Thursday, October 15, 2009

FERMI does not confirm the rise in positron fraction with energy...:(

Today I saw a paper by W. de Boer titled "Indirect Dark Matter Searches in the Light of ATIC, FERMI, EGRET and PAMELA" (http://arxiv.org/abs/0910.2601). It is related to the Invited talk at SUSY09, the 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions, Boston, 2009. The author gives a good comparison between the results from various experiments related to cosmic ray positron excess. I must say after looking at the FERMI results in this paper I am not that much enthusiastic about working on the dark matter interpretation of positron excess as I was when I first saw PAMELA results. The basic difference between latest FERMI data is that it does not confirm the peak in positron fraction at several hundreds GeV. The FERMI spectrum is more or less flat. The plot shown in the paper is as follows
The author has mentioned all the attempts so far for the positron excess explanation and commented that all the explanations seem correct and nobody can rule out any one of them. He has considered contribution of all such effects in the paper. I was particularly interested in dark matter interpretation of this excess which was quite interesting as well as challenging, since you need to make your particle physics model such that the proposed dark matter candidate unlike neutralinos annihilate primarily into leptons and not hadrons. Anyway as the author says we should wait for the future FERMI data which might focus more on possible dark matter link.

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