DPF 2015 University of Michigan Ann Arbor Alejandro Lopez in collaboration with C Savage D Spolyar and D Adams Outline Brief Introduction Goal Technique Results Conclusion Future Work ID: 920479
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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. Adams
Slide2Outline:
Brief Introduction
Goal
Technique
Results
Conclusion
Future Work
Slide3Indirect Detection
χ
χ
SM
SM
Fermi/LAT
HESS
AMS
PAMELA
ICECUBE
Super-
Kamiokande
Slide4Fermi/LAT
AMS-02
M. Ackermann et al. [Fermi-LAT Collaboration
],
Phys.
Rev
. D 89
M. Boudaud et al., arXiv:1410.3799 [
astro-ph.HE]
Slide5Fermi/LAT
AMS-02
M. Ackermann et al. [Fermi-LAT Collaboration
]
,
Phys.
Rev
. D 89
M. Boudaud et al., arXiv:1410.3799 [
astro-ph.HE]
Slide6Best 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}.
Slide7Goal
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.
Slide8Technique
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.
Slide9Results 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.
Slide10Results 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.
Slide11Results 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 TeV
Slide12Planck 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] TeV
Slide13Conclusion:
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.