Celine B

1
Light Dark Matter particles
Possible detection in particle physics
experiments?
Celine Bœhm, Moriond ElectroWeak 2005
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New physics by INTEGRAL/SPI?
1. Detection of a 511 keV emission line in the
centre of the Milky Way
Explanation electron-positron annihilation
2. Possible explanations
Supernovae, Wolf-Rayet stars, Low Mass
Binaries, , Dark Matter
Celine Bœhm, Moriond ElectroWeak 2005
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Large exposure data but the Bulge is
where most of the signal comes from
Problem faced by SN, Wolf Rayet stars etc
(except LMB, DM) the ratio bulge-to-disk is
generally not large enough
Celine Bœhm, Moriond ElectroWeak 2005
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1. Results from a model fitting analysis
(modelling the source)
1e-3 ph/cm2/s
FWHM 8.5deg

2. DM must fit both the FWHM, the flux and the
ratio bulge-to-disk
Celine Bœhm, Moriond ElectroWeak 2005
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DM has a ratio bulge/disk compatible with
observations
DM annihilations into e e- can produce the
galactic positrons

• The positrons must be almost at rest
• They must lose their energy through ionization
• Once at rest, they form positronium and produce
  2 or 3 photons

This requires mDM lt 100 MeV (i.e. very light DM
particles).
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A. How light DM can be ? (Astrophysics)
Annihilations in the centre produce too much low
energy gamma rays.
(Boehm, Ensslin, Silk, 2002)
Solution The annihilation cross section must
vary with time for mdmlt 100 MeV.
Particle Physics requirement The annihilation
cross section must be dominated by a
velocity-dependent
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B. 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, Moriond ElectroWeak 2005
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Interpretation

• 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, Moriond ElectroWeak 2005
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First Results

• Flux OK with observations
• the cross section must be about five order of
  magnitude
• lower than the annihilation cross section for
  the relic density
• Z favoured!

• Halo density profile

Assumptions 1/rg as MW halo profile is still
unknown
Celine Bœhm, Moriond ElectroWeak 2005
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New Results

• taking into account more data (16 deg)

BoehmAscasibar, 2004

• Implementation of the right velocity dispersion
  profile

Celine Bœhm, Moriond ElectroWeak 2005
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New and Preliminary Results

• Implementation of the e distribution for
  realistic halo profiles
• (NFW, Moore, Binney-Evans, Isothermal) in
  INTEGRAL analysis
• (the source!)
• Implementation of the right velocity dispersion
  profile
• More data, including Dec 2004

Celine Bœhm, Moriond ElectroWeak 2005
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New results obtained in collaboration with
INTEGRAL

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Consequences

• NFW profile is THE profile that fits the data!

• Exchange of heavy particles is needed to fit the
  511 keV line

For mF 100 GeV
For mF 1 TeV
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• Fermionic DM seems to be excluded

• Decaying DM is excluded (unless ??? the profile
  is extremely cuspy)

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Consequences for Particle Physics
S. Davidson et al

• NuTeV
• Alpha value (anomalous magnetic moment of the
  electron)

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Note on Beacom et al, 2004
Mdm lt 20 MeV
because of the Final State Radiation

• But they do not compute the process.
• They use the result of e e- into mu mu-
  valid for gamma exchange which is factorizable.
• However, the F exchange is not factorizable.
• The final result could change!

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Conclusions

• NFW profile (consequences for the MW profile if
  LDM exists)

• Scalar DM

• Fermionic and decaying DM are ruled out

• Heavy fermions are required but Z exchange
  possible too

• Look like SUSY but relationship between the
  couplings and MF,
• Possible implication for NuTeV and the alpha
  value

Celine Bœhm, Moriond ElectroWeak 2005
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J. Knodlseder et al. SPI/INTEGRAL constraints
on the morphology of the galactic 511 keV line
emission