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

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

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

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

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

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

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

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

Celine Bœhm, Geneva 2005 r~33deg 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 Where the line come from!

Possible sources de positrons (P. Jean, + Low Mass Binaries Celine Bœhm, Geneva 2005

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

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

Celine Bœhm, Geneva 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

Celine Bœhm, Geneva 2005 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 m DM < 100 MeV (i.e. very light DM particles). 2 E(e) = 2 mdm

Celine Bœhm, Geneva 2005 A. How light DM can be ? (Astrophysics) 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 (Boehm, Ensslin, Silk, 2002)

Celine Bœhm, Geneva 2005 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.

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

The phenomenology of the model Scalar DM: Fermionic DM:

Celine Bœhm, Geneva 2005 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

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 Annihilation cross sections for fermions Celine Bœhm, Geneva 2005

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/r  as MW halo profile is still unknown

Celine Bœhm, Geneva 2005 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 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

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

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

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

A. Consequences for Particle Physics  Z’ changes the neutrino-electron elastic scattering cross section. [σ(νμ N -> νμ X) - σ(νμ N -> νμ X)] = (g l 2 –g r 2 ) [σ(νμ N -> μ X) - σ(νμ N -> μ X)] With g l,r 2 = [(g l,r u ) 2 + (g l,r d ) 2 ]/4 and g l,r f = 2 (T3(f l,r ) - Q(f) Sin ΘW on shell 2 ) ν e e ν Celine Bœhm, Geneva 2005 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

Consequences for Particle Physics Celine Bœhm, Geneva 2005 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 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. B- Consequences of (heavy fermionic) F particles

Celine Bœhm, Geneva 2005 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 and also at high energy.  However, the F exchange is not factorizable.  The final result could change! Mdm < 20 MeVbecause of the Final State Radiation

Celine Bœhm, Geneva 2005 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

The coded mask together with the detector plane define an angular resolution of about 2.5° within a fully coded field of view of 16° x 16°. The partially coded field of view is 34° x 34° while the anticoincidence shield defining a hexagonal aperture of ~ 25° FWHM. The point source location is better than 2° and improves with source intensity and exposure time. The example shown here demonstrates SPI’s imaging capabilities by folding the Galactic 511 keV skymap through a detailed model of the spectrometer. The resulting skymap was obtained by simulating a galactic plane survey of SPI with a realistic background which slightly varied with time. The calculations of SPI’s imaging performance have been performed at the University of Birmingham, UK.