Hans Christianson

  1. Near Sharp Strichartz estimates with loss in the presence of degenerate hyperbolic trapping.

    Authors: Hans Christianson
    Subjects: Analysis of PDEs
    Abstract

    We consider an $n$-dimensional spherically symmetric, asymptotically
    Euclidean manifold with two ends and a codimension 1 trapped set which is
    degenerately hyperbolic. By separating variables and constructing a
    semiclassical parametrix for a time scale polynomially beyond Ehrenfest time,
    we show that solutions to the linear Schr\"odiner equation with initial
    conditions localized on a spherical harmonic satisfy Strichartz estimates with
    a loss depending only on the dimension $n$ and independent of the degeneracy.
    The Strichartz estimates are sharp up to an arbitrary $\beta>0$ loss.

  2. Random walk on surfaces with hyperbolic cusps.

    Authors: Hans Christianson, Colin Guillarmou, Laurent Michel
    Subjects: Spectral Theory
    Abstract

    We consider the operator associated to a random walk on finite volume
    surfaces with hyperbolic cusps. We study the spectral gap (upper and lower
    bound) associated to this operator and deduce some rate of convergence of the
    iterated kernel towards its stationary distribution.

  3. Strichartz estimates for the water-wave problem with surface tension.

    Authors: Hans Christianson, Vera Mikyoung Hur, Gigliola Staffilani
    Subjects: Analysis of PDEs
    Abstract

    We study dispersive properties of one-dimensional surface water-waves under
    surface tension, based on the formulation of the problem as a nonlinear
    dispersive equation coupled with a transport-type equation. We establish a
    dispersion estimate on time scales depending on the size of the frequencies. We
    infer that, if $s$ is large enough, then a solution $u$ of the dispersive
    equation satisfies local-in-time weighted Strichartz estimates with loss in the
    admissibility condition:

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