Fermi/LAT observations of Dwarf Galaxies highly constrain a - PowerPoint Presentation

Slide1

Fermi/LAT observations of Dwarf Galaxies highly constrain a Dark Matter interpretation of Excess Positrons seen in AMS-02, HEAT, and PAMELA

DPF 2015 – University of Michigan, Ann Arbor.

Alejandro Lopez

in collaboration with: C. Savage, D. Spolyar and D. AdamsSlide2

Outline:

Brief Introduction

Goal

Technique

Results

Conclusion

Future WorkSlide3

Indirect Detection

χ

χ

SM

SM

Fermi/LAT

HESS

AMS

PAMELA

ICECUBE

Super-

KamiokandeSlide4

Fermi/LAT

AMS-02

M. Ackermann et al. [Fermi-LAT Collaboration

],

Phys.

Rev

. D 89

M. Boudaud et al., arXiv:1410.3799 [

astro-ph.HE]Slide5

Fermi/LAT

AMS-02

M. Ackermann et al. [Fermi-LAT Collaboration

]

,

Phys.

Rev

. D 89

M. Boudaud et al., arXiv:1410.3799 [

astro-ph.HE]Slide6

Best Fit Dark Matter models for explaining AMS-02 Positron Excess

Boudad

et al. (

arXiv:1410.3799

) three distinct dark matter annihilation channels: Single Channel: {

b¯b,e+e−,µ+µ−,τ+τ

−} MED

4 lepton case: DM + DM -> φ

+φ

-> 4 l¯l

Best Fit propagation modelMixed Channel: b¯b

+ l¯l with and without having lepton BR equal.

MED Propagation Model

Best Fit propagation model marginalized over 1623 combinations of the transport parameters {

δ,

K0, L, Vc, VA}.Slide7

Goal

To

establish if the null results from the Fermi/LAT experiment measuring gamma-rays

originating in

Dwarf

Galaxies (2014 data)

are in tension with a dark matter interpretation for the AMS-02 positron excess. Slide8

Technique

Extend Combined Likelihood Analysis done by Fermi/LAT utilizing gamma-ray data from 15 non-overlapping dwarf galaxies to dark matter masses greater than 10

TeV

in order to establish the viability for a dark matter interpretation of the AMS-02 positron excess. Slide9

Results I

Showing Fermi/LAT

bounds (blue)

and AMS-02 best

fit 2-

σ

regions. Red contour is a

ssuming MEDpropagation model, and grey region marginalizes over1623 propagation

parameters.Slide10

Results II

- Showing

Fermi/LAT bounds,

a

long with AMS-02 best fit

r

egion for single and mixed channels. Mixed channels assume MED propagation model

.- 2e and 2

μ are not excluded by Fermi/LAT, but give a bad fit

to AMS-02 data. Slide11

Results III

-Showing

Fermi/LAT bounds,

a

long with AMS-02 best fit

r

egion for 4-leptons channel.Mixed channels assume MED propagation model. Only showing 4

τ Fermi/LAT bounds, we postpone

calculation of 4µ and 4e due to

complication with Final State Radiation for future paper. 4e gives bad fit to AMS-02

Positron excess, thus potentially Only 4µ survives.

-Mixed 4-lepton channel Survives for masses > 40 TeVSlide12

Planck 2015 Results

Planck 2015 Results:

arXiv

1502.01589

We put our results on

arxiv

one month earlier Our work

: arXiv 1501.01618 Planck: arXiv

1502.01589B) Planck bounds are for much smaller range of WIMP masses

Our work: mχ=[0.350 – 30] TeV

Planck: mχ =[1 - 3] TeVSlide13

Conclusion:

For

the single channel case, we find that dark matter annihilation into

{

b¯b,e+e

−,µ+µ−,τ+τ−,4-e, or 4-τ} is ruled out as an explanation of the AMS positron excess

(

here b quarks are a proxy for all quarks, gauge and Higgs bosons

).

In addition, we find that the Fermi/LAT 2σ upper limits, assuming the best-fit AMS-02

branching ratios, exclude multichannel combinations into b¯ b and leptons.

Of all the channels we considered, the only viable channel that survives the

Fermi/LAT constraint and produces a good fit to the AMS-02 data is annihilation (via a mediator) to 4-µ,

or mainly to 4-µ in the case of multichannel combinations.

The tension between the results might relax if the branching ratios are allowed to deviate

from their best-fit values, though a substantial change would be required; the positron

excess comes partly from point sources; or there is a local dark matter

overdensity.