4,093 research outputs found
A flow-based approach to rough differential equations
These are lecture notes for a Master 2 course on rough differential equations
driven by weak geometric Holder p-rough paths, for any p>2. They provide a
short, self-contained and pedagogical account of the theory, with an emphasis
on flows. The theory is illustrated by some now classical applications to
stochastic analysis, such as the basics of Freidlin-Wentzel theory of large
deviations for diffusions, or Stroock and Varadhan support theorem.Comment: 63 page
Subdyadic square functions and applications to weighted harmonic analysis
Through the study of novel variants of the classical Littlewood-Paley-Stein
-functions, we obtain pointwise estimates for broad classes of
highly-singular Fourier multipliers on satisfying regularity
hypotheses adapted to fine (subdyadic) scales. In particular, this allows us to
efficiently bound such multipliers by geometrically-defined maximal operators
via general weighted inequalities, in the spirit of a well-known
conjecture of Stein. Our framework applies to solution operators for dispersive
PDE, such as the time-dependent free Schr\"odinger equation, and other highly
oscillatory convolution operators that fall well beyond the scope of the
Calder\'on-Zygmund theory.Comment: To appear in Advances in Mathematic
Coxeter Groups and Wavelet Sets
A traditional wavelet is a special case of a vector in a separable Hilbert
space that generates a basis under the action of a system of unitary operators
defined in terms of translation and dilation operations. A
Coxeter/fractal-surface wavelet is obtained by defining fractal surfaces on
foldable figures, which tesselate the embedding space by reflections in their
bounding hyperplanes instead of by translations along a lattice. Although both
theories look different at their onset, there exist connections and
communalities which are exhibited in this semi-expository paper. In particular,
there is a natural notion of a dilation-reflection wavelet set. We prove that
dilation-reflection wavelet sets exist for arbitrary expansive matrix
dilations, paralleling the traditional dilation-translation wavelet theory.
There are certain measurable sets which can serve simultaneously as
dilation-translation wavelet sets and dilation-reflection wavelet sets,
although the orthonormal structures generated in the two theories are
considerably different
Paley-Littlewood decomposition for sectorial operators and interpolation spaces
We prove Paley-Littlewood decompositions for the scales of fractional powers
of -sectorial operators on a Banach space which correspond to
Triebel-Lizorkin spaces and the scale of Besov spaces if is the classical
Laplace operator on We use the -calculus,
spectral multiplier theorems and generalized square functions on Banach spaces
and apply our results to Laplace-type operators on manifolds and graphs,
Schr\"odinger operators and Hermite expansion.We also give variants of these
results for bisectorial operators and for generators of groups with a bounded
-calculus on strips.Comment: 2nd version to appear in Mathematische Nachrichten, Mathematical News
/ Mathematische Nachrichten, Wiley-VCH Verlag, 201
- …