253 research outputs found
The decoupling limit of Multi-Gravity: Multi-Galileons, Dualities and More
In this paper we investigate the decoupling limit of a particular class of
multi-gravity theories, i.e. of theories of interacting spin-2 fields. We
explicitly compute the interactions of helicity-0 modes in this limit, showing
that they take on the form of multi-Galileons and dual forms. In the process we
extend the recently discovered Galileon dualities, deriving a set of new
multi-Galileon dualities. These are also intrinsically connected to healthy,
but higher-derivative, multi-scalar field theories akin to `beyond Horndeski'
models.Comment: 41 pages, 2 figure
Strong-coupling scales and the graph structure of multi-gravity theories
In this paper we consider how the strong-coupling scale, or perturbative
cutoff, in a multi-gravity theory depends upon the presence and structure of
interactions between the different fields. This can elegantly be rephrased in
terms of the size and structure of the `theory graph' which depicts the
interactions in a given theory. We show that the question can be answered in
terms of the properties of various graph-theoretical matrices, affording an
efficient way to estimate and place bounds on the strong-coupling scale of a
given theory. In light of this we also consider the problem of relating a given
theory graph to a discretised higher dimensional theory, a la dimensional
deconstruction.Comment: 23 pages, 7 figures; v2: additional references included, and minor
typos corrected; version published in JHE
de Sitter Branes in a Flat Bulk of Massive Gravity
We construct de Sitter branes in a flat bulk of massive gravity in . We
find two branches of solutions, reminiscent of the normal and self-accelerating
branches in DGP, but with rather different properties. Neither branch has a
self-accelerating limit: the background geometry requires having a nonvanishing
tension. On the other hand, on both branches there are sub-branches where the
leading order contributions of the tension to the curvature cancel. In these
cases it turns out that larger tensions curve the background less. Further,
both branches support a localized massless graviton for a special choice
of bulk mass terms. This choice may be protected by enhanced gauge symmetry at
least at the linearized level. Finally, we generalize the solutions to the case
of bigravity in a flat bulk.Comment: 19 pages LaTeX, one .pdf figure; v2 expanded discussion on possible
ghost-freedom of the construction, and other minor changes to agree with
published versio
SiTAR: Situated Trajectory Analysis for In-the-Wild Pose Error Estimation
Virtual content instability caused by device pose tracking error remains a
prevalent issue in markerless augmented reality (AR), especially on smartphones
and tablets. However, when examining environments which will host AR
experiences, it is challenging to determine where those instability artifacts
will occur; we rarely have access to ground truth pose to measure pose error,
and even if pose error is available, traditional visualizations do not connect
that data with the real environment, limiting their usefulness. To address
these issues we present SiTAR (Situated Trajectory Analysis for Augmented
Reality), the first situated trajectory analysis system for AR that
incorporates estimates of pose tracking error. We start by developing the first
uncertainty-based pose error estimation method for visual-inertial simultaneous
localization and mapping (VI-SLAM), which allows us to obtain pose error
estimates without ground truth; we achieve an average accuracy of up to 96.1%
and an average F1 score of up to 0.77 in our evaluations on four VI-SLAM
datasets. Next we present our SiTAR system, implemented for ARCore devices,
combining a backend that supplies uncertainty-based pose error estimates with a
frontend that generates situated trajectory visualizations. Finally, we
evaluate the efficacy of SiTAR in realistic conditions by testing three
visualization techniques in an in-the-wild study with 15 users and 13 diverse
environments; this study reveals the impact both environment scale and the
properties of surfaces present can have on user experience and task
performance.Comment: To appear in Proceedings of IEEE ISMAR 202
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