White noise for KdV and mKdV on the circle

We survey different approaches to study the invariance of the white noise for the periodic KdV. We mainly discuss the following two methods. First, we discuss the PDE method, following Bourgain \cite{BO4}, in a general framework. Then, we show how it can be applied to the low regularity setting of the white noise for KdV by introducing the Besov-type space \hat{b}^s_{p, \infty}, sp< -1. Secondly, we describe the probabilistic method by Quastel, Valk\'o, and the author \cite{OQV}. We also use this probabilistic approach to study the white noise for mKdV.Comment: 26 pages. To appear in RIMS Kokyuroku Bessats

On nonlinear Schr\"odinger equations with almost periodic initial data

We consider the Cauchy problem of nonlinear Schr\"odinger equations (NLS) with almost periodic functions as initial data. We first prove that, given a frequency set $\pmb{\omega} =\{\omega_j\}_{j = 1}^\infty$, NLS is local well-posed in the algebra $\mathcal{A}_{\pmb{\omega}}(\mathbb R)$ of almost periodic functions with absolutely convergent Fourier series. Then, we prove a finite time blowup result for NLS with a nonlinearity $|u|^p$, $p \in 2\mathbb{N}$. This elementary argument presents the first instance of finite time blowup solutions to NLS with generic almost periodic initial data.Comment: 18 pages. References updated. To appear in SIAM J. Math. Ana

Smoothing of commutators for a H\"ormander class of bilinear pseudodifferential operators

Commutators of bilinear pseudodifferential operators with symbols in the H\"ormander class BS_{1, 0}^1 and multiplication by Lipschitz functions are shown to be bilinear Calder\'on-Zygmund operators. A connection with a notion of compactness in the bilinear setting for the iteration of the commutators is also made.Comment: 16 page