377 research outputs found
Correlation Functions of Warped CFT
Warped conformal field theory (WCFT) is a two dimensional quantum field
theory whose local symmetry algebra consists of a Virasoro algebra and a U(1)
Kac-Moody algebra. In this paper, we study correlation functions for primary
operators in WCFT. Similar to conformal symmetry, warped conformal symmetry is
very constraining. The form of the two and three point functions are determined
by the global warped conformal symmetry while the four point functions can be
determined up to an arbitrary function of the cross ratio. The warped conformal
bootstrap equation are constructed by formulating the notion of crossing
symmetry. In the large central charge limit, four point functions can be
decomposed into global warped conformal blocks, which can be solved exactly.
Furthermore, we revisit the scattering problem in warped AdS spacetime (WAdS),
and give a prescription on how to match the bulk result to a WCFT retarded
Green's function. Our result is consistent with the conjectured holographic
dualities between WCFT and WAdS.Comment: 20 pages, 0 figur
Gravitational waves in gauge theory gravity with a negative cosmological constant
In this paper, we discuss the gravitational waves in the context of gauge
theory gravity with a negative cosmological constant. The gauge theory gravity
is a gravity theory under gauge formulation in the language of geometric
algebra. In contrast to general relativity, the background spacetime in gauge
theory gravity is flat, the gauge freedom comes from the fact that equations in
terms of physical quantities should be kept in a covariant form under spacetime
displacements and rotations. Similar to the electromagnetism, the gauge
formulation enable us to interpret the gravitational force as a gauge force on
the background flat spacetime. The dynamical fields that describe the
gravitational interactions are those position and rotation gauge fields
introduced as the requirement of the gauge covariance. The gravitational field
equations can be derived from the least action principle with the action as a
gauge invariant quantity built from the covariant field strength. We discuss
the gravitational wave solutions of the field equations with a negative
cosmological constant, and show that the solution is of Petrov type-N. We also
discuss the velocity memory effect in the gauge theory gravity by calculating
the velocity change of an initially free falling massive particle after the
passing a gravitational impulsive wave.Comment: 31 pages, 3 figure
Auto-Encoding Scene Graphs for Image Captioning
We propose Scene Graph Auto-Encoder (SGAE) that incorporates the language
inductive bias into the encoder-decoder image captioning framework for more
human-like captions. Intuitively, we humans use the inductive bias to compose
collocations and contextual inference in discourse. For example, when we see
the relation `person on bike', it is natural to replace `on' with `ride' and
infer `person riding bike on a road' even the `road' is not evident. Therefore,
exploiting such bias as a language prior is expected to help the conventional
encoder-decoder models less likely overfit to the dataset bias and focus on
reasoning. Specifically, we use the scene graph --- a directed graph
() where an object node is connected by adjective nodes and
relationship nodes --- to represent the complex structural layout of both image
() and sentence (). In the textual domain, we use
SGAE to learn a dictionary () that helps to reconstruct sentences
in the pipeline, where encodes the desired language prior;
in the vision-language domain, we use the shared to guide the
encoder-decoder in the pipeline. Thanks to the scene graph
representation and shared dictionary, the inductive bias is transferred across
domains in principle. We validate the effectiveness of SGAE on the challenging
MS-COCO image captioning benchmark, e.g., our SGAE-based single-model achieves
a new state-of-the-art CIDEr-D on the Karpathy split, and a competitive
CIDEr-D (c40) on the official server even compared to other ensemble
models
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