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James Dilts

Publications and source records attributed to James Dilts.

8 recordsLinked to original sources
arXiv2018

Numerical Bifurcation Analysis of the Conformal Method

The conformal formulation of the Einstein constraint equations has been studied intensively since the modern version of the conformal method was first pub- lished in the early 1970s. Proofs of existence and uniqueness of solutions were limited to the constant mean curvature (CMC) case through the early 90s, with analogous results for the near-CMC case beginning to appear thereafter. In the last decade, there has been some limited progress towards understanding the properties of the conformal method for far-from-CMC solutions as well. Although it was initially conceivable that that these far-from-CMC results would lead to a solution theory for the non-CMC case that would mirror the good properties of the CMC and near-CMC cases, examples of bifurcations and of nonexistence of solutions have been since discovered. Nevertheless, the general properties of the conformal method for far-from-CMC data remain unknown. In this article we apply analytic and numerical continuation techniques to the study of the con- formal method, in an attempt to give some insight into what the solution behavior is in the far-from-CMC case in various scenarios.

gr-qc↗
arXiv2017

When Do Spacetimes Have Constant Mean Curvature Slices?

Many results in mathematical relativity, including results for both the initial data problem and for the evolution problem, rely on the existence of a constant mean curvature (CMC) Cauchy surface in the underlying spacetime. However, it is known that some spacetimes have no CMC Cauchy surfaces (slices). This is an obstacle for many results and constructions with these types of spacetimes, and is particularly worrisome since it is not known whether spacetimes that do have CMC slices are in any sense generic. In this expository paper, we will discuss the known results about the existence (and non-existence) of CMC slices, examine the evidence for cases which are unknown, and make several conjectures concerning the existence of CMC slices and their generality.

gr-qc↗
arXiv2016

Existence and Blowup Results for Asymptotically Euclidean Initial Data Sets Generated by the Conformal Method

For each set of (freely chosen) seed data, the conformal method reduces the Einstein constraint equations to a system of elliptic equations, the conformal constraint equations. We prove an admissibility criterion, based on a (conformal) prescribed scalar curvature problem, which provides a necessary condition on the seed data for the conformal constraint equations to (possibly) admit a solution. We then consider sets of asymptotically Euclidean (AE) seed data for which solutions of the conformal constraint equations exist, and examine the blowup properties of these solutions as the seed data sets approach sets for which no solutions exist. We also prove that there are AE seed data sets which include a Yamabe nonpositive metric and lead to solutions of the conformal constraints. These data sets allow the mean curvature function to have zeroes.

gr-qc↗
arXiv2015

The Einstein Constraint Equations on Asymptotically Euclidean Manifolds

In this dissertation, we prove a number of results regarding the conformal method of finding solutions to the Einstein constraint equations. These results include necessary and sufficient conditions for the Lichnerowicz equation to have solutions, global supersolutions which guarantee solutions to the conformal constraint equations for near-constant-mean-curvature (near-CMC) data as well as for far-from-CMC data, a proof of the limit equation criterion in the near-CMC case, as well as a model problem on the relationship between the asymptotic constants of solutions and the ADM mass. We also prove a characterization of the Yamabe classes on asymptotically Euclidean manifolds and resolve the (conformally) prescribed scalar curvature problem on asymptotically Euclidean manifolds for the case of nonpositive scalar curvatures. Many, though not all, of the results in this dissertation have been previously published in [Dilts13b], [DIMM14], [DL14], [DM15], and [DGI15]. This article is the author's Ph.D. dissertation, except for a few minor changes.

gr-qc↗
arXiv2015

Yamabe Classification and Prescribed Scalar Curvature in the Asymptotically Euclidean Setting

We prove a necessary and sufficient condition for an asymptotically Euclidean manifold to be conformally related to one with specified nonpositive scalar curvature: the zero set of the desired scalar curvature must have a positive Yamabe invariant, as defined in the article. We show additionally how the sign of the Yamabe invariant of a measurable set can be computed from the sign of certain generalized "weighted" eigenvalues of the conformal Laplacian. Using the prescribed scalar curvature result we give a characterization of the Yamabe classes of asymptotically Euclidean manifolds. We also show that the Yamabe class of an asymptotically Euclidean manifold is the same as the Yamabe class of its conformal compactification.

math.DG↗
arXiv2014

The Einstein Constraint Equations on Compact Manifolds with Boundary

We continue the study of the Einstein constraint equations on compact manifolds with boundary initiated by Holst and Tsogtgerel. In particular, we consider the full system and prove existence of solutions in both the near-CMC and far-from-CMC (for Yamabe positive metrics) cases. We also make partial progress in proving the results of previous "limit equation" papers by Dahl, Gicquaud, Humbert and Sakovich.

gr-qc↗
arXiv2014

A limit equation criterion for applying the conformal method to asymptotically cylindrical initial data sets

We prove that in a certain class of conformal data on an asymptotically cylindrical manifold, if the conformally decomposed Einstein constraint equations do not admit a solution, then one can always find a nontrivial solution to the limit equation first explored by Dahl, Gicquaud, and Humbert in [DGH11]. We also give an example of a Ricci curvature condition on the manifold which precludes the existence of a solution to this limit equation, showing that such a limit criterion can be a useful tool for studying the Einstein constraint equations on manifolds with asymptotically cylindrical ends.

gr-qc↗