The CMB in a Causal Set Universe

We discuss Cosmic Microwave Background constraints on the causal set theory of quantum gravity, which has made testable predictions about the nature of dark energy. We flesh out previously discussed heuristic constraints by showing how the power spectrum of causal set dark energy fluctuations can be found from the overlap volumes of past light cones of points in the universe. Using a modified Boltzmann code we put constraints on the single parameter of the theory that are somewhat stronger than previous ones. We conclude that causal set theory cannot explain late-time acceleration without radical alterations to General Relativity.Comment: 5 pages, 2 figure

Refugees’ transnational livelihoods and remittances:Syrian mobilities in the Middle East before and after 2011

Pursuing an ethnographic approach, this article explores how Syrians’ pre-war kinship-based networks have oriented livelihoods strategies for refugees in Jordan after 2011. Drawing on long-term fieldwork (2015–2017) in northern Jordan, I argue that seasonal migration was a livelihoods strategy for Syria’s rural poor long before 2011, serving as their old-age provision and contributing to rural development. Since 2011, conflict-induced displacement and border closures have reshaped Syrians’ transnational kinship-based networks: geographically, but also with regard to the diversification of sources of income and gendered responsibilities. In Jordan, Syrian refugees mobilize pre-war transnational ties to access jobs in agriculture and the humanitarian sector, and distribute their income through kinship-based cross-border networks. These ethnographic findings challenge a localized understanding of refugee livelihoods, demonstrating that the household economies of refugees, migrants, and those left behind, in Syria, Jordan, the Gulf countries, and now Europe, are intertwined. In closing, I provide recommendations about how a networked understanding of refugee livelihoods can inform the COVID-19 emergency response, and help create decent jobs for displaced people in the Global South

Cosmic Discordance: Are Planck CMB and CFHTLenS weak lensing measurements out of tune?

We examine the level of agreement between low redshift weak lensing data and the CMB using measurements from the CFHTLenS and Planck+WMAP polarization. We perform an independent analysis of the CFHTLenS six bin tomography results of Heymans et al. (2013). We extend their systematics treatment and find the cosmological constraints to be relatively robust to the choice of non-linear modeling, extension to the intrinsic alignment model and inclusion of baryons. We find that the 90% confidence contours of CFHTLenS and Planck+WP do not overlap even in the full 6-dimensional parameter space of $\Lambda$CDM, so the two datasets are discrepant. Allowing a massive active neutrino or tensor modes does not significantly resolve the disagreement in the full n-dimensional parameter space. Our results differ from some in the literature because we use the full tomographic information in the weak lensing data and marginalize over systematics. We note that adding a sterile neutrino to $\Lambda$CDM does bring the 8-dimensional 64% contours to overlap, mainly due to the extra effective number of neutrino species, which we find to be 0.84 $\pm$ 0.35 (68%) greater than standard on combining the datasets. We discuss why this is not a completely satisfactory resolution, leaving open the possibility of other new physics or observational systematics as contributing factors. We provide updated cosmology fitting functions for the CFHTLenS constraints and discuss the differences from ones used in the literature.Comment: 12 pages, 8 figures. We compare our findings with studies that include other low redshift probes of structure. An interactive figure is available at http://bit.ly/1oZH0KQ. This version is that accepted by MNRAS, and so includes changes based on the referee's comments, and updates to the analysis cod

Human routers:How Syrian refugee brokers build the infrastructure of displacement

Syrian refugees resort to a rich ecosystem of brokers who not only facilitate border crossings but also move remittances, jobs, knowledge, wives, and more. How are refugees' circulations made possible, and by whom? Drawing on fieldwork with Syrian brokers in Turkey and the United Kingdom, I put forward the novel concepts of a Syrian infrastructure of displacement and of refugee brokers as a particular infrastructural component, namely, as human routers. Like routers, brokers manage, direct, and control resource flows. Revisiting Julia Elyachar's concept of communicative channels, I contend that refugee brokers and their clients rely on such pre-existing connections, built on shared experiences of migration, brokerage, and hospitality. Reactivated in exile through brokers' performances of “Syrianness,” these channels facilitate a shared sense of belonging needed for their business transactions. The ways in which refugee brokers slip seamlessly between business, charitable deeds, and exploitation challenge the abstract ideas of disinterested solidarity that underpin mainstream humanitarianism

Gaussbock:Fast parallel-iterative cosmological parameter estimation with Bayesian nonparametrics

We present and apply Gaussbock, a new embarrassingly parallel iterative algorithm for cosmological parameter estimation designed for an era of cheap parallel computing resources. Gaussbock uses Bayesian nonparametrics and truncated importance sampling to accurately draw samples from posterior distributions with an orders-of-magnitude speed-up in wall time over alternative methods. Contemporary problems in this area often suffer from both increased computational costs due to high-dimensional parameter spaces and consequent excessive time requirements, as well as the need for fine tuning of proposal distributions or sampling parameters. Gaussbock is designed specifically with these issues in mind. We explore and validate the performance and convergence of the algorithm on a fast approximation to the Dark Energy Survey Year 1 (DES Y1) posterior, finding reasonable scaling behavior with the number of parameters. We then test on the full DES Y1 posterior using large-scale supercomputing facilities, and recover reasonable agreement with previous chains, although the algorithm can underestimate the tails of poorly-constrained parameters. Additionally, we discuss and demonstrate how Gaussbock recovers complex posterior shapes very well at lower dimensions, but faces challenges to perform well on such distributions in higher dimensions. In addition, we provide the community with a user-friendly software tool for accelerated cosmological parameter estimation based on the methodology described in this paper.Comment: 19 pages, 10 figures, accepted for publication in Ap

Dark Energy Survey Year 1 Results: Weak Lensing Shape Catalogues

We present two galaxy shape catalogues from the Dark Energy Survey Year 1 data set, covering 1500 deg^2 with a median redshift of 0.59. The catalogues cover two main fields: Stripe 82, and an area overlapping the South Pole Telescope survey region. We describe our data analysis process and in particular our shape measurement using two independent shear measurement pipelines, METACALIBRATION and IM3SHAPE. The METACALIBRATION catalogue uses a Gaussian model with an innovative internal calibration scheme, and was applied to riz bands, yielding 34.8M objects. The IM3SHAPE catalogue uses a maximum-likelihood bulge/disc model calibrated using simulations, and was applied to r-band data, yielding 21.9M objects. Both catalogues pass a suite of null tests that demonstrate their fitness for use in weak lensing science. We estimate the 1σ uncertainties in multiplicative shear calibration to be 0.013 and 0.025 for the METACALIBRATION and IM3SHAPE catalogues, respectively