Long-time behavior of solutions to the generalized Allen-Cahn model with degenerate diffusivity

TL;DR

This paper investigates the long-term behavior of solutions to a generalized Allen-Cahn equation with nonlinear, degenerate diffusion, showing that interface solutions persist for extended periods depending on specific parameters, with energy bounds derived for analysis.

Contribution

It introduces a detailed analysis of the long-time persistence of interface solutions in a generalized Allen-Cahn model with degenerate diffusivity, extending understanding of their stability over time.

Findings

Interface solutions persist for exponentially or algebraically long times.

Long-term behavior depends on the relationship between exponents m and n.

Energy bounds for a Ginzburg-Landau type potential are established.

Abstract

The generalized Allen-Cahn equation, \[ u_t=\varepsilon^2(D(u)u_x)_x-\frac{\varepsilon^2}2D'(u)u_x^2-F'(u), \] with nonlinear diffusion, $D = D(u)$, and potential, $F = F(u)$, of the form \[ D(u) = |1-u^2|^{m}, \quad \text{or} \quad D(u) = |1-u|^{m}, \quad m >1, \] and \[ F(u)=\frac{1}{2n}|1-u^2|^{n}, \qquad n\geq2, \] respectively, is studied. These choices correspond to a reaction function that can be derived from a double well potential, and to a generalized degenerate diffusivity coefficient depending on the density $u$ that vanishes at one or at the two wells, $u = \pm 1$. It is shown that interface layer solutions that are equal to $\pm 1$ except at a finite number of thin transitions of width $\varepsilon$ persist for an either exponentially or algebraically long time, depending upon the interplay between the exponents $n$ and $m$. For that purpose, energy bounds for a renormalized effective energy potential of Ginzburg-Landau type are derived.