Black hole merger simulations in wave dark matter environments

The interaction of binary black hole mergers with their environments can be studied using numerical relativity simulations. These start only a short finite time before merger, at which point appropriate initial conditions must be imposed. A key task is therefore to identify the configuration that is appropriate for the binary and its environment at this stage of the evolution. In this work we study the behavior of wave dark matter around equal mass black hole binaries, finding that there is a preferred, quasistationary profile that persists and grows over multiple orbits, in contrast to heavier mass dark matter where any overdensity tends to be dispersed by the binary motion. While different initial configurations converge to the preferred quasistationary one after several orbits, unwanted transient oscillations are generated in the process, which may have an impact on the signal in short simulation runs. We also point out that naively superimposing the matter onto a circular binary results in artificially eccentric orbits due to the matter backreaction, which is an effect of the initial conditions and not a signature of dark matter. We discuss the further work required so that comparison of waveforms obtained with environments to vacuum cases can be done in a meaningful way

The effects of potential shape on inhomogeneous inflation

We study the robustness of single-field inflation against inhomogeneities. We derive a simple analytic criterion on the shape of the potential for successful inflation in the presence of inhomogeneities, and demonstrate its validity using full 3+1 dimensional numerical relativity simulations on several classes of popular models of single-field inflation. We find that models with convex potentials are more robust to inhomogeneities than those with concave potentials, and that concave potentials that vary on super-Planckian scales are significantly more robust than those that vary on sub-Planckian scales.Comment: 16 pages, 12 figures. Summary video: https://youtu.be/yk9sGuG8hd

Effect of Wave Dark Matter on Equal Mass Black Hole Mergers.

For dark matter to be detectable with gravitational waves from binary black holes, it must reach higher than average densities in their vicinity. In the case of light (wavelike) dark matter, the density of dark matter between the binary can be significantly enhanced by accretion from the surrounding environment. Here we show that the resulting dephasing effect on the last ten orbits of an equal mass binary is maximized when the Compton wavelength of the scalar particle is comparable to the orbital separation, 2π/μ∼d. The phenomenology of the effect is different from the channels that are usually discussed, where dynamical friction (along the orbital path) and radiation of energy and angular momentum drive the dephasing, and is rather dominated by the radial force (the spacetime curvature in the radial direction) towards the overdensity between the black holes. While our numerical studies limit us to scales of the same order, this effect may persist at larger separations and/or particle masses, playing a significant role in the merger history of binaries

Lessons for adaptive mesh refinement in numerical relativity

Funder: Queen’s College, University of Oxford; doi: https://doi.org/10.13039/100010356Funder: Homerton College, University of Cambridge; doi: https://doi.org/10.13039/501100008420We demonstrate the flexibility and utility of the Berger-Rigoutsos Adaptive Mesh Refinement (AMR) algorithm used in the open-source numerical relativity code GRChombo for generating gravitational waveforms from binary black-hole inspirals, and for studying other problems involving non-trivial matter configurations. We show that GRChombo can produce high quality binary black-hole waveforms through a code comparison with the established numerical relativity code Lean. We also discuss some of the technical challenges involved in making use of full AMR (as opposed to, e.g. moving box mesh refinement), including the numerical effects caused by using various refinement criteria when regridding. We suggest several "rules of thumb" for when to use different tagging criteria for simulating a variety of physical phenomena. We demonstrate the use of these different criteria through example evolutions of a scalar field theory. Finally, we also review the current status and general capabilities of GRChombo

Impact performance prediction of injection-molded talc-filled polypropylene through thermomechanical environment assessment

Due to the fact that different injection molding conditions tailor the mechanical response of the thermoplastic material, such effect must be considered earlier in the product development process. The existing approaches implemented in different commercial software solutions are very limited in their capabilities to estimate the influence of processing conditions on the mechanical properties. Thus, the accuracy of predictive simulations could be improved. In this study, we demonstrate how to establish straightforward processing-impact property relationships of talc-filled injection-molded polypropylene disc-shaped parts by assessing the thermomechanical environment (TME). To investigate the relationship between impact properties and the key operative variables (flow rate, melt and mold temperature, and holding pressure), the design of experiments approach was applied to systematically vary the TME of molded samples. The TME is characterized on computer flow simulation outputsanddefined bytwo thermomechanical indices (TMI): the cooling index (CI; associated to the core features) and the thermo-stress index (TSI; related to the skin features). The TMI methodology coupled to an integrated simulation program has been developed as a tool to predict the impact response. The dynamic impact properties (peak force, peak energy, and puncture energy) were evaluated using instrumented falling weight impact tests and were all found to be similarly affected by the imposed TME. The most important molding parameters affecting the impact properties were found to be the processing temperatures (melt andmold). CI revealed greater importance for the impact response than TSI. The developed integrative tool provided truthful predictions for the envisaged impact properties.Foundation for Science and Technology, Lisbon, through the 3° Quadro Comunitário de Apoio, and the POCTI and FEDER programs, and project PEst-C/CTM/LA0025/2013

Thermomechanical environment characterisation in injection moulding and its relation to the mechanical properties of talc-filled polypropylene

This study is focused on the establishment of relationships between the injection moulding processing conditions, the applied thermomechanical environment (TME) and the tensile properties of talc-filled polypropylene, adopting a new extended concept of thermomechanical indices (TMI). In this approach, TMI are calculated from computational simulations of the moulding process that characterise the TME during processing, which are then related to the mechanical properties of the mouldings. In this study, this concept is extended to both the filling and the packing phases, with new TMI defined related to the morphology developed during these phases. A design of experiments approach based on Taguchi orthogonal arrays was adopted to vary the injection moulding parameters (injection flow rate, injection temperature, mould wall temperature and holding pressure), and thus, the TME. Results from analysis of variance for injection-moulded tensile specimens have shown that among the considered processing conditions, the flow rate is the most significant parameter for the Young’s modulus; the flow rate and melt temperature are the most significant for the strain at break; and the holding pressure and flow rate are the most significant for the stress at yield. The yield stress and Young’s modulus were found to be governed mostly by the thermostress index (TSI, related to the orientation of the skin layer), whilst the strain at break depends on both the TSI and the cooling index (CI, associated to the crystallinity degree of the core region). The proposed TMI approach provides predictive capabilities of the mechanical response of injection-moulded components, which is a valuable input during their design stage.Foundation for Science and Technology, Lisbon, through the 3 Quadro Comunita´rio de Apoio, the POCTI and FEDER programs, and project PEst-C/CTM/LA0025/2011