Leptophilic Dark Matter from ATIC and Pamela

Xiao-Gang He

National Taiwan University

In Collaboration with Xiao-Jun BiarXiv: 0903.0122

Evidences for Dark Matter

The ATIC and PAMELA Data

A Model for Leptophilic Dark Matter Discussions and Conclusions

Evidences for Dark Matter

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

Big-Bang Nucleosynthesis

WMAP Results on CMB (2003)

Rotation velocity v->Sqrt[1/r] away from optical disc if there is nothing between. But observation show differently.

Gravitational lensing

Non-Interacting Dark Matter?

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

ATIC and PAMELA Data

Atic data

Features of ATIC and PAMELA Data

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

Excess: needs a factor of 100 to 1000 boost factor

compared with usual relic density to explain data.• 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.

• ATIC: electron/positron excess up to 1 TeV with a sharp falling around 650 GeV.

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 kinematicaly.

• Need to explain the big boost factor:

a. An analysis based on CDM N-body simulations

shows that the boost factor from clumpy DM distribution

can hardly larger.

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. Non-thermal relic dark matter

d. Dark matter decay

e. 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.

• Need to explain the sharp falling at energy around 650 GeV

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.

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

If dark matter is the source for this, Dark

matter must be leptophilic or hadrophobic.

A Model for Leptophilic Dark Matter

Discussions and Conclusions