Abstract
Satellite and astrophysical data is accumulating that suggests and constrains interpretations of the dark matter of the universe. We argue there is a very well motivated theoretical framework (which existed before data) consistent with the interpretation that dark matter annihilation is being observed by the PAMELA satellite detector. The dark matter is (mainly) the neutral W boson superpartner, the wino. Using the program GALPROP extensively we study the annihilation products and the backgrounds together. A wino mass approximately in the 180–200 GeV range gives a good description of the PAMELA data, with antimatter and gammas from annihilating winos dominating the data below this energy range but not contributing above it. We explain why PAMELA data does not imply no antiproton signal was observed by PAMELA or earlier experiments, and explain why the antiproton analysis was misunderstood by earlier papers. Wino annihilation does not describe the Fermi e++e− data (except partially below ∼100 GeV). At higher energies we expect astrophysical mechanisms to contribute, and we simply parameterize them without a particular physical interpretation, and check that the combination can describe all the data. We emphasize several predictions for satellite data to test the wino interpretation, particularly the flattening or turndown of the positron and antiproton spectra above 100 GeV. It should be emphasised that most other interpretations require a large rise in the positron and antiproton rates above 100 GeV. We focus on studying this well-motivated and long predicted wino interpretation, rather than comparisons with other interpretations. We emphasize that interpretations also depend very strongly on assumptions about the cosmological history of the universe, on assumptions about the broader underlying theory context, and on propagation of antiprotons and positrons in the galaxy. The winos PAMELA is observing arose from moduli decay or other non-thermal sources rather than a universe that cooled in thermal equilibrium after the big bang. Then it is appropriate to normalize the wino density to the local relic density, and no “boost factors” are needed to obtain the reported PAMELA rates.
Highlights
How does one learn what physics interpretation to give to tentative signals of antimatter and gammas in the galaxy? Could it be due to annihilating dark matter? Answering this is not straightforward – it strongly depends on assumptions that are not always made explicit, and the answer is very sensitive to assumptions about propagation in the galaxy, and to parameters used to describe the propagation
As the recent PAMELA and Fermi satellite data appeared, essentially everyone who studied it assumed that the universe cooled in thermal equilibrium after the big bang
It has become increasingly clear that comprehensive underlying theories which explain more than one thing at a time generically have additional sources of dark matter, such as decaying particles, and that assuming thermal equilibrium as the universe cools is oversimplified and misleading
Summary
How does one learn what physics interpretation to give to tentative signals of antimatter and gammas in the galaxy? Could it be due to annihilating dark matter? Answering this is not straightforward – it strongly depends on assumptions that are not always made explicit, and the answer is very sensitive to assumptions about propagation in the galaxy, and to parameters used to describe the propagation. The winos arise continuously as the moduli decay, rather than the superpartners being mainly present at the big bang, a ”non-thermal wimp miracle” still occurs when the scaling of the Hubble parameter and cross section with temperature and mass are taken into account [4, 5, 6] This 200 GeV mass scale is just the one that is right for the PAMELA data. For entirely reasonable GALPROP parameters one can self-consistently compute the antiproton background, and with a wino annihilation signal it gives a good description of the data. We will report on studies of the GALPROP parameter degeneracies and the wino mass later, assuming our predictions for the positron and antiproton higher energy data are correct. When future data is reported we will post updated graphs at http://wino.physics.lsa.umich.edu
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