Two phases of WIMP dark matter annihilation in the First Stars
Topics on Dark Matter Annihilation
description
Transcript of 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– 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
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
Direct Annihilation to e+e- • Positrons
lose their energy as they propagate through the magnetized interstellar medium.
Hooper & Silk (2005)
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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)
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
Somewhat More Realistic
• These values are below the current data.
Hooper & Silk (2005)
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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)
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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?
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
Predicted Signals from G.C.
• Errors: GLAST forecast• Data Points: HESS measurements of G.C.
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
Hooper, Zaharijas, Finkbeiner & Dobler (2007)
Bit Away from G.C. (0.3 to 0.5deg)
• Much lower astrophysical background.
Hooper, Zaharijas, Finkbeiner & Dobler (2007)
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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.
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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)
QuickTime˛ Ç∆TIFFÅià≥èkǻǵÅj êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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!