1. Topics on Dark Matter Annihilation
Eiichiro Komatsu
University of Texas at Austin
AMS
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. Direct Annihilation to e+e-
Hooper & Silk (2005)
Positrons lose their energy as they propagate through the magnetized interstellar medium.

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

7. The Current State of Affairs
(Hooper arXiv: )
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. Somewhat More Realistic
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. WMAP Haze: Implications for DM
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~3x10-26 cm3/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 W Z   e
Both mass and v of DM inferred from the haze are reasonable… Neutralinos?

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

20. Bit Away from G.C. (0.3 to 0.5deg)
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: ) 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 WMAP Haze Extra-galactic background
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!