Celine B

1
Is Dark Matter light?
Celine Bœhm, Unesco 2005
2
Confirmation of a 511 keV emission in the centre
of the galaxy by INTEGRAL/SPI
33deg, 16deg FoV
Narrow line which is the sign of
electron-positron annihilations at rest.
Para-positronium
Ortho-positronium
In flight annihilations
Eg me
Eg lt me
Eg lt Ee
Celine Bœhm, Unesco 2005
3
Great improvement of the sensitivity which
confirms the origin of the line and its
characteristics
Balloon experiments (HEAO3) Satellite
experiments (OSSE, INTEGRAL)
Celine Bœhm, Unesco 2005
4
Comparison between past and new measurements

• OSSE
• INTEGRAL

• Detection of 3 components
• Bulge
• Disc
• PLE
• (Positive latitude Enhancement)

• Detection of 1 component
• Bulge
• Disc but due to radioactivity
• Bulge/Discgt0.4-0.8
• No PLE

Celine Bœhm, Unesco 2005
5
Possible sources of positrons

• Stars
• SNe (Co 56)
• SNII (Al26, Ti 44)
• WR (Al 26)
• Compact sources
• Pulsars
• Black holes
• Low Mass Binaries
• Cosmic rays
• p-anti p -gt positrons
• Radioactive isotopes

General problem (except for old
populations/LMB) Too low Bulge/Disc ratio
Celine Bœhm, Unesco 2005
6
Possible source of low energy e in the GC

• LMB, old stellar population, or other unknown
  sources
• Not clear whether LMB could fit both the observed
  flux, the line width and the morphology of the
  emission, but
• Maybe new mechanisms are the answer but, in any
  case, an astrophysical explanation remains to be
  found
• New physics (or astrophysics)
• Easier in fact since the model already existed
  for other purposes!

Celine Bœhm, Unesco 2005
7
New physics at the origin of the emission(?)

• DM annihilates into electon-positron
• The positrons lose their energy through
  ionization
• Once at rest, the positrons can annihilate with
  electrons of the medium and form para-positronium
  
• The para-positronium states gives 511 keV photons
• To avoid an overproduction of low energy gamma
  rays, the DM mass must be lower than 100 MeV

e
e lose energy
(DM mass must be lt the muon threshold, to avoid
pion production)
Celine Bœhm, Unesco 2005
8
Are Light Dark Matter particles (lighter than a
proton) possible?

• Scenario proposed before INTEGRAL
• The aim was to show that it is possible to evade
  the Lee-Weinberg limit
• I.e. DM particles can be lighter than a few GeV
  but the annihilation cross section nowadays must
  be reduced compare to its value in the past
  universe by 5 order of magnitude times mdm2

Nowadays
But are their characteristics compatible with the
morphology of the 511 keV emission in the
galactic centre?
Celine Bœhm, Unesco 2005
9
First results from a model fitting analysis
(modelling the source)
10-3 ph/cm2/s
FWHM 8.5deg

Width is less than 10 keV!
Celine Bœhm, Unesco 2005
10
Naïve comparison with DM prediction!(Assuming
a DM halo profile as ?(r)?0/r)

• Full Width Half Maximum (extension)
• Flux require cross section of 10-31 cm3/s

Full width
Half maximum
Celine Bœhm, Unesco 2005
11
Needs to assume a model for the source, e.g.
gaussian, ponctual, halo/bulge model or DM
distribution
One ponctual source is excluded!
Reconstruction
J. Knodlseder et al, Lonjou et al, 2003
Celine Bœhm, Unesco 2005
12
A better Analysis was needed

• Previous results compared the FWHM expected for
  DM with that obtained assuming a gaussian
  distribution.
• That is not what one should do.
• Instead one has to determine the characteristics
  that SPI would see if DM was indeed at the origin
  of the emission
• So INTEGRAL analysis must start from the positron
  distribution as produced by DM annihilations!

Celine Bœhm, Unesco 2005
13
Elements for starting a new analysis

• Cross section depends on
• The DM mass (mdm)
• The DM energy (Edm)
• The couplings
• (The mass of the particle that is exchanged)
• DM non relativistic at annihilations.
• Thus, Edm ½ mdm v2 mdm c2
• Therefore the cross section depends on constant
  terms and v2
• A convenient decomposition is then given by
• ltsvgt a b v2 where a and b are constants.

Celine Bœhm, Unesco 2005
14
New analysis based on SPI response and background

• Testing the a-term and the b-term
• 4 different models of the DM halo

About the same as the previous version of the
model !!!
Celine Bœhm, Unesco 2005
15
Results/consequences for the model

• Decaying DM is now excluded (unless perhaps)
• An a-term is needed to fit the 511 keV emission
  but suppressed by 5 o.m
• So a b-term is needed for the relic density
• As predicted initially
• with

Contribution to b solely. Cannot explain the 511
keV line but is required for the relic density
Contribution to a AND b with ab so this diagram
MUST be suppressed But fit the 511 keV line
Celine Bœhm, Unesco 2005
16
Consequences for/Prospects in Particle Physics

• No theory but a very successful model perhaps
• But important checks to do
• Collider physics
• Neutrino physics (NuTeV)
• G-2

Celine Bœhm, Unesco 2005
17
NuTeV anomaly
S. Davidson et al, C. Boehm 2004
Celine Bœhm, Unesco 2005
18
The fine structure constant

• F particles contribution to g-2
• Deviation from SM
• Where does the anomaly come from?
• ath f(a)
• impose ath aQED and found ath
• Compare it with the experimental measurement
  Quantum Hall effect
• Using the LDM model as determined by the 511 keV
  line

(prediction also for the muon!)
For mdm6-7 MeV
19
Colliders

• Scalar
• Fermionic

Celine Bœhm, Unesco 2005
20
Conclusions

• The 511 keV line characteristics are now
  extremely well determined
• Light DM fits successfully the morphology of the
  emission while astrophysical explanations are
  still to found (but not excluded!)
• If LDM is the correct explanation, then the
  profile of the Milky Way should be cuspy (a la
  NFW)
• LDM has maybe already manifested in PP
  experiments (via g-2 experiments, --NuTeV??--).
  Needs more focus on these aspects now.
• LDM should be a scalar rather than a fermion. It
  should annihilate (not decay).
• Problem though no theory (except perhaps N2
  SUSY) but so does Lambda in fact..

Celine Bœhm, Unesco 2005
21
How light DM can be ? (Particle Physics)

• Lee-Weinberg

If DM is a fermion and coupled to heavy particles
(Z, W) then it should be heavier than a few GeV.

• Boehm-Fayet

If DM is a fermion and coupled to light particles
then it can be lighter than a few GeV.
If DM is a scalar and coupled to light or heavy
particles then it can be lighter than a few GeV.
Celine Bœhm, Unesco 2005
22

• Light scalars (BoehmFayet, 2003)

coupled to heavy particles (F)
v-independent cross section coupled to
light particles (Z) v-dependent cross
section

• Light fermions (Fayet 2004)

coupled to light particles (Z)
v-dependent cross section
Z are required to escape the Gamma ray
constraints
Celine Bœhm, Unesco 2005