Origins of Hidden Sector Dark Matter I: Cosmology

We present a systematic cosmological study of a universe in which the visible sector is coupled, albeit very weakly, to a hidden sector comprised of its own set of particles and interactions. Assuming that dark matter (DM) resides in the hidden sector and is charged under a stabilizing symmetry shared by both sectors, we determine all possible origins of weak-scale DM allowed within this broad framework. We show that DM can arise only through a handful of mechanisms, lending particular focus to Freeze-Out and Decay and Freeze-In, as well as their variations involving late time re-annihilations of DM and DM particle anti-particle asymmetries. Much like standard Freeze-Out, where the abundance of DM depends only on the annihilation cross-section of the DM particle, these mechanisms depend only on a very small subset of physical parameters, many of which may be measured directly at the LHC. In particular, we show that each DM production mechanism is associated with a distinctive window in lifetimes and cross-sections for particles which may be produced in the near future. We evaluate prospects for employing the LHC to definitively reconstruct the origin of DM in a companion paper.Comment: 32 pages, 19 figures; v2: references added, published versio

Contact based void partitioning to assess filtration properties in DEM simulations

Discrete element method (DEM) simulations model the behaviour of a granular material by explicitly considering the individual particles. In principle, DEM analyses then provide a means to relate particle scale mechanisms with the overall, macro-scale response. However, interpretative algorithms must be applied to gain useful scientific insight using the very large amount of data available from DEM simulations. The particle and contact coordinates as well as the contact orientations can be directly obtained from a DEM simulation and the application of measures such as the coordination number and the fabric tensor to describe these data is now well-established. However, a granular material has two phases and a full description of the material also requires consideration of the voids. Quantitative analysis of the void space can give further insight into directional fabric and is also useful in assessing the filtration characteristics of a granular material. The void topology is not directly given by the DEM simulation data; rather it must be inferred from the geometry of particle phase. The current study considers the use of the contact coordinates to partition the void space for 3D DEM simulation datasets and to define individual voids as well as the boundaries or constrictions between the voids. The measured constriction sizes are comparable to those calculated using Delaunay-triangulation based methods, and the contact-based method has the advantage of being less subjective. In an example application, the method was applied to DEM models of reservoir sandstones to establish the relationship between particle and constriction sizes as well as the relationship between the void topology and the coordination number and the evolution of these properties during shearing

Proximal Fifth Metatarsal Fractures: Anatomy, Classification, Treatment and Complications

Context: Fractures of proximal fifth metatarsal are one of the most common fractures of the foot. Evidence Acquisition: A search of PubMed for studies on proximal fifth metatarsal fracture and Jones fracture focusing on the classification and management was performed. The reference list of the retrieved articles was searched for additional related studies. Results: The vascular supply and soft tissue anatomy of the fifth metatarsal explains the increased risk of delayed union and non-union in fractures at the metaphyseal-diaphyseal junction. Lawrence and Botte classify proximal fifth metatarsal fractures according to their location: tuberosity avulsion fractures (zone 1), fractures at metaphyseal-diaphyseal junction extending into the fourth-fifth intermetatarsal joint (zone 2) and proximal diaphyseal fractures (zone 3). Zone 1 fractures are treated conservatively with functional immobilization and early mobilization with excellent outcome. For zone 2 and zone 3 fractures, acute forms can be treated conservatively but with a risk of delayed union time and time for return to function. Therefore, early surgical fixation with intramedullary screw is advised in athletic individuals. For cases presented with signs of delayed union and non-union, surgical treatment with or without bone grafting is recommended. Complications of these fractures and their management are discussed in this report. Conclusions: Lawrence and Botte’s classification of proximal fifth metatarsal fractures is recommended by experts, due to its implication on prognosis and treatment strategy. Zone 1 fractures should be treated conservatively due to their excellent healing potential. Early operative treatment is advised for zone 2 and zone 3 fractures, especially in the athletic group. Complications of delayed union, non-union and refractures should be treated by revision fixation and bone grafting