Non-existence and instantaneous extinction of solutions for singular nonlinear fractional diffusion equations

TL;DR

This paper proves the non-existence and instantaneous extinction of solutions for certain singular nonlinear fractional diffusion equations, establishing optimal conditions for non-existence in various dimensions and extending results to related elliptic problems.

Contribution

It demonstrates non-existence of solutions for fractional diffusion equations with very singular nonlinearities, including specific cases and generalizations, in multiple dimensions.

Findings

No solutions for certain singular nonlinearities in dimensions ≥ 2.

Optimal non-existence conditions depending on parameters s and n.

Extension of non-existence results to related elliptic equations.

Abstract

We show non-existence of solutions of the Cauchy problem in $\mathbb{R}^N$ for the nonlinear parabolic equation involving fractional diffusion $\partial_t u + (-\Delta)^s \phi(u)= 0,$ with $0<s<1$ and very singular nonlinearities $\phi$ . More precisely, we prove that when $\phi(u)=-1/u^n$ with $n>0$, or $\phi(u) = \log u$, and we take nonnegative $L^1$ initial data, there is no (nonnegative) solution of the problem in any dimension $N\ge 2$. We find the range of non-existence when $N=1$ in terms of $s$ and $n$. The range of exponents that we find for non-existence both for parabolic and elliptic equations are optimal. Non-existence is then proved for more general nonlinearities $\phi$, and it is also extended to the related elliptic problem of nonlinear nonlocal type: $u + (-\Delta)^s \phi(u) = f$ with the same type of nonlinearity $\phi$.