Arick Shao 邵崇哲

# Research / Notes

## Survey Notes

### A Brief Introduction to Mathematical Relativity

These notes, which grew from a short talk given at a postdoc lunch at Imperial College London in 2014, are intended as a brief introduction to the field of mathematical general relativity. The first part discusses the mathematics, in particular the geometry, behind Einstein's theory of special relativity. The second part expands the outlook toward the mathematics behind general relativity.

### Nonlinear Wave Equations

The following are portions of the lecture notes from a postgraduate course on dispersive equations that I co-taught (with Jonathan Ben-Artzi) in 2015. These chapters provide a first introduction to some landmark results on the study of nonlinear wave equations.

## Technical Notes

This section contains notes of a more technical nature, such as proofs or explanations of particular theorems or estimates.

### Notes on Carleman Estimates

The following are a further elaboration of some notes I had from a previous reading seminar I ran in 2019. These notes, which are heavily inspired by Nicolas Lerner's monograph on Carleman Equations, give a self-contained treatment and proof of Hörmander's classical Carleman estimate (from the microlocal point of view) and its application to unique continuation for PDEs.

(The newest version of the aims to be entirely self-contained. In particular, it now includes a proof of the sharp Gårding inequality, as well as a few additional microlocal analytic preliminaries.)

### The Method of Characteristics in PDEs

The following are supplementary notes on topics related to the method of characteristics, used in solving first-order PDEs. These were addenda to a postgraduate PDE module that I taught in 2015 while at Imperial College London.

### δ-Distributions in Dispersive Equations

These short notes discuss many of the manipulations involving δ-distributions and pullbacks through δ-distributions found in the study of dispersive equations. The goal is to explain in detail many points that are usually swept under the rug in the standard literature. As an application, we prove a basic bilinear estimate for solutions of the (free) Schrödinger equation.

### The Christ-Kiselev Lemma for Dispersive PDE

The Christ-Kiselev Lemma is a maximal-type estimate, which has important applications in dispersive partial differential equations. In particular, this estimate is an important tool in the application of Strichartz estimates.

Thanks to Yannis Angelopoulos for proofreading and corrections.

### Hörmander's Inequality for Wave Equations

These short notes contains a detailed account of the proof of Hörmander's inequality for wave equations in three spatial dimensions. This estimate played an essential role in establishing small data global existence for nonlinear wave equations satisfying the null condition.