1,124 research outputs found
Jackiw-Pi Model: A Superfield Approach
We derive the off-shell nilpotent and absolutely anticommuting
Becchi-Rouet-Stora-Tyutin (BRST) as well as anti-BRST transformations s_{(a)b}
corresponding to the Yang-Mills gauge transformations of 3D Jackiw-Pi model by
exploiting the "augmented" superfield formalism. We also show that the
Curci-Ferrari restriction, which is a hallmark of any non-Abelian 1-form gauge
theories, emerges naturally within this formalism and plays an instrumental
role in providing the proof of absolute anticommutativity of s_{(a)b}.Comment: LaTeX file, 6 pages, Talk delivered at SQS'2013 (BLTP, JINR, Dubna,
Russia
Novel Symmetries in Vector Schwinger Model
We derive nilpotent and absolutely anticommuting (anti-)co-BRST symmetry
transformations for the bosonized version of (1+1)-dimensional (2D) vector
Schwinger model. These symmetry transformations turn out to be the analogue of
co-exterior derivative of differential geometry as the total gauge-fixing term
remains invariant under it. The exterior derivative is realized in terms of the
(anti-)BRST symmetry transformations of the theory whereas the bosonic
symmetries find their analogue in the Laplacian operator. The algebra obeyed by
these symmetry transformations turns out to be exactly same as the algebra
obeyed by the de Rham cohomological operators of differential geometry.Comment: LaTeX file, 12+1 pages, no figures, typos fixed, references expanded,
text modified, version to appear in MPL
Learning Exploration Policies for Navigation
Numerous past works have tackled the problem of task-driven navigation. But,
how to effectively explore a new environment to enable a variety of down-stream
tasks has received much less attention. In this work, we study how agents can
autonomously explore realistic and complex 3D environments without the context
of task-rewards. We propose a learning-based approach and investigate different
policy architectures, reward functions, and training paradigms. We find that
the use of policies with spatial memory that are bootstrapped with imitation
learning and finally finetuned with coverage rewards derived purely from
on-board sensors can be effective at exploring novel environments. We show that
our learned exploration policies can explore better than classical approaches
based on geometry alone and generic learning-based exploration techniques.
Finally, we also show how such task-agnostic exploration can be used for
down-stream tasks. Code and Videos are available at:
https://sites.google.com/view/exploration-for-nav
Visual Semantic Role Labeling
In this paper we introduce the problem of Visual Semantic Role Labeling:
given an image we want to detect people doing actions and localize the objects
of interaction. Classical approaches to action recognition either study the
task of action classification at the image or video clip level or at best
produce a bounding box around the person doing the action. We believe such an
output is inadequate and a complete understanding can only come when we are
able to associate objects in the scene to the different semantic roles of the
action. To enable progress towards this goal, we annotate a dataset of 16K
people instances in 10K images with actions they are doing and associate
objects in the scene with different semantic roles for each action. Finally, we
provide a set of baseline algorithms for this task and analyze error modes
providing directions for future work
Nilpotent Symmetries in Jackiw-Pi Model: Augmented Superfield Approach
We derive the complete set of off-shell nilpotent (s^2_{(a)b} = 0) and
absolutely anticommuting (s_b s_{ab} + s_{ab} s_b = 0)
Becchi-Rouet-Stora-Tyutin (BRST) (s_b) as well as anti-BRST symmetry
transformations (s_{ab}) corresponding to the combined Yang-Mills and
non-Yang-Mills symmetries of the (2 + 1)-dimensional Jackiw-Pi model within the
framework of augmented superfield formalism. The absolute anticommutativity of
the (anti-)BRST symmetries is ensured by the existence of two sets of
Curci-Ferrari (CF) type of conditions which emerge naturally in this formalism.
