Research projects

本研究課題では，変分構造を持つ非線形楕円型方程式に対し，解の存在や解の性質を明らかにすることを目標にしている．本課題で扱う非線形楕円型方程式は物理学や幾何学において現れ，解の存在やその性質を調べることは重要であるが，解の陽的な表示を得ることは非常に難しく，ほとんど不可能であるように思える．そのため解の陽的な表示を使わずに特定の性質を持った解の存在を示したり，解があったとすると特定の性質を必ず持つ，ということを明らかにしたい．

The aim of this research project was to investigate the structure of nontrivial solutions to elliptic equations involving singularities, nonlocalities and so on. During the period, the following results were obtained. For the Born-Infeld equation(this equation has a singularity), the regularity of minimizer as well as the relation between minimizers and weak solutions were studied. For the equation with the fractional Laplacian and the Hardy-Henon type nonlinearity (the equation has a nonlocality), the existence and nonexistence of stables solutions was proved. The layer property of the family of stable solutions were also shown. In addition to these two equations, the existence of nontrivial solutions and their properties were obtained for the equation with sublinear nonlinearities, a class of equations involving the 1 dimensional Pucci operators, the equation with large parameters and the equation with a constraint on the L^2 norm of solutions.

Solution structures, which are bifurcation diagrams, of supercritical elliptic Dirichlet problem are studied. It is known that standard variational approaches, which are used to study subcritical problems, are not applicable to supercritical problems. A large part of a solution structure was not known. In this study we consider positive solutions of elliptic Dirichlet problem when the domain is a ball. We show that a positive radial singular solution of the supercritical elliptic equation plays a crucial role in the study of bifurcation diagrams. We prove the existence and uniqueness of a positive radial singular solution and obtain an asymptotic expansion of the singular solution near the singular point. We apply our theory to several interesting elliptic equations and classify the bifurcation diagrams.

Nonlinear dispersive partial differential equation is one of important class in the partial differential equations. Due to a complex interaction between dispersive and nonlinear effects in the equation, there is a wide variety of asymptotic behavior of solution, and it is difficult to study long time behavior of solution. In this research, we tried to gain a new insight on long time behavior of solution to nonlinear dispersive equation by analyzing concrete models via harmonic analysis and variational methods.

In this project, the existence of solutions and their properties were studied for nonlinear elliptic partial differential equations. In particular, we treated equations which have variational structure (for instance, equations with fractional operators of elliptic operators). We proved the existence of solutions satisfying some properties and showed the existence of multiple solutions. We also studied a variant of the Trudinger-Moser inequality and found conditions when the inequality is satisfied as an equality. This inequality is related to a certain nonlinear elliptic partial differential equation.