topics on dark matter annihilation
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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 - PowerPoint PPT PresentationTRANSCRIPT
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– EGRET spectrum update
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?
Positron Excess from DM Annihilation
• This is a classic subject.– Tylka (1989); Turner & Wilczek (1990); Kamionko
wski & 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 pa
rameters
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Direct Annihilation to e+e- • Positrons
lose their energy as they propagate through the magnetized interstellar medium.
Hooper & Silk (2005)
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Decays of Ws, Zs• No sharp fe
atures exist in this case because positrons are secondary products.
Hooper & Silk (2005)
mDM=100 GeV
300 GeV
600 GeV
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 part
icles around us?• Possible, but not very likely (theoretically)…
• AMS-02’s data will contribute to this subject significantly.
(Hooper arXiv:0710.2062)
AMS-02 Forecast
• Blue: AMS-02; Red: PAMELA
Hooper & Silk (2005)
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Somewhat More Realistic
• These values are below the current data.
Hooper & Silk (2005)
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Microwave SkyWMAP 94GHz
Gamma-ray Sky
Deciphering Gamma-ray Sky• AstrophysicalAstrophysical: Galactic vs Extra-galactic
– Galactic origin (diffuse)• E.g., Decay of neutral pions produced by cosmic-rays interacting with the i
nterstellar 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
“HST” for charged particles, and “WMAP” for gamma-rays?
WMAP 94GHz
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
“WMAP Haze”
• The WMAP haze is consistent with synchrotron from relativistic electrons that are produced by DM annihilation.
Finkbeiner (2004)
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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)
Finkbeiner (2004); Hooper, Finkbeiner & Dobler (2007)
v: A Closer Look
• Both mass and v of DM inferred from the haze are reasonable… Neutralinos?
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bW
Z
e
Required for cosmic DM density
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
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Predicted Signals from G.C.
• Errors: GLAST forecast• Data Points: HESS measurements of G.C.
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Hooper, Zaharijas, Finkbeiner & Dobler (2007)
Bit Away from G.C. (0.3 to 0.5deg)
• Much lower astrophysical background.
Hooper, Zaharijas, Finkbeiner & Dobler (2007)
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Extra-galactic Background
• Is the “bump” at ~10 GeV real?
• The issue: the amplitude of the bump depends on how you remove the Galactic contribution…
Ando et al. (2007)
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.
De Boer et al. Result
• Inclusion of the Galactic DM annihilation does affect the background level somewhat, but (fortunately) not very much.
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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)
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Summary• Positron Excess
– This classic problem is still there.– DM explanation is possible -- AMS-02’s contributio
n 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 A
MS-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!