Implications of the AMS-02 results on dark matter annihilation and decay

Yu-Feng Zhou

arXiv:1304.1997Collaborators: Hong-Bo Jin and Yue-Liang Wu

State Key Lab for Theoretical Physics, Kavli Institute for Theoretical Physics China,

Institute of Theoretical Physics, Chinese Academy of Sciences 1

Outline

• A brief introduction to DM • The AMS-02 results • DM interpretations

• DM annihilation• DM decay

• Symmetric DM decay• Asymmetric DM decay

• Conclusions

2

DM revealed from gravitational effects

Gravitational curves

Strong lensing

Weak lensing

Large scale structure

CMB

Bullet clusters

Planck13: DE:68%, DM:27%, Atom:5%arXiv:1303.5062

Weakly interacting massive particles (WIMPs)

Weakly Interacting Massive Particles (WIMPs)• Particle physics independently predicts WIMPs• WIMPs have just the right thermal relic density• WIMPs are testable by the current exp.

Searching for WIMPs

space

underground

ground

atmosphere

laboratory

Cosmic-rays: positron fraction

PAMELA, Nature 458, 607 (2009) FERMI

Cosmic-rays: electrons + positrons

ATIC, Nature, 456, 2008,362-365 Fermi-LAT, Phys.Rev.Lett.102:181101,2009

Fermi did not confirm PAMELA excess

Cosmic-rays: electron + positronHESS • No feature below TeV• Spectrum drop off above TeV

Astron.AstronPhys.508,561,2009 [arXiv0905.0105]

Cosmic-ray antiprotons

PAMELA, 0810.4994, 1103.4055,BESS POLAR II, 1107.6000

BESS Polar II extended pbar flux to 0.2 GeVNo excess observed

No excess in antiproton/proton

Antiproton data rule out IVDMH.B.Jin, S.Miao, YFZ, 1207.4408, PRD

AMS-02: e+/(e++e-)

10

PRL, 110, 141102 (2013)

• Positron fraction measured from 0.5 to 350 GeV• In total 6.8x106 positron and electron events presented• Positron spectrum is steadily increasing from 10 to ~250 GeV• The slope decreases by an order of magnitude from 20 to ~250 GeV

11Limits on the amplitude of a dipole anisotropy <0.03 at 95% C.L

12

Positron spectrum up to 350 GeV

13

Electron spectrum from 1 GeV – 500 GeV

14

All electron from 0.5 GeV – 700 GeV

15

AMS-02 did not confirm the substructures observed by PAMELA

Implications

• A rising spectrum of positron fraction, confirming the existence of extra primary positron sources.

• The excess is isotropic, consistent with DM origin, but so far cannot rule out contributions from nearby pulsars.

• • The slope of the spectrum decreases by an order or

magnitude from ~20-250 GeV, disfavor heavy DM around TeV scale

• Unprecedented precision due to high statistics, useful in distinguishing DM models. 16

DM interpretation ?

17

How electrons/positrons travel in the Galaxy

Maurin, etal, astro-ph/0212111

18

Cosmic-ray antiprotons

Diffusion

diffusion convection

reaccelaration

E-loss

source

Reaccelaration

Convection

19

Secondary source (Spalation)

Primary source (SNR)

Electron/positron loss energy due to the magnetic fields, inverse Compton scattering etc..

Sources from DM annihilation/decay

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DM annihilation, proportional to ρ(x)2

DM halo profile (Einasto)

DM decay, proportional ρ(x), charge symmetric/asymmetric

propagation models

Benchmark models• The conventional model (Model A) Strong, Moskalenko, astro-ph/0101068, • The constrained Model (Model B ) from global Byesian fit to

B/C, 10Be/9 Be, Carbon, Oxegen, etc. Trotta, etal, arXiv:1011.0037

21

Uncertainties and correlations of propagation parameters

Uncertainties in parameters

22

Modifications of Model B with variations in • C1(C2):Diffusion halo height Zh and diffusion coefficient D0

• D1(D2)Power index δ2

• E1(E2) Power index primary proton γp2

Uncertainties in parameters

23

Instead of varying the power index primary electron γe2,

the normalization and slope of primary electron flux are set free.

At high energies

The cross section and k are nearly degenerate in positron fraction

Data selection

• Data included ( energy >20 GeV, to avoid solar modulation)• PAMELA positron fraction ( 4 data points) • Fermi-LAT positron fraction (10 data points)• AMS02 positron fraction (31 data points)• Fermi-LAT electron+positron (28 data points)• PAMELA electron (18 data points)• AMS02 electron (35 data points)

• Energy resolution of each exp. taken into account• PAMELA: 5%• Fermi-LAT: 6% at 7GeV, 15% at 1TeV• AMS02: 1.4% at 100 GeV and above

24

Results for DM annihilation

25

Quality of Fits: 2e,4e highly inconsistent, 2μ, 4μ not good, 2τ, 4τ good

χχ e+e-, spectra too sharp

262e and 4e channels are inconsistent with AMS02 and Fermi-LAT

Results: χχ μ+μ-

27

at 99%C.L.

at 99.99999%C.L.

Fermi

AMS02

Fermi

AMS02

AMS02 inconsistent with Fermi-LAT for 2μ channel

Results: χχ μ+μ-μ+μ-

28

at 99%C.L.

at 99.99999%C.L.

Fermi

AMS02

Fermi

AMS02

AMS02 inconsistent with Fermi-LAT For 4μ channel

Variation of Zh and D0

29Tension between AMS02 and Fermi-LAT Slightly reduce with large Zh=, D0=

Variation of δ2 and γp2

30

The tension between AMS02 and Fermi-LAT remains

Results: χχ τ+τ-

31

at 99%C.L.

at 99.99999%C.L.

Fermi

AMS02

Fermi

AMS02

DM decay:χχ τ+τ-τ+τ-

32

at 99%C.L.

at 99.99999%C.L.

Fermi

AMS02

Fermi

AMS02

Results for DM decay

33

Quality of Fits: DM decay not as good as DM annihilation

Allowed regions

34

Fermi

AMS02 Fermi

AMS02

DM asymmetric decay

35

Source term

For fixed background κ=0.85, δ=0 For varying backgrounds

Conclusions

• The precision AMS-02 data provide us rich information. Different DM models can de distinguished

• DM annihilation into 2μ, 4μ which were favored by the PAMELA and Fermi-LAT, is not favored by the AMS-02 data. The conclusion is robust against the variation of propagation modes and the normalization of electron backgrounds.

• More consistent fits obtained for 2τ, 4τ channels• AMS-02 data favor DM annihilation over DM decay.• Asymmetric DM decay can slightly favored over the symmetric

case.

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