Dark Matter Explanation

For e^\pm Excesses In Cosmic Ray

Xiao-Gang He

CHEP, PKU and Physics, NTU

The e^\pm Excesses In Cosmic Ray

Dark Matter Explanations Particle Physics Model Building

Discussions and Conclusions

The e^\pm Excesses in Cosmic Ray

Atic data

Astrophysics for the background

The above results agree well with more complete calculation from GalpropData from PAMELA, ATIC, FERMI and HESS show excesses compared with the above background

Origin of e+/e- excess?a. Nearby mature pulsars. In order to contribute

significantly, a pulsar cannot be either too young

nor too old.

b. Dark matter annihilation

c. Dark matter decay

No anti-proton excess. If excess is due to dark

matter, then it is leptophilic (or hadrophobic) or it

is light and is not allowed to decay or annihilate into

hadrons kinematically.

Dark Matter Explanations

Dark Matter Quest

Energy density budget of Universe from PDG, Baryon: 4.25 % Dark energy: 73(3) % Dark matter: 20 % and small portion of Others. Many weakly interacting massive particle (WIMP) models are

proposed ...

But dark matter identity and property are still not known.

♠ Introduction

DD

N N

gNNH

♦ The current and projected experimental upper limits of spin-independent WIMP-nucleon elastic cross-section as a function of WIMP mass are shown in the right figure.

♦ The effective darkon-higgs coupling is needed for elastic darkon-nucleon cross section calculation.

♠ DM Direct Search

Dark matter annihilation and Boost factor

DM contribution to e^\pm flux

An analysis based on CDM N-body simulations

shows that the boost factor from clumpy DM

distribution can hardly larger.

• Need to explain the big boost factor:

a. Non-thermal DM annihilation: decouple relic density

constraint from e^\pm excesses. Just need to fit the

Annihilation rate from the latter.

b. Sommerfeld effect. For on-relativistic scattering,

there is an enhancement factor R. Requiering light

mediating particle. For massless particle,

R = a pi/v/(1-e^{- a pi/v}) (a = coupling^2/4 pi)

c. Breit-Wigner enhancement mechanism

Annihilation rate:

v^2 depend on thermal average, if delta and gamma

small enough, annihilation rate sensitive on T, different

thermal relic density than non-resonant case, and

can produce large boost factor.

Features of PAMELA, ATIC and FERMI Data• DM mass serve as cut-off of the range of energy show e^\pm

excesses. PAMELA: positron excess in the energy range of 10 to 100

GeV. ATIC up to 650 GeV, Fermi & HESS up to 2 TeV or so.

• Excess: needs a factor of 100 to 1000 boost factor compared with

usual relic density to explain data.

• No anti-proton excess. Dynamic models: Leptophilic couplings or

Kinematic models: DM annihilate into some light particle which is not

allowed to decay into hadrons due to kinematics.

• ATIC: electron/positron excess up to 1 TeV with a sharp falling

around 650 GeV. FERMI: excess does not have sharp falling, lower

than ATIC, but extended more into higher energies.

ATIC and FERMI are in conflict, but PAMELA and ATIC or

PAMELA and FERMI can be consistently separately.

Which set is correct? An experimental issue!

• Need to explain the sharp falling at energy around 650 GeV if ATIC is correct!

If annihilation, dark matter needs to

annihilate into e+ e-

If to mu and tau pairs, secondary e- and

e+, does not have the sharp falling feature.

However, if FERMI is correct, then the other

way around!

• Needs to explain why there are excesses in electron and positron, not anti-proton from PAMELA

Dynamic model: If dark matter is the source for this,

Dark matter must be leptophilic or hadrophobic.

Or

Kinematic model: DM annihilate into some light

particles, lighter than proton + antiproton such that

baryon in the final states are suppressed.

Particle Physics Model Building

A lot of DM models not all of them can explain e^\pm excesses

• The simplest model: Darkon model: SM + a real singlet S. S – DM field. Annihilation mediated by s-channel SM Higgs. If Higgs mass is close to 2m_D, Breit-wigner mechanism can produce large boot factor, but too much anti-proton. Needs extension.

• The most popular model: LSP in MSSM. Neutralino as DM. T-channel LSP annihilation.

no mechanism for large boost factor and too much anti-proton. Needs extension. NMSSMhas all needed features. Later.

Any model can do the job? Yes, a lot of them too.

A) A leptophilic model

The PAMELA and ATIC

Case c) is out!

The PAMELA and FERMI

The FERMI data do not have sharp falling at

a certain energy, not desirable to have e+e-

directly from dark matter annihilation

Cases a) and b) are ruled out!

Will Case c) work? Yes, but with a higher

dark matter mass: 1.5 TeV

Case c) works if dark matter mass is around

1.5 TeV! But Cases a) and b) will not work

for any dark matter mass

B) A light particle decay model

Discussions and Conclusions