264 research outputs found
Asymptotically flat spacetimes in 3D bigravity
We report that a class of three-dimensional bimetric theories contain
asymptotically flat solutions. These spacetimes can be cast in a set of
asymptotic conditions at null infinity which are preserved under the infinite
dimensional BMS group. Moreover, the algebra of the canonical generators
exhibits a central extension. The possibility that these solutions describe
regular black holes is also discussed.Comment: 6 page
Boundary dynamics of asymptotically flat 3D gravity coupled to higher spin fields
We construct a two-dimensional action principle invariant under a spin-three
extension of BMS group. Such a theory is obtained through a reduction of
Chern-Simons action with a boundary. This procedure is carried out by imposing
a set of boundary conditions obtained from asymptotically flat spacetimes in
three dimensions. When implementing part of this set, we obtain an analog of
chiral WZW model based on a contraction of . The remaining part of the boundary conditions imposes
constraints on the conserved currents of the model, which allows to further
reduce the action principle. It is shown that a sector of this latter theory is
related to a flat limit of Toda theory.Comment: 16 pages, no figure
Supertranslations and Superrotations at the Black Hole Horizon
We show that the asymptotic symmetries close to nonextremal black hole
horizons are generated by an extension of supertranslations. This group is
generated by a semidirect sum of Virasoro and Abelian currents. The charges
associated with the asymptotic Killing symmetries satisfy the same algebra.
When considering the special case of a stationary black hole, the zero mode
charges correspond to the angular momentum and the entropy at the horizon.Comment: 6 pages, references added, published versio
Causal inference under multiple versions of treatment
In this article we discuss the no-multiple-versions-of-treatment assumption and extend the potential outcomes framework to accommodate causal inference under violations of this assumption. A variety of examples are discussed in which the assumption may be violated. Identification results are provided for the overall treatment effect and the effect of treatment on the treated when multiple versions of treatment are present and also for the causal effect comparing a version of one treatment to some other version of the same or a different treatment. Further identification and interpretative results are given for cases in which a treatment variable is dichotomized to create a new treatment variable for which there are effectively multiple versions and also for effects defined by setting the version of treatment to a prespecified distribution. Some of the identification results bear resemblance to identification results in the literature on direct and indirect effects. We describe some settings in which ignoring multiple versions of treatment, even when present, will not lead to incorrect inferences
Host genotype interacts with aerial spore communities and influences the needle mycobiome of Norway spruce
The factors shaping the composition of the tree mycobiome are still under investigation. We tested the effects of host genotype, site, host phenotypic traits, and air fungal spore communities on the assembly of the fungi inhabiting Norway spruce needles. We used Norway spruce clones and spore traps within the collection sites and characterized both needle and air mycobiome communities by high-throughput sequencing of the ITS2 region. The composition of the needle mycobiome differed between Norway spruce clones, and clones with high genetic similarity had a more similar mycobiome. The needle mycobiome also varied across sites and was associated with the composition of the local air mycobiome and climate. Phenotypic traits such as diameter at breast height or crown health influenced the needle mycobiome to a lesser extent than host genotype and air mycobiome. Altogether, our results suggest that the needle mycobiome is mainly driven by the host genotype in combination with the composition of the local air spore communities. Our work highlights the role of host intraspecific variation in shaping the mycobiome of trees and provides new insights on the ecological processes structuring fungal communities inhabiting woody plants.This research was supported by the Swedish research council for Environment, Agricultural Sciences and Spatial Planning, FORMAS, project 2016-00798. M.E. and H.D.C were also supported by Formas project 2017-00402. J.O. was partially supported by the 'Ramon y Cajal' fellowship RYC-2015-17459. The authors would like to thank the owners of the seed orchards, Svenska skogsplantor AB and Sodra skogsagarna AB, for allowing us to sample the trees and assisting with the air mycobiome sampling. The authors also thank Antonio Rizzi, Rena Gadjieva, Maria Jonsson, and Katarina Ihrmark for their assistance with the laboratory and field work. The authors would like to acknowledge the support of the National Genomics Infrastructure (NGI)/Uppsala, Genome Center and UPPMAX for assisting us in massive parallel sequencing and computational infrastructure. Work performed at NGI/Uppsala Genome Center was funded by RFI/VR and Science for Life Laboratory, Sweden
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