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  1. Abstract

    Numerical solutions to the Einstein constraint equations are constructed on a selection of compact orientable three-dimensional manifolds with non-trivial topologies. A simple constant mean curvature solution and a somewhat more complicated non-constant mean curvature solution are computed on example manifolds from three of the eight Thursten geometrization classes. The constant mean curvature solutions found here are also solutions to the Yamabe problem that transforms a geometry into one with constant scalar curvature.

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  2. Abstract

    We report on a search for continuous gravitational waves (GWs) from NS 1987A, the neutron star born in SN 1987A. The search covered a frequency band of 75–275 Hz, included a wide range of spin-down parameters for the first time, and coherently integrated 12.8 days of LIGO data below 125 Hz and 8.7 days of LIGO data above 125 Hz from the second Advanced LIGO–Virgo observing run. We found no astrophysical signal. We set upper limits on GW emission as tight as an intrinsic strain of 2 × 10−25at 90% confidence. The large spin-down parameter space makes this search the first astrophysically consistent one for continuous GWs from NS 1987A. Our upper limits are the first consistent ones to beat an analog of the spin-down limit based on the age of the neutron star and hence are the first GW observations to put new constraints on NS 1987A.

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  3. Lu, Guozhen (Ed.)
    The study of certain differential operators between Sobolev spaces of sections of vector bundles on compact manifolds equipped with rough metric is closely related to the study of locally Sobolev functions on domains in the Euclidean space. In this paper, we present a coherent rigorous study of some of the properties of locally Sobolev-Slobodeckij functions that are especially useful in the study of differential operators between sections of vector bundles on compact manifolds with rough metric. The results of this type in published literature generally can be found only for integer order Sobolev spaces W m , p or Bessel potential spaces H s . Here, we have presented the relevant results and their detailed proofs for Sobolev-Slobodeckij spaces W s , p where s does not need to be an integer. We also develop a number of results needed in the study of differential operators on manifolds that do not appear to be in the literature. 
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  4. The study of Einstein constraint equations in general relativity naturally leads to considering Riemannian manifolds equipped with nonsmooth metrics. There are several important differential operators on Riemannian manifolds whose definitions depend on the metric: gradient, divergence, Laplacian, covariant derivative, conformal Killing operator, and vector Laplacian, among others. In this article, we study the approximation of such operators, defined using a rough metric, by the corresponding operators defined using a smooth metric. This paves the road to understanding to what extent the nice properties such operators possess, when defined with smooth metric, will transfer over to the corresponding operators defined using a nonsmooth metric. These properties are often assumed to hold when working with rough metrics, but to date the supporting literature is slim. 
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  5. In this manuscript, we present a coherent rigorous overview of the main properties of Sobolev-Slobodeckij spaces of sections of vector bundles on compact manifolds; results of this type are scattered through the literature and can be difficult to find. A special emphasis has been put on spaces with noninteger smoothness order, and a special attention has been paid to the peculiar fact that for a general nonsmooth domain Ω in Rn, 0 more » « less