- or +-) Annihilation rate dramatically increased by non-perturbative effects known as the “Sommerfeld Enhancement” -Very important for m<<mX and vX<<c (such as in the halo, where vx/c~10-3) SM X  X SM SM X   X SM Arkani-Hamed, Finkbeiner, Slatyer, Weiner, arXiv:0810.0713; Cirelli and Strumia, arXiv:0808.3867; Fox and Poppitz, arXiv:0811.0399

36. Dark Matter as the Source of the Pamela and ATIC Signals Astrophysical Solutions:

37. Dark Matter as the Source of the Pamela and ATIC Signals Astrophysical Solutions: More small-scale structure than expected (a “boost factor” of ~103)

38. Dark Matter as the Source of the Pamela and ATIC Signals Astrophysical Solutions: More small-scale structure than expected (a “boost factor” of ~103) A narrow diffusion region D. Hooper and J. Silk, PRD, hep-ph/04091040

39. Dark Matter as the Source of the Pamela and ATIC Signals Astrophysical Solutions: More small-scale structure than expected (a “boost factor” of ~103) A narrow diffusion region A large nearby clump of dark matter

40. A Nearby Clump of Dark Matter? • In the standard picture, WIMPs distributed throughout the halo contribute to the spectrum of cosmic ray electrons and positrons • Nearby sources produce a harder spectrum (less propagation) • Motion of clump hardens the spectrum further Hooper, A. Stebbins and K. Zurek, arXiv:0812.3202

41. A Nearby Clump of Dark Matter? A clump of neutralino dark matter ~1 kpc from the Solar System provides an excellent fit to Pamela and ATIC while also: • Evading constraints from antiproton, gamma ray, and synchrotron measurements • Providing a plausible scenario for generating the required very high annihilation rate Hooper, A. Stebbins and K. Zurek, arXiv:0812.3202

42. High-Energy Positrons From Nearby Pulsars • Rapidly spinning (~msec period) neutron stars, accelerate electrons to very high energies (power from slowing rotation - spindown) • Energies can exceed the pair production threshold • Very young pulsars (<10,000 years) are typically surrounded by a pulsar wind nebula, which can absorb energetic pairs • Most of the spindown power is expended in first ~105 years ~ Vela Pulsar (12,000 yrs old)

43. High-Energy Positrons From Nearby Pulsars Two promising candidates: • Geminga (157 pc away, 370,000 years old) • B0656+14 (290 pc, 110,000 years) B0656+14 Geminga A few percent of the total spindown energy is needed in high energy e+e- pairs Hooper, P. Blasi, P. Serpico, JCAP, arXiv:0810.1527

46. Where To Look For Dark Matter With Fermi? The Galactic Halo -High statistics -Requires detailed model of galactic backgrounds The Galactic Center -Brightest spot in the sky -Considerable astrophysical backgrounds Individual Subhalos -Unlikely detectable -Low backgrounds Extragalactic Background -High statistics -potentially difficult to identify Diemand, Kuhlen, Madau, APJ, astro-ph/0611370

47. Current Status Things We Need To Know Before We Can Learn More About Dark Matter

48. The Distribution Of Dark Matter At The Most Relevant Scales • Observations and simulations tell us a lot about how dark matter is distributed at very large scales, but less/little/nothing about: -The galactic center -Galactic substructure -Baryonic effects on inner profiles -The phase space density near the solar circle All very important inputs for direct and indirect searches!

49. The Backgrounds And Other Astrophysical Inputs For Indirect Dark Matter Searches? • The challenge in indirect detection is not only in observing dark matter annihilation products, but in separating them from astrophysical backgrounds Population studies, multi-wavelength studies, and input from other indirect, direct and/or LHC channels are all going to be essential if anyone is going to believe any indirect detection result!

50. The Backgrounds And Other Astrophysical Inputs For Indirect Dark Matter Searches? • Many astrophysical inputs which go into interpreting Pamela and other cosmic ray data are not very well known: -B fields/diffusion model -radiation fields -solar modulation -primary electron spectrum Need better measurements of cosmic ray nuclei, especially at high energies, and possibly better diffusion models (move beyond single zone models?)