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Celine Bœhm, Unesco 2005

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Celine Bœhm, Unesco 2005

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  1. Status and prospects of the Light Dark Matter scenario in view of the 511 keV line Is Dark Matter light? Celine Bœhm, Unesco 2005

  2. Confirmation of a 511 keV emission in the centre of the galaxy by INTEGRAL/SPI e+ e+ e-g g e- 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 < me Eg < 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 : • Detection of 3 components: • Bulge • Disc • PLE • (Positive latitude Enhancement) • OSSE: • INTEGRAL: • Detection of 1 component: • Bulge • Disc but due to radioactivity • Bulge/Disc>0.4-0.8 • 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 -> 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, orother 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. dm e- e+ e+ dm e- 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 < 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 ρ(r)≈ρ0/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 mdmv2 + mdm c2 • Therefore the cross section depends on constant terms and v2 • A convenient decomposition is then given by: <σv> = a + bv2 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 a AND b with a=b so this diagram MUST be suppressed But fit the 511 keV line Contribution to b solely. Cannot explain the 511 keV line but is required for the relic density 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(α) • impose ath = aQED and found αth • 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 mdm~6-7 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 N=2 SUSY) but so does Lambda in fact.. Celine Bœhm, Unesco 2005

  21. How light DM can be ? (Particle Physics) • Lee-Weinberg: If DM is afermionand coupled toheavyparticles (Z, W) then it should beheavier than a few GeV. • Boehm-Fayet: If DM is afermionand coupled tolightparticles then it can belighter than a few GeV. If DM is ascalarand coupled tolightorheavyparticles then it can belighter than a few GeV. Celine Bœhm, Unesco 2005

  22. 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 Celine Bœhm, Unesco 2005