celine bœhm, moriond electroweak 2005

Celine Bœhm, Moriond ElectroWeak 2005

Light Dark Matter particles

Possible detection in particle physics experiments?


New physics by INTEGRAL/SPI?

1. Detection of a 511 keV emission line in the centre of the Milky Way

2. Possible explanations:

Explanation:electron-positron

annihilation

Supernovae, Wolf-Rayet stars, Low Mass Binaries, …, Dark Matter


r~33deg

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


1. Results from a model fitting analysis (modelling the source)

FWHM ~ 8.5deg

1e-3 ph/cm2/s

2. DM must fit both the FWHM, the flux and the ratio bulge-to-disk


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 < 100 MeV (i.e. very light DM particles).


A. How light DM can be ? (Astrophysics)

Annihilations in the centre produce too much low energy gamma rays.

Solution:

The annihilation cross section must vary with time for mdm< 100 MeV.

Particle Physics requirement:

The annihilation cross section must be dominated by a velocity-dependent

(Boehm, Ensslin, Silk, 2002)


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

Lee-Weinberg:

B. How light DM can be ? (Particle Physics)

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.


Interpretation:

Light scalars (Boehm&Fayet, 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

22 2 2 2dm

dm U Ul Ur4U

m v v C (f + f )

m


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/r

as MW halo profile is still unknown


New Results:

taking into account more data (16 deg)

Boehm&Ascasibar, 2004

Implementation of the right velocity dispersion profile


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

New results obtained in collaboration with INTEGRAL



Consequences:

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

NFW profile is THE profile that fits the data!

For mF ~100 GeV For mF ~1 TeV


Fermionic DM seems to be excluded:

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

Consequences for Particle Physics

NuTeV

Alpha value (anomalous magnetic moment of the electron)


S. Davidson et al


Note on Beacom et al, 2004

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!

Mdm < 20 MeV because of the Final State Radiation


Conclusions

Heavy fermions are required but Z’ exchange possible too

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

Scalar DM

Fermionic and decaying DM are ruled out

Look like SUSY but relationship between the couplings and MF,

Possible implication for NuTeV and the alpha value

J. Kn¨odlseder et al.: SPI/INTEGRAL constraints on the morphology of the galactic 511 keV line emission

celine bœhm, moriond electroweak 2005

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