Special Session 131: Recent progress on singularities formations of some evolution partial differential equations

Nonlinear wave equations in Cosmology: Some results, but mostly open problems

Jean-Pierre Eckmann
University of Geneva
Switzerland
Co-Author(s):    Farbod Hassani, Hatem Za`ag
Abstract:
In certain cosmological models (effective field theories) one encounters a non-linear wave equation of the form $$ u_{tt}=\alpha u_{xx} + \beta (u_x)^2 $$ with $\alpha>0$ and $\beta>0$ in $\ge 1$ dimension. While cosmologists believed that solutions stay bounded for large enough $\alpha$, it has been known for some time that nontrivial initial conditions lead to divergence in finite time. After explaining some of these results, I will focus also on the scaling of the diverging solutions. (For the experts: In the cosmological context, one is not allowed to scale the initial condition, since it is given by background conditions.)