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Light DM, An interesting candidate?

Light DM, An interesting candidate?. Celine Boehm, 2004. Heavy Dark Matter TeV string candidates neutralinos GeV (proton mass) Light Dark Matter MeV `` new’’ particles? (10 -6 eV axions particles) non thermal. Weakly Interacting Massive Particles.

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Light DM, An interesting candidate?

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  1. Light DM, An interesting candidate? Celine Boehm, 2004

  2. Heavy Dark Matter TeVstring candidates neutralinos GeV(proton mass) • Light Dark Matter MeV ``new’’ particles? (10-6 eV axions particles) non thermal

  3. Weakly Interacting Massive Particles Silk (1968), Gunn et al (1978), Davis et al (1980), Peebles (1982) etc.. • No electromagnetic interactions: Weakly Interacting • Not neutrino-like: Massive Weakly Interacting Massive Particles (WIMPs) • But in fact more complicated..damping.ppt

  4. Damping constraints in a plane! One can define ``WDM’’ particles as being at the edge of the damping limit. Means also ``Collisional WDM’’!

  5. A very important criterion: Relic density at tfo

  6. The relic density criterion therefore requires: Independent of the DM mass! Too much DM The annihilation Cross section is too small One value only does the job! Not enough

  7. 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)

  8. e- dm L dm e+ Light Dark Matter (mdm < GeV) Forbidden by Lee-Weinberg because the cross section is too small! But they considered massive neutrinos and with a cross section proportional to mdm! Extension to more general DM candidates! Examples: fermions F (Dirac dm = d field)

  9. dm f+ F dm f- L How to evade Lee-Weinberg? • By just obtaining a cross section independent of mdm! • Which DM particles then? • Fermions: always proportional to mdm • Scalars: yes, some configurations OK! Almost independent of mdm ! Possible to evade Lee-Weinberg when scalars!!

  10. -2 But DM can annihilate into the galactic center… C.B., T. Ensslin, J. Silk • Gamma rays Expected between MeV and GeV depending on mdm • But already lot of observations in this range (notably OSSE!). • No indications for non standard physics so predictions have to be compatible. • Predictions depend on the DM halo profile

  11. Light DM ruled out then? • Noif the cross section ~ a + b v2 (with a << b) • Why a cross section in v2 saves the scenario? DM velocity in galaxy < 10-3 c DM velocity in primordial U ~ c • So v2 reduced the flux by a factor 10-6.. Is that possible in particle physics?

  12. Summary mid-stage Light DM OK but needs for a v2 annihilationcross section! • Fermionic DM cannot do that! • Scalar DM? • if exchange fermions: • If exchange gauge bosons?

  13. dm f+ f- dm Particle Physics models • Possible if a new gauge boson (U): U CU fU Dependence in mdm! But OK if light U and small couplings! (U of a few MeV, < GeV)

  14. Light DM finally possible because: • small couplings as required by muon and electron g-2! • Could not be seen in past colliders: • cross section smaller than at high energy because • fU is much smaller than electroweak couplings! • 2) cross section maximal at low energy (a few MeV). • Could be promising but dominated by

  15. INTEGRAL/SPI: observation of a 511 keV line emission A first evidence of Dark Matter annihilations? dm dm -> e+ e- e+ e- -> phot phot (phot) • e- and e+ at rest, • Photons with Ee, • Existence of e+ !

  16. Prospectives (dwarfs galaxies) In the sensitivity of Integral satellite If a signal is detected: confirmation of LDM If not, the LDM scenario is possibly ruled out Sagittarius Dwarf Elliptical Galaxy

  17. Heavy Dark Matter • Light DM could involves a theory that also predicts a heavy and stable particle • 2 symmetries (R and M-parities): N=2 supersymmetry?? • The relic density will be ensured by the Light DM so no restriction on the cross section

  18. Conclusion • Light Dark Matter (<GeV) is possible! • Need for v2 cross section: • possible with light scalars exchanging a light gauge boson • but other solutions may work…. • LDM explain the detection of a 511 keV line in the centre of the galaxy very well. • Possibility of having heavier stable particles…

  19. Collisionless WDM M_WDM > keV

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