The presence of CF conditions enables us to derive the coupled but equivalent
Lagrangian densities. We also capture the (anti-)BRST invariance of the coupled
Lagrangian densities in the superfield formalism. The derivation of the
(anti-)BRST transformations of the auxiliary field \rho is one of the key
findings which can neither be generated by the nilpotent (anti-)BRST charges
nor by the requirements of the nilpotency and/or absolute anticommutativity of
the (anti-)BRST transformations. Finally, we provide a bird's-eye view on the
role of auxiliary field for various massive models and point out few striking
similarities and some glaring differences among them.Comment: LaTex file: 24 pages, no figures, minor modifications in the title
and text, references expanded, version to appear in IJT
Augmented Superfield Approach to Non-Yang-Mills Symmetries of Jackiw-Pi Model: Novel Observations
We derive the off-shell nilpotent and absolutely anticommuting
Becchi-Rouet-Stora-Tyutin (BRST) as well as anti-BRST symmetry transformations
corresponding to the non-Yang-Mills symmetry transformations of (2 + 1)-
dimensional Jackiw-Pi (JP) model within the framework of "augmented" superfield
formalism. The Curci-Ferrari restriction, which is a hallmark of non-Abelian
1-form gauge theories, does not appear in this case. One of the novel features
of our present investigation is the derivation of proper (anti-)BRST symmetry
transformations corresponding to the auxiliary field \rho that can not be
derived by any conventional means.Comment: LaTeX file, 17 pages, journal version, typos fixed, references
modifie
Anti Self-Dual Yang-Mills, Modified Faddeev-Jackiw Formalism and Hidden BRS Invariance
We analyze the constraints for a system of anti self-dual Yang-Mills (ASDYM)
equations by means of the modified Faddeev-Jackiw method in K and J gauges
\`{a} la Yang. We also establish the Hamiltonian flow for ASDYM system through
the hidden BRS invariance in both the gauges. Finally, we remark on the
bi-Hamiltonian nature of ASDYM and the compatibility of the symplectic
structures therein.Comment: Typos fixed, revised version accepted for publicatio
Canonical brackets from continuous symmetries: Abelian 2-form gauge theory
We derive the canonical (anti-)commutation relations amongst the creation and
annihilation operators of the various basic fields, present in the four (3 +
1)-dimensional (4D) free Abelian 2-from gauge theory, with the help of
continuous symmetry transformations within the framework of
Becchi-Rouet-Stora-Tyutin (BRST) formalism. We show that all the six continuous
symmetries of the theory lead to the exactly the same non-vanishing
(anti-)commutator amongst the creation and annihilation operators of the normal
mode expansion of the basic fields of the theory.Comment: LaTeX file, 16 pages, No figure
Exploring Person Context and Local Scene Context for Object Detection
In this paper we explore two ways of using context for object detection. The
first model focusses on people and the objects they commonly interact with,
such as fashion and sports accessories. The second model considers more general
object detection and uses the spatial relationships between objects and between
objects and scenes. Our models are able to capture precise spatial
relationships between the context and the object of interest, and make
effective use of the appearance of the contextual region. On the newly released
COCO dataset, our models provide relative improvements of up to 5% over
CNN-based state-of-the-art detectors, with the gains concentrated on hard cases
such as small objects (10% relative improvement)
Learning Navigation Subroutines from Egocentric Videos
Planning at a higher level of abstraction instead of low level torques
improves the sample efficiency in reinforcement learning, and computational
efficiency in classical planning. We propose a method to learn such
hierarchical abstractions, or subroutines from egocentric video data of experts
performing tasks. We learn a self-supervised inverse model on small amounts of
random interaction data to pseudo-label the expert egocentric videos with agent
actions. Visuomotor subroutines are acquired from these pseudo-labeled videos
by learning a latent intent-conditioned policy that predicts the inferred
pseudo-actions from the corresponding image observations. We demonstrate our
proposed approach in context of navigation, and show that we can successfully
learn consistent and diverse visuomotor subroutines from passive egocentric
videos. We demonstrate the utility of our acquired visuomotor subroutines by
using them as is for exploration, and as sub-policies in a hierarchical RL
framework for reaching point goals and semantic goals. We also demonstrate
behavior of our subroutines in the real world, by deploying them on a real
robotic platform. Project website:
https://ashishkumar1993.github.io/subroutines/
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