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Topics on Dark Matter Annihilation

Topics on Dark Matter Annihilation. Eiichiro Komatsu University of Texas at Austin AMS Meeting@JSC October 22, 2007. Three Topics. The Positron Excess DM Annihilation? DM Annihilation in the Galactic Center New evidence? WMAP “Haze” Extra-galactic Gamma-rays from DM Annihilation

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Topics on Dark Matter Annihilation

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  1. Topics on Dark Matter Annihilation Eiichiro Komatsu University of Texas at Austin AMS Meeting@JSC October 22, 2007

  2. Three Topics • The Positron Excess • DM Annihilation? • DM Annihilation in the Galactic Center • New evidence? WMAP “Haze” • Extra-galactic Gamma-rays from DM Annihilation • EGRET spectrum update

  3. Positron Excess:AMS-01’s Result • The positron excess at >10 GeV is still there. • The origin of the excess is still unknown. • DM Annihilation?

  4. Positron Excess from DM Annihilation • This is a classic subject. • Tylka (1989); Turner & Wilczek (1990); Kamionkowski & Turner (1991); many others • The main idea: positrons are produced by decays of the products of DM annihilation, such as • Gauge bosons, quarks, leptons • The dominant modes depend on the DM model parameters

  5. Hooper & Silk (2005) Direct Annihilation to e+e- • Positrons lose their energy as they propagate through the magnetized interstellar medium.

  6. Hooper & Silk (2005) Decays of Ws, Zs • No sharp features exist in this case because positrons are secondary products. mDM=100 GeV 300 GeV 600 GeV

  7. (Hooper arXiv:0710.2062) The Current State of Affairs • Theoretical calculations show that the measured positron excess is “too large” (by a factor of ~50) to be produced by annihilation of smooth dark matter distribution around us (within a few kpc). • Are there (yet unknown) concentrations of DM particles around us? • Possible, but not very likely (theoretically)… • AMS-02’s data will contribute to this subject significantly.

  8. Hooper & Silk (2005) AMS-02 Forecast • Blue: AMS-02; Red: PAMELA

  9. Hooper & Silk (2005) Somewhat More Realistic • These values are below the current data.

  10. Microwave Sky WMAP 94GHz

  11. Gamma-ray Sky

  12. Deciphering Gamma-ray Sky • Astrophysical: Galactic vs Extra-galactic • Galactic origin (diffuse) • E.g., Decay of neutral pions produced by cosmic-rays interacting with the interstellar medium. • Extra-galactic origin (discrete sources) • Active Galactic Nuclei (AGNs) • Blazars • Gamma-ray bursts • Exotic: Galactic vs Extra-galactic • Galactic Origin • Dark matter annihilation in the Galactic Center • Dark matter annihilation in the sub-halos within the Galaxy • Extra-galactic Origin • Dark matter annihilation in the other galaxies

  13. “HST” for charged particles, and “WMAP” for gamma-rays? WMAP 94GHz

  14. New Evidence From WMAP? • Doug Finkbeiner at Harvard claims that there is a significant excess of synchrotron emission in the WMAP’s microwave data in the inner (1-2 kpc) region of the Galactic Center. • He calls this the WMAP “haze.” Here

  15. Finkbeiner (2004) “WMAP Haze” • The WMAP haze is consistent with synchrotron from relativistic electrons that are produced by DM annihilation.

  16. Finkbeiner (2004); Hooper, Finkbeiner & Dobler (2007) WMAP Haze: Implications for DM • The inferred DM density profile in the Galactic Center is ~r-1.2(in agreement with N-body simulations) • The required annihilation cross section is v~3x10-26cm3/s (in agreement with the present-day cosmic DM density) • The required DM particle mass is mDM~100 GeV to ~TeV (in agreement with neutralinos)

  17. v: A Closer Look Required for cosmic DM density b • Both mass and v of DM inferred from the haze are reasonable… Neutralinos? W Z   e

  18. How About Gamma-rays? • The haze is produced by relativistic electrons, which could be the product of DM annihilation. • How about other products, like gamma-rays? Here

  19. Hooper, Zaharijas, Finkbeiner & Dobler (2007) Predicted Signals from G.C. • Errors: GLAST forecast • Data Points: HESS measurements of G.C.

  20. Hooper, Zaharijas, Finkbeiner & Dobler (2007) Bit Away from G.C. (0.3 to 0.5deg) • Much lower astrophysical background.

  21. Extra-galactic Background Ando et al. (2007) • Is the “bump” at ~10 GeV real? • The issue: the amplitude of the bump depends on how you remove the Galactic contribution…

  22. De Boer et al. take this very seriously • De Boer et al. (arXiv:0705.0094) report on a “new determination” of the extra-galactic diffuse gamma-ray background. • A new component: they now include DM annihilation in the Galactic model, and subtract it for a better determination of the true background light.

  23. De Boer et al. Result • Inclusion of the Galactic DM annihilation does affect the background level somewhat, but (fortunately) not very much.

  24. De Boer et al.’s favorite model • This is the limitation of having only one piece of information: energy spectrum. • We need anisotropy data! (Ando&Komatsu 2006)

  25. Summary • Positron Excess • This classic problem is still there. • DM explanation is possible -- AMS-02’s contribution will be very important. • WMAP Haze • Needs to be confirmed by Planck (European CMB mission to be launched next year) • If it is due to DM annihilation, GLAST (as well as AMS-02?) would be able to see gamma-rays from G.C. • Extra-galactic background • This topic is getting hotter than ever. • We need more information, like anisotropy!

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