Beyond WIMPs: the Quark (Anti) Nugget Dark Matter

Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada

^a e-mail: arz@phas.ubc.ca

Published online: 22 March 2017

Abstract

We review a testable dark matter (DM) model outside of the standard WIMP paradigm. The model is unique in a sense that the observed ratio Ω_dark ≃ Ω_visible for visible and dark matter densities finds its natural explanation as a result of their common QCD origin when both types of matter (DM and visible) are formed during the QCD phase transition and both are proportional to single dimensional parameter of the system, Λ_qcd. We argue that the charge separation effect also inevitably occurs during the same QCD phase transition in the presence of the CP odd axion field a(x). It leads to preferential formation of one species of nuggets on the scales of the visible Universe where the axion field a(x) is coherent. A natural outcome of this preferential evolution is that only one type of the visible baryons (not anti- baryons) remain in the system after the nuggets complete their formation. Unlike conventional WIMP dark matter candidates, the nuggets and anti-nuggets are strongly interacting but macroscopically large objects. The rare events of annihilation of the anti-nuggets with visible matter lead to a number of observable effects. We argue that the relative intensities for a number of measured excesses of emission from the centre of galaxy (covering more than 11 orders of magnitude) are determined by standard and well established physics. At the same time the absolute intensity of emission is determined by a single new fundamental parameter of the theory, the axion mass, 10⁻⁶eV ≲ m_a ≲ 10⁻³eV. Finally, we comment on implications of these studies for the axion search experiments, including microwave cavity and the Orpheus experiments.