Topics on Dark Matter Annihil ation

(1)

Topics on Dark Matter Annihil ation

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 An nihilation

– EGRET spectrum update

(3)

Positron Excess:

AMS-01’s Result

• The positron excess at >1 0 GeV is still there.

• The origin of the excess is still unknown.

• DM Annihilati on?

(4)

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 dec ays of the products of DM annihilation, such a s

– Gauge bosons, quarks, leptons

– The dominant modes depend on the DM model pa rameters

(5)

QuickTime˛ Ç∆

TIFFÅià≥èkÇ»ÇµÅj êLí£ÉvÉçÉOÉâÉÄ

Ç™Ç±ÇÃÉsÉNÉ`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)

(6)

QuickTime˛ Ç∆

Decays of Ws, Zs

• No sharp fe atures exist i n this case b ecause posi trons are s econdary p roducts.

m_DM=100 GeV 300 GeV

600 GeV

(7)

The Current State of Affairs

• Theoretical calculations show that the measur ed positron excess is “too large” (by a factor o f ~50) to be produced by annihilation of smoo th 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 si gnificantly.

(Hooper arXiv:0710.2062)

(8)

AMS-02 Forecast

• Blue: AMS-02; Red: PAMELA

QuickTime˛ Ç∆

Ç™Ç±ÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇﬂÇ…ÇÕïKóvÇ≈Ç∑ÅB QuickTime˛ Ç∆

(9)

Somewhat More Realistic

• These values are below the current data.

QuickTime˛ Ç∆

Ç™Ç±ÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇﬂÇ…ÇÕïKóvÇ≈Ç∑ÅB QuickTime˛ Ç∆

(10)

Microwave Sky

WMAP 94GHz

(11)

Gamma-ray Sky

(12)

Deciphering Gamma-ray Sky

• Astrophysical: Galactic vs Extra-galacticAstrophysical

– 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

(13)

“HST” for charged particles, an d “WMAP” for gamma-rays?

WMAP 94GHz

(14)

New Evidence From WMAP?

• Doug Finkbeiner at Harvard claims that there is a significant excess of synchrotr on 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)

“WMAP Haze”

• The WMAP haze is

consistent with synchrotron

from relativistic electrons that are produced by DM

annihilation.

Finkbeiner (2004)

QuickTime˛ Ç∆

(16)

WMAP Haze: Implications for DM

• The inferred DM density profile in the Gala ctic 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 pr esent-day cosmic DM density)

• The required DM particle mass is m_DM~10 0 GeV to ~TeV (in agreement with neutral inos)

Finkbeiner (2004); Hooper, Finkbeiner & Dobler (2007)

(17)

v: A Closer Look

• Both mass and v of DM inferred from t he haze are reasonable… Neutralinos?

QuickTime˛ Ç∆

b W

Z



 e

Required for cosmic DM density

(18)

How About Gamma-rays?

• The haze is produced by relativistic elec trons, which could be the product of DM annihilation.

• How about other products, like gamma-r ays?

Here

(19)

QuickTime˛ Ç∆

Predicted Signals from G.C.

• Errors: GLAST forecast

QuickTime˛ Ç∆

Hooper, Zaharijas, Finkbeiner & Dobler (2007)

(20)

Bit Away from G.C. (0.3 to 0.5deg)

• Much lower astrophysical background.

Hooper, Zaharijas, Finkbeiner & Dobler (2007)

QuickTime˛ Ç∆

(21)

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)

(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 D M 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 ann ihilation does aff ect the backgrou nd level somewh at, but (fortunate ly) not very muc h.

QuickTime˛ Ç∆

(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)

QuickTime˛ Ç∆

(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 AM S-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!