31,180 research outputs found
The Background Field Method and the Linearization Problem for Poisson Manifolds
The background field method (BFM) for the Poisson Sigma Model (PSM) is
studied as an example of the application of the BFM technique to open gauge
algebras. The relationship with Seiberg-Witten maps arising in non-commutative
gauge theories is clarified. It is shown that the implementation of the BFM for
the PSM in the Batalin-Vilkovisky formalism is equivalent to the solution of a
generalized linearization problem (in the formal sense) for Poisson structures
in the presence of gauge fields. Sufficient conditions for the existence of a
solution and a constructive method to derive it are presented.Comment: 33 pp. LaTex, references and comments adde
No Dynamics in the Extremal Kerr Throat
Motivated by the Kerr/CFT conjecture, we explore solutions of vacuum general
relativity whose asymptotic behavior agrees with that of the extremal Kerr
throat, sometimes called the Near-Horizon Extreme Kerr (NHEK) geometry. We
argue that all such solutions are diffeomorphic to the NHEK geometry itself.
The logic proceeds in two steps. We first argue that certain charges must
vanish at all times for any solution with NHEK asymptotics. We then analyze
these charges in detail for linearized solutions. Though one can choose the
relevant charges to vanish at any initial time, these charges are not
conserved. As a result, requiring the charges to vanish at all times is a much
stronger condition. We argue that all solutions satisfying this condition are
diffeomorphic to the NHEK metric.Comment: 42 pages, 3 figures. v3: minor clarifications and correction
Dynamical complexity of the Brans-Dicke cosmology
The dynamics of the Brans-Dicke theory with a quadratic scalar field
potential function and barotropic matter is investigated. The dynamical system
methods are used to reveal complexity of dynamical evolution in homogeneous and
isotropic cosmological models. The structure of phase space crucially depends
on the parameter of the theory as well as barotropic
matter index . In our analysis these parameters are treated as
bifurcation parameters. We found sets of values of these parameters which lead
to generic evolutional scenarios. We show that in isotropic and homogeneous
models in the Brans-Dicke theory with a quadratic potential function the de
Sitter state appears naturally. Stability conditions of this state are fully
investigated. It is shown that these models can explain accelerated expansion
of the Universe without the assumption of the substantial form of dark matter
and dark energy. The Poincare construction of compactified phase space with a
circle at infinity is used to show that phase space trajectories in a physical
region can be equipped with a structure of a vector field on nontrivial
topological closed space. For we show new types of
early and late time evolution leading from the anti-de Sitter to the de Sitter
state through an asymmetric bounce. In the theory without a ghost we find
bouncing solutions and the coexistence of the bounces and the singularity.
Following the Peixoto theorem some conclusions about structural stability are
drawn.Comment: 34 pages, 14 figs; (v2) 36 pages, 16 figs, refs. added, JCAP (in
press
Long time dynamics and coherent states in nonlinear wave equations
We discuss recent progress in finding all coherent states supported by
nonlinear wave equations, their stability and the long time behavior of nearby
solutions.Comment: bases on the authors presentation at 2015 AMMCS-CAIMS Congress, to
appear in Fields Institute Communications: Advances in Applied Mathematics,
Modeling, and Computational Science 201
Structured Linearization of Discrete Mechanical Systems for Analysis and Optimal Control
Variational integrators are well-suited for simulation of mechanical systems
because they preserve mechanical quantities about a system such as momentum, or
its change if external forcing is involved, and holonomic constraints. While
they are not energy-preserving they do exhibit long-time stable energy
behavior. However, variational integrators often simulate mechanical system
dynamics by solving an implicit difference equation at each time step, one that
is moreover expressed purely in terms of configurations at different time
steps. This paper formulates the first- and second-order linearizations of a
variational integrator in a manner that is amenable to control analysis and
synthesis, creating a bridge between existing analysis and optimal control
tools for discrete dynamic systems and variational integrators for mechanical
systems in generalized coordinates with forcing and holonomic constraints. The
forced pendulum is used to illustrate the technique. A second example solves
the discrete LQR problem to find a locally stabilizing controller for a 40 DOF
system with 6 constraints.Comment: 13 page
Structured Linearization of Discrete Mechanical Systems for Analysis and Optimal Control
Variational integrators are well-suited for simulation of mechanical systems
because they preserve mechanical quantities about a system such as momentum, or
its change if external forcing is involved, and holonomic constraints. While
they are not energy-preserving they do exhibit long-time stable energy
behavior. However, variational integrators often simulate mechanical system
dynamics by solving an implicit difference equation at each time step, one that
is moreover expressed purely in terms of configurations at different time
steps. This paper formulates the first- and second-order linearizations of a
variational integrator in a manner that is amenable to control analysis and
synthesis, creating a bridge between existing analysis and optimal control
tools for discrete dynamic systems and variational integrators for mechanical
systems in generalized coordinates with forcing and holonomic constraints. The
forced pendulum is used to illustrate the technique. A second example solves
the discrete LQR problem to find a locally stabilizing controller for a 40 DOF
system with 6 constraints.Comment: 13 page
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