We study a testable dark matter (DM) model outside of the standard WIMP paradigm in which 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 at the QCD phase transition and both are proportional to ΛQCD. Instead of conventional "baryogenesis" mechanism we advocate a paradigm when the "baryogenesis" is actually a charge separation process which always occur in the presence of the CP odd axion field a(x). In this scenario the global baryon number of the Universe remains zero, while the unobserved anti-baryon charge is hidden in form of heavy nuggets, similar to Witten's strangelets and compromise the DM of the Universe.In the present work we study in great details a possible formation mechanism of such macroscopically large heavy objects. We argue that the nuggets will be inevitably produced during the QCD phase transition as a result of Kibble-Zurek mechanism on formation of the topological defects during a phase transition. Relevant topological defects in our scenario are the closed bubbles made of the NDW = 1 axion domain walls. These bubbles, in general, accrete the baryon (or anti baryon) charge, which eventually result in formation of the nuggets and anti-nuggets carrying a huge baryon (anti-baryon) charge. A typical size and the baryon charge of these macroscopically large objects is mainly determined by the axion mass ma. However, the main consequence of the model, Ω dark ≈ Ω visible is insensitive to the axion mass which may assume any value within the observationally allowed window 10 −6 eV ma 10 −3 eV. We also estimate the baryon to entropy ratio η ≡ nB/nγ ∼ 10 −10 within this scenario. Finally, we comment on implications of these results to the axion search experiments, including microwave cavity and the Orpheus experiments.
We consider a dark matter (DM) model offering a very natural explanation of the observed relation, Ω dark ∼ Ω visible . This generic consequence of the model is a result of the common origin of both types of matter (DM and visible) which are formed during the same QCD transition. The masses of both types of matter in this framework are proportional to one and the same dimensional parameter of the system, ΛQCD. The focus of the present work is the detail study of the dynamics of the CP-odd coherent axion field a(x) just before the QCD transition. We argue that the baryon charge separation effect on the largest possible scales inevitably occurs as a result of merely existence of the coherent axion field in early Universe. 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 remains in the system after the nuggets complete their formation. This represents a specific mechanism on how the baryon charge separation mechanism (when the Universe is neutral, but visible part of matter consists the baryons only) replaces the conventional "baryogenesis" scenarios.
We study a dark matter (DM) model offering a very natural explanation of two (naively unrelated) problems in cosmology: the observed relation ΩDM ∼ Ω visible and the observed asymmetry between matter and antimatter in the Universe, known as the "baryogenesis" problem. In this framework, both types of matter (dark and visible) have the same QCD origin, form at the same QCD epoch, and both proportional to one and the same dimensional parameter of the system, ΛQCD, which explains how these two, naively distinct, problems could be intimately related, and could be solved simultaneously within the same framework. More specifically, the DM in this model is composed by two different ingredients: the (well-studied) DM axions and (less-studied) the quark nuggets made of matter or antimatter. The focus of the present work is the quantitative analysis of the relation between these two distinct components contributing to the dark sector of the theory determined by ΩDM ≡ [ΩDM(nuggets) + ΩDM(axion)]. We argue that the nugget's DM component always traces the visible matter density, i.e. ΩDM(nuggets) ∼ Ω visible and this feature is not sensitive to the parameters of the system such as the axion mass ma or the misalignment angle θ0. It should be contrasted with conventional axion production mechanism due to the misalignment when ΩDM(axion) is highly sensitive to the axion mass ma and the initial misalignment angle θ0. We also discuss the constraints on this model related to the inflationary scale HI , non-observation of the isocurvature perturbations and the tensor modes. We also comment on some constraints related to varies axion search experiments.
We advocate for the idea that there is a fundamentally new mechanism for axion production on Earth, as recently suggested in [1,2]. We specifically focus on production of axions within Earth, with low velocities such that they will be trapped in the gravitational field. Our computations are based on the so-called Axion Quark Nugget (AQN) dark matter model, which was originally invented to explain the similarity of the dark and visible cosmological matter densities. This occurs in the model irrespective of the axion mass ma or initial misalignment angle θ0. Annihilation of antimatter AQNs with visible matter inevitably produce axions when AQNs hit Earth. The emission rate of axions with velocities below escape velocity is very tiny compared to the overall emission, however these axions will be accumulated over the 4.5 billion year life time of the Earth, which greatly enhances the discovery potential. We perform numerical simulations with a realistically modeled incoming AQN velocity and mass distribution, and explore how AQNs interact as they travel through the interior of the Earth. We use this to estimate the axion flux on the surface of the Earth, the velocity-spectral features of trapped axions, the typical annihilation pattern of AQN, and the density profile of the axion halo around the Earth. Knowledge of these properties is necessary to make predictions for the observability of trapped axions using CAST, ADMX, MADMAX, CULTASK, ORPHEUS, ARIADNE, CASPEr, ABRACADABRA, QUAX, ORGAN, TOORAD, DM Radio.2 In particular, a first-order phase transition is not required as the axion domain wall plays the role of the squeezer. Another problem with [34,35] is that nuggets will likely evaporate on a Hubble time-scale even. For the AQN model this argument is not applicable because the vacuum-ground-state energies inside (color-superconducting phase) and outside (hadronic phase) the nugget are drastically different. Therefore, these two systems can arXiv:1905.00022v2 [astro-ph.CO]
As recently advocated in [1], there is a fundamentally new mechanism for the axion production in the Sun and Earth. However, the role of very slow axions in previous studies were neglected because of its negligible contribution to the total axion production by this new mechanism. In the present work we specifically focus on analysis of the non-relativistic axions which will be trapped by the Sun and Earth due to the gravitational forces. The corresponding emission rate of these low energy axions (below the escape velocity) is very tiny. However, these axions will be accumulated by the Sun and Earth during their life-times, i.e. 4.5 billion of years, which greatly enhances the discovery potential. The computations are based on the so-called Axion Quark Nugget (AQN) Dark Matter Model. This model was originally invented as a natural explanation of the observed ratio Ω dark ∼ Ω visible when the DM and visible matter densities assume the same order of magnitude values, irrespectively to the axion mass ma or initial misalignment angle θ0. This model, without adjustment of any parameters, gives a very reasonable intensity of the extreme UV (EUV) radiation from the solar corona as a result of the AQN annihilation events with the solar material. This extra energy released in corona represents a resolution, within AQN framework, a long standing puzzle known in the literature as the "solar corona heating mystery". The same annihilation events also produce the axions. The flux of these axions is unambiguously fixed in this model and expressed in terms of the EUV luminosity from solar corona. We make few comments on the potential discovery of these gravitationally bound axions. * xunyul@phas.ubc.ca † arz@physics.ubc.ca arXiv:1810.00673v2 [hep-ph] 8 Jan 20191 According to the most recent computations presented in ref. [20], the axion contribution to Ω DM as a result of decay of the topological objects can saturate the observed DM density today if the axion mass is in the range ma = (2.62 ± 0.34)10 −5 eV, while the earlier estimates suggest that the saturation occurs at a larger axion mass. One should also emphasize that the computations [15][16][17][18][19][20] have been performed with assumption that PQ symmetry was broken after inflation.
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