19-7 Hongyu Cheng, Rafael de la Llave

Time dependent center manifold in PDEs (584K, PDF) Jan 23, 19

Abstract , Paper (src), View paper (auto. generated pdf), Index of related papers

Abstract. We consider externally forced evolution equations. Mathematically, these are skew systems driven by a finite dimensional evolution. Two very common cases included in our treatment are quasi-periodic forcing and forcing by a stochastic process. We allow that the evolution is a PDE and even that it is not well-posed and that it does not define an evolution (flow). We first establish a general abstract theorem which, under suitable (spectral, non-degeneracy, smoothness, etc) assumptions, establishes the existence of a ``time-dependent invariant manifold'' (TDIM). These manifolds evolve with the forcing. They are such that the original equation is always tangent to a vector field in the manifold. Hence, for initial data in the TDIM, the original equation is equivalent to an ordinary differential equation. This allows us to define families of solutions of the full equation by studying the solutions of a finite dimensional system. Note that this strategy may apply even if the original equation is ill posed and does not admit solutions for arbitrary initial conditions (the TDIM selects initial conditions for which solutions exist). It also allows that the TDIM is infinite dimensional. Secondly, we construct the center manifold for skew systems driven by the external forcing. Thirdly, we present concrete applications of the abstract result to the differential equations whose linear operators are exponential trichotomy subject to quasi-periodic perturbations. The use of TDIM allows us to establish the existence of quasi-periodic solutions and to study the effect of resonances.

Files: 19-7.src( 19-7.keywords , 2019-01-29-centermanifold.pdf.mm )