Milky Way Dark Halo Profile with Light Dark Matter

1. What would be the shape of the Milky Way Dark halo profile if DM was light? Celine Bœhm, Geneva 2005

2. New physics at the centre of our galaxy? 1. Detection of a 511 keV emission line in the centre of the Milky Way INTEGRAL/SPI 2. Interpretation:electron-positron annihilation (positronium formation) Celine Bœhm, Geneva 2005

3. e+ e- Interpretation: 1.Para-positronium 511 keV line signal! • Confirmation of a low energy positrons in the centre of the galaxy ~ 95% of the events detected 2 photon production from e+e- at rest. Kinematics: 2 me = 2 E(photon) 2. Ortho-positronium 2 photon production from e+e- at rest. Kinematics: 2 me = 3 E(photon) 3. In flight 2 photon production from energetic e+e-. Kinematics: 2 E(e)= 2 E(photon) Celine Bœhm, Geneva 2005

4. Quick reminder on positronium formation Possible states: Ortho-positronium S=1 so 3 photons Para-positronium S=1 so 2 photons Celine Bœhm, Geneva 2005

5. Past and present observations of the 511 keV line INTEGRAL is not the first but its sensitivity is very good and it can map the emission. Celine Bœhm, Geneva 2005

6. Just a simple comparison: • Detection of 3 components: • Bulge • Disc • PLE • (Positive latitude Enhancement) • OSSE: • INTEGRAL: • Detection of 1 component: • The bulge! • Disc absent but B/D>0.4-0.8 • No PLE • (Positive latitude Enhancement) Celine Bœhm, Geneva 2005

7. INTErnational Gamma RayLaboratory Cryostat Germanium Dectector Coded mask Anticoincidence shield Fully coded FoV: 16deg*16 The aperture system provides the imaging capabilities of instrument Celine Bœhm, Geneva 2005

8. Reconstruction Needs to assume a model for the source, e.g. gaussian, ponctual. J. Knodlseder et al, Lonjou et al, … Celine Bœhm, Geneva 2005

9. r~33deg Where the line come from! INTEGRAL has large exposure data but most of the signal comes from only 9 deg, i.e. the inner part of the galaxy. After reconstruction, they can exclude an unique source (if ponctual) but several could explain the emission. If the source is gaussian, then it is possible to deduce the Full Width Half Maximum Celine Bœhm, Geneva 2005

10. Possible sources de positrons (P. Jean, http://www.cesr.fr/~marcowit/PierreJean.pdf) + Low Mass Binaries Celine Bœhm, Geneva 2005

11. But a problem faced by SN, Wolf Rayet stars etc (except LMB, DM): the ratio bulge-to-disk is generally not large enough (some sources being mostly in the disc) Need for an old stellar population or exotic source The explanation is therefore likely to be a sign of new physics, whether it is astrophysical or from particle physics. But one needs to be careful as long as the origin of galactic positrons is a not properly identified. Celine Bœhm, Geneva 2005

12. Can Dark Matter fit the characteristics of the signal detected and mapped by INTEGRAL/SPI?

13. 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, Geneva 2005

14. 2 E(e) = 2 mdm 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). Celine Bœhm, Geneva 2005

15. A. How light DM can be ? (Astrophysics) (Boehm, Ensslin, Silk, 2002) Annihilations of Light DM (<100 MeV) in the centre of the MW will produce too much low energy gamma rays compare to observations. Caveat: True only if one considers an annihilation cross section that allows to get the correct relic density. 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 Celine Bœhm, Geneva 2005

16. B. 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, Geneva 2005

17. dm f f dm First calculations to be done: Lee-Weinberg (1977) Massive neutrinos, Fermi interactions: • Depends mainly on mdm, • if mdm too small, Wdm> 1 ! Lee-Weinberg limit: mdm < O(GeV)

18. The phenomenology of the model • Scalar DM: • Fermionic DM:

19. Annihilation cross sections for scalars • scalars coupled to heavy particles (F): v-independent cross section • scalars coupled to light particles (Z’): v-dependent cross section Celine Bœhm, Geneva 2005

20. Annihilation cross sections for fermions • Fermions coupled to heavy particles (F): v-independent cross section Depends on whether Majorana or Dirac. Here Majorana (Boehm&Fayet 2003) • fermions coupled to Z’: v-dependent cross section MeV fermions/scalars: Z’ are required to escape the Gamma ray constraints Celine Bœhm, Geneva 2005

21. First results (CB, D. Hooper, J. Silk et al) • 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, Geneva 2005

22. Improved Results (CB, Y. Ascasibar, 2004) • taking into account more data (16 deg) Boehm&Ascasibar, 2004 • Implementation of the right velocity dispersion profile Celine Bœhm, Geneva 2005

23. New (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, Geneva 2005

24. New results obtained in collaboration with INTEGRAL Celine Bœhm, Geneva 2005

25. 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 Celine Bœhm, Geneva 2005

26. Fermionic DM seems to be excluded: • Decaying DM is excluded (unless ??? the profile is extremely cuspy): Celine Bœhm, Geneva 2005

27. ν ν e e A. Consequences for Particle Physics • Z’ changes the neutrino-electron elastic scattering cross section. [σ(νμ N -> νμ X) - σ(νμ N -> νμ X)] --------------------------------------------- = (gl2 –gr2) [σ(νμ N -> μ X) - σ(νμ N -> μ X)] With gl,r2 = [(gl,ru) 2 + (gl,rd)2]/4 and gl,rf = 2 (T3(fl,r) - Q(f) Sin ΘW on shell2) • QED/EW corrections • QCD corrections: perturbative QCD charged current charm production Parton distributions Isospin breaking Nuclear effects Experimental effects • Possible solution: Asymmetric strange sea Isospin violation in parton distribution Celine Bœhm, Geneva 2005

28. Consequences for Particle Physics S. Davidson et al mentioned that a light Z’ could explain the NuTeV anomaly CB 2004, yes it is true and in agreement with the LDM but tests to make first. Celine Bœhm, Geneva 2005

29. B- Consequences of (heavy fermionic) F particles • The measured value of alpha is not in agreement with the value obtained from the g-2 of electrons. • Generally the discrepancy is disregarded because there is no simple explanation but with LDM (F particles) one change the expression of the g-2 of electrons and one obtains a perfect agreement for mdm < 20 MeV. Celine Bœhm, Geneva 2005

30. Note on Beacom et al, 2004 Mdm < 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 and also at high energy. • However, the F exchange is not factorizable. • The final result could change! Celine Bœhm, Geneva 2005

31. 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, Geneva 2005