Can the WIMP annihilation boost factor be boosted by the Sommerfeld enhancement?

摘要

We demonstrate that the Sommerfeld correction to CDM annihilations can beappreciable if even a small component of the dark matter is extremely cold.Subhalo substructure provides such a possibility given that the smallest clumpsare relatively cold and contain even colder substructure due to incompletephase space mixing. Leptonic channels can be enhanced for plausible models andthe solar neighbourhood boost required to account for PAMELA/ATIC data isplausibly obtained, especially in the case of a few TeV mass neutralino forwhich the Sommerfeld-corrected boost is found to be $\sim10^4-10^5.$ Saturationof the Sommerfeld effect is shown to occur below $\beta\sim 10^{-4},$ therebyconstraining the range of contributing substructures to be above $\sim 10^5\rmM_\odot.$ We find that the associated diffuse gamma ray signal fromannihilations would exceed EGRET constraints unless the channels annihilatingto heavy quarks or to gauge bosons are suppressed. The lepton channel gammarays are potentially detectable by the FERMI satellite, not from the innergalaxy where substructures are tidally disrupted, but rather as aquasi-isotropic background from the outer halo, unless the outer substructuresare much less concentrated than the inner substructures and/or the CDM densityprofile out to the virial radius steepens significantly.