Sign-changing solutions of the nonlinear heat equation with persistent singularities

Abstract

We study the existence of sign-changing solutions to the nonlinear heat equation $\partial _t u = Δu + |u|^αu$ on ${\mathbb R}^N $, $N\ge 3$, with $\frac {2} {N-2} < α<α_0$, where $α_0=\frac {4} {N-4+2\sqrt{ N-1 } }\in (\frac {2} {N-2}, \frac {4} {N-2})$, which are singular at $x=0$ on an interval of time. In particular, for certain $μ>0$ that can be arbitrarily large, we prove that for any $u_0 \in \mathrm{L} ^\infty _{\mathrm{loc}} ({\mathbb R}^N \setminus \{ 0 \}) $ which is bounded at infinity and equals $μ|x|^{- \frac {2} {α}}$ in a neighborhood of $0$, there exists a local (in time) solution $u$ of the nonlinear heat equation with initial value $u_0$, which is sign-changing, bounded at infinity and has the singularity $β|x|^{- \frac {2} {α}}$ at the origin in the sense that for $t>0$, $ |x|^{\frac {2} {α}} u(t,x) \to β$ as $ |x| \to 0$, where $β= \frac {2} {α} ( N -2 - \frac {2} {α} ) $. These solutions in general are neither stationary nor self-similar.