2,213 research outputs found
Long-time asymptotics for fully nonlinear homogeneous parabolic equations
We study the long-time asymptotics of solutions of the uniformly parabolic
equation for a positively
homogeneous operator , subject to the initial condition ,
under the assumption that does not change sign and possesses sufficient
decay at infinity. We prove the existence of a unique positive solution
and negative solution , which satisfy the self-similarity
relations We prove that the rescaled limit of the solution of the Cauchy
problem with nonnegative (nonpositive) initial data converges to
() locally uniformly in . The anomalous exponents
and are identified as the principal half-eigenvalues of a
certain elliptic operator associated to in .Comment: 20 pages; revised version; two remarks added, typos and one minor
mistake correcte
Nonexistence of positive supersolutions of elliptic equations via the maximum principle
We introduce a new method for proving the nonexistence of positive
supersolutions of elliptic inequalities in unbounded domains of .
The simplicity and robustness of our maximum principle-based argument provides
for its applicability to many elliptic inequalities and systems, including
quasilinear operators such as the -Laplacian, and nondivergence form fully
nonlinear operators such as Bellman-Isaacs operators. Our method gives new and
optimal results in terms of the nonlinear functions appearing in the
inequalities, and applies to inequalities holding in the whole space as well as
exterior domains and cone-like domains.Comment: revised version, 32 page
Local asymptotics for controlled martingales
We consider controlled martingales with bounded steps where the controller is
allowed at each step to choose the distribution of the next step, and where the
goal is to hit a fixed ball at the origin at time . We show that the
algebraic rate of decay (as increases to infinity) of the value function in
the discrete setup coincides with its continuous counterpart, provided a
reachability assumption is satisfied. We also study in some detail the
uniformly elliptic case and obtain explicit bounds on the rate of decay. This
generalizes and improves upon several recent studies of the one dimensional
case, and is a discrete analogue of a stochastic control problem recently
investigated in Armstrong and Trokhimtchouck [Calc. Var. Partial Differential
Equations 38 (2010) 521-540].Comment: Published at http://dx.doi.org/10.1214/15-AAP1123 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Sharp Liouville results for fully nonlinear equations with power-growth nonlinearities
We study fully nonlinear elliptic equations such as in or in exterior domains, where is any uniformly elliptic,
positively homogeneous operator. We show that there exists a critical exponent,
depending on the homogeneity of the fundamental solution of , that sharply
characterizes the range of for which there exist positive supersolutions
or solutions in any exterior domain. Our result generalizes theorems of
Bidaut-V\'eron \cite{B} as well as Cutri and Leoni \cite{CL}, who found
critical exponents for supersolutions in the whole space , in case
is Laplace's operator and Pucci's operator, respectively. The arguments we
present are new and rely only on the scaling properties of the equation and the
maximum principle.Comment: 16 pages, new existence results adde
Regularity and stochastic homogenization of fully nonlinear equations without uniform ellipticity
We prove regularity and stochastic homogenization results for certain
degenerate elliptic equations in nondivergence form. The equation is required
to be strictly elliptic, but the ellipticity may oscillate on the microscopic
scale and is only assumed to have a finite th moment, where is the
dimension. In the general stationary-ergodic framework, we show that the
equation homogenizes to a deterministic, uniformly elliptic equation, and we
obtain an explicit estimate of the effective ellipticity, which is new even in
the uniformly elliptic context. Showing that such an equation behaves like a
uniformly elliptic equation requires a novel reworking of the regularity
theory. We prove deterministic estimates depending on averaged quantities
involving the distribution of the ellipticity, which are controlled in the
macroscopic limit by the ergodic theorem. We show that the moment condition is
sharp by giving an explicit example of an equation whose ellipticity has a
finite th moment, for every , but for which regularity and
homogenization break down. In probabilistic terms, the homogenization results
correspond to quenched invariance principles for diffusion processes in random
media, including linear diffusions as well as diffusions controlled by one
controller or two competing players.Comment: Published in at http://dx.doi.org/10.1214/13-AOP833 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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