Dark matter annihilation and detection

X.J. Bi (IHEP)

2006.8.28

Outline

• Annihilation signals from the subhalos and the detection.

• GeV excess of diffuse gamma by EGRET and its possible explanation.

• Positron excess of HEAT and its possible explanation.

• An interesting dark matter model which predicts a heavy charged stable particle.

Subhalos in the MW halo • The DM annihilation flux is pro

portional to the DM density square

• A wealth of subhalos exist due to high resolution simulations.

Moore et al

2v

The first generation object

Diemand, Moore & Stadel, 2005:• Depending on the nature of

the dark matter: for neutralino-like dark matter, the first structures are mini-halos of 10-6 M⊙.

• There would be zillions of them surviving and making up a sizeable fraction of the dark matter halo.

• The dark matter detection schemes may be quite different!

-rays from the subhalos

Reed et al, MNRAS357,82(2004) -rays from subhalos-rays from subhalos

-rays from smooth bkg-rays from smooth bkg

source

sun GC

Statistical results

•The curves are due to different author’s simulations.

•The threshold is taken as 100 GeV.

•The susy factor is taken an optimistic value for neutralino mass between 500 GeV and 1TeV.

•Results are within the field of view of ARGO.

Instruments with large field of view and their

sensitivities

• GLAST

• ARGO/HAWC

Complementary capabilities

ground-based space-based ACT EAS Pair angular resolution good fair good duty cycle low high high area large large small field of view small large large+

can reorient energy resolution good fair good, with smaller systematic

uncertainties

Gamma ray detection from DM annihilation

my estimateHAWC~0.04ICRAB

Sensitivity at ARGO（ 95％ C.L.）

Diffuse gamma rays of the MW

• COS-B and EGRET (20keV~30GeV) observed diffuse gamma rays, measured its spectra.

• Diffuse emission comes from nucleon-gas interaction, electron inverse Compton and bremsstrahlung. Different process dominant different parts of spectrum, therefore the large scale nucleon, electron components can be revealed by diffuse gamma.

GeV excess of spectrum• Based on local s

pectrum gives consistent gamma in 30 MeV~500 MeV, outside there is excess.

• Harder proton spectrum explain diffuse gamma, however inconsistent with antiproton and position measurements.

• Hard proton or electron injection index

Contribution from DM

Fit the spectrum

• B~100

• Fi,j -----

Enhancement by substructures

Adjust the propagation parameters

With and without subhalos

dlrsol

mo )(..

2cos

Calculate cosmic rays

• Adjust the propagation parameter to satisfy all the observation data and at the same time satisfy the egret data after adding the dark matter contribution

Results of different regions

HEAT and positron excess• HEAT fou

nd a positron excess at ~10 GeV

B~100-1000

Enhancement by subhalos

• The average density (for annihilation) is improved with subhalos.

• The corresponding positron flux is improved.

Result • The positron fraction can be explained still

need a boost factor of about 2~3

Uncertainties in positron flux• Large uncertainties from propagation

• Uncertainties by the realization of the subhalos distribution.

Unified model of dark matter and dark energy

• Possible candidates of dark energy are the cosmological constant or a scalar field --- the quintessence field (a dynamical fundamental scalar field).

• The motivation is to build a unified model of dark matter and dark energy in the framework of supersymmetry.

• requiring a shift symmetry of the system, the quintessence is always kept light and the potential is not changed by quantum effects. If is the LSP, it is stable and forms DM.

QiQQ q

~),(ˆ

Q~

CQQ

Shift symmetry and interaction• To keep the shift symmetry the quintesssence fiel

d can only coupled with matter field derivatively. We consider the following interactions and derive their supersymmetric form:

FQFM

c

plQ

~L

FQ

Q~~ 5

~~ L

..|ˆ 2 cheQc gV

L iCQQ ˆˆ

quintessinoquintessinoSMSM

101066

Non-thermal production of quintessinoNon-thermal production of quintessino

WIMP WIMP quintessino + SM particles quintessino + SM particles ((WIMP=weakly interacting massive paricle)WIMP=weakly interacting massive paricle)

WIMPWIMP Since the interaction of quintessino is usually suppressed by Planck scale, it is generally called superWIMP.

e.g. Gravitino LSPe.g. Gravitino LSP quintessinoquintessino LKK gravitonLKK graviton

Candidates of NLSPCandidates of NLSP

neutralino/chargino NLSPneutralino/chargino NLSP slepton/sneutrino NLSPslepton/sneutrino NLSP

BBNBBN

EMEM

hadhad

BrBrhadhad O(0.01) O(0.01) Brhad O(10-3)

WIMP WIMP quintessino + SM particles quintessino + SM particles

Charged slepton, sneutrinoCharged slepton, sneutrinoOr neutralino/charginoOr neutralino/chargino

EM, had. cascade

change CMB spectrum

change light element

abundance predicted by BBN

Charged slepton NLSP are allowed by the modelCharged slepton NLSP are allowed by the model

101055 s s t t 10 1077 s s

Effects of the model

• Suppress the matter power spectrum at small scale (flat core and less galaxy satellites).

• Faraday rotation induced by quintessence.

• Suppress the abundance of 7Li.

• The lightest super partner of SM particles is stau.

Look for heavy charged particles

• A charged scalar particle with life time of 101055 s s t t 10 1077 s s and mass 100 GeV< M < TeV is predicted in the model.

• High energy comic neutrinos hit the earth and the heavy particles are produced and detected at L3C/IceCube

• Due to the R-parity conservation, always

two charged particles are produced

simultaneously and leave two parallel

tracks at the detector.

Production at colliders

• If is the LSP of SM, all SUSY particles will finally decay into and leave a track in the detector.

• Collecting these , we can study its decay process. (We can even study gravity at collider.)

• LHC/ILC can at most produce

~

~

~

~

65 1010 ～ ~Buchmuller et al 2004

Kuno et al., 2004

Feng et al., 2004

Conclusion

• In the CDM scenario, LSS form hierarchically. The MW is distributed with subhalos.

• Taking the contribution from DM annihilation into account the EGRET data can be explained perfectly. (Without DM it is difficult to explain the GeV excess even there are large uncertainties of cosmic ray propagation).

• Positron excess in HEAT can also be explained by adding contribution from DM annihilation.

• Both the EGRET data and HEAT require DM subhalos with very cuspy profile.

• A DM-DE unified model requires stau being the NLSP (gravitino model). Make different phenomenology.