Infering Annihilation Channels of Neutralinos in Galactic Halos

Abstract

Applying the microcanonical definition of entropy to a weakly interacting and self–gravitating neutralino gas, we evaluate the change in the local entropy per particle of this gas between the freeze out era and present day virialized halo structures. An “entropy consistency” criterion emerges by comparing the obtained theoretical entropy per particle of the virialized halos with an empirical entropy per particle given in terms of dynamical halo variables of actual galactic structures. We apply this criterion to the cases when neutralinos are mostly B-inos and mostly Higgsinos, in conjunction with the usual “abundance” criterion requiring that present neutralino relic density complies with $0.2<\Omega_{{\tilde\chi^1_0}} < 0.4$ for h≃ 0.65. The joint application of both criteria reveals that a much better fitting occurs for the B-ino than for the Higgsino channels, so that the former seems to be a favored channel along the mass range of $150\,\hbox{GeV} < m_{{\tilde\chi^1_0}} < 250 \,\hbox{GeV}$. These results are consistent with neutralino annihilation patterns that emerge from recent theoretical analysis on cosmic ray positron excess data reported by the HEAT collaboration. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates of thermal WIMP gas relics.