arXiv subjects
Publications and source records attributed to Ryan McConnell.
We utilize a modulation restricted normal form approach to establish local well-posedness of the periodic Korteweg-de Vries equation in $H^s(\mathbb{T})$ for $s> -\frac23$. This work creates an analogue of the mKdV result by Nakanishi, Takaoka, and Tsutsumi for KdV, extending the currently best-known result of $s \geq -\frac12$ without utilizing the theory of complete integrability.
We prove and utilize an improvement to the short time estimates of Burq, G\'erard, & Tzvetkov on $\mathbb{T}$ via connecting this estimate to the number of lattice points in thin annuli. As a consequence, we enhance the well-posedness level of the periodic quintic Nonlinear Schr\"odinger equation to $s > \frac{131}{624}\sim 0.21$, which is an improvement on the results of De Silva, Pavlovi\'c, Staffilani, & Tzirakis, Li, Wu, & Xu, and Schippa. We also present conditional results, dependent on improvements on the count of lattice points in thin annuli.
We study well-posedness for a non-integrable generalization of the fifth order KdV, the second member in the KdV heirarchy. In particular, we use differentiation-by-parts to establish well-posedness for $s> 35/64$ in low modulation restricted norm spaces, as well as non-linear smoothing of order $\varepsilon < \min(2(s-35/64), 1)$. As corollaries, we obtain unconditional well-posedness for the non-integrable fifth order KdV for $s > 1$ and global well-posedness for the integrable fifth order KdV for $s\geq 1$. We also show local well-posedness for the non-integrable fifth order KdV for $s > 1/2$, contingent upon the conjectured $L^8$ Strichartz estimate. As an application of the nonlinear smoothing we obtain non-trivial upper bounds on the upper Minkowski dimension of the solution to the non-integrable fifth order KdV.
We utilize exponential sum techniques to obtain upper and lower bounds for the fractal dimension of the graph of solutions to the linear Schrödinger equation on $\mathbb{S}^d$ and $\mathbb{T}^d$. Specifically for $\mathbb S^d$, we provide dimension bounds using both $L^p$ estimates of Littlewood-Paley blocks, as well as assumptions on the Fourier coefficients. In the appendix, we present a slight improvement to the bilinear Strichartz estimate on $\mathbb{S}^2$ for functions supported on the zonal harmonics. We apply this to demonstrate an improved local well-posedness result for the zonal cubic NLS when $d=2$, and a nonlinear smoothing estimate when $d\geq 2$. As a corollary of the nonlinear smoothing for solutions to the zonal cubic NLS, we find dimension bounds generalizing the results of the first author and Tzirakis for solutions to the cubic NLS on $\mathbb{T}$. Additionally, we obtain several results on $\mathbb{T}^d$ generalizing the results of the $d=1$ case.
We consider the periodic non-linear Schrödinger equation with non-linearity given by $|u|^{p-1}u$ for odd $p > 1$ in dimension $1$. We first establish that the difference between the non-linear evolution and a phase rotation of the the linear evolution is in a smoother space. We then study forced and damped defocusing non-linear Schrödinger equations of the above type and establish an analogous smoothing statement that extends globally in time. As a corollary we establish both existence and smootheness for global attractors in the energy space.
We establish a smoothing result for the generalized KdV (gKdV) on the torus with polynomial non-linearity, damping, and forcing that matches the smoothing level for the gKdV at $H^1$. As a consequence, we establish the existence of a global attractor for this equation as well as its compactness in $H^s(\mathbb{T})$, $s\in (1,2).$