# First-order linear evolution equations with c\`adl\`ag-in-time solutions

## TL;DR

This paper investigates first-order linear parabolic PDEs with measure-valued Fourier transforms, establishing existence, uniqueness, and cdl1g-in-time properties of solutions under various conditions, including pseudo-differential operators.

## Contribution

It introduces a framework for analyzing PDEs with measure-valued Fourier transforms, extending well-posedness and asymptotic analysis to cases with pseudo-differential spatial operators.

## Key findings

- Existence and uniqueness of solutions with cdl1g-in-time behavior.
- Solutions' Fourier transforms are slow-growing measures supported in +.
- Asymptotic convergence of solutions over long time periods.

## Abstract

In this work we study first-order linear parabolic evolution PDEs over $\mathbb{R}^{d}\times\mathbb{R}$ and $\mathbb{R}^{d}\times\mathbb{R}^{+}$ comprising a spatial operator defined through a symbol function and a source term such that its spatial Fourier transform is a slow-growing measure over $\mathbb{R}^{d}\times\mathbb{R}$. When the source term is required to has its support on $\mathbb{R}^{d}\times\mathbb{R}^{+}$, it is shown that there exists a unique solution such that its spatial Fourier transform is a slow-growing measure with support in $\mathbb{R}^{d}\times\mathbb{R}^{+}$, which in addition has a c\`adl\`ag-in-time behaviour. This allows to well-pose and analyse an initial value problem associated to this class of equations and to consider cases where the spatial operator can be a pseudo-differential operator. We also look at for solutions to the cases where the source term is such that its spatial and spatio-temporal Fourier transforms are slow-growing measures over $\mathbb{R}^{d}\times\mathbb{R}$. In such a case, it is shown that when the real part of the symbol function of the spatial operator is inferiorly bounded by a strictly positive constant, there exists a unique solution whose both spatial and spatio-temporal Fourier transforms are slow-growing measures over $\mathbb{R}^{d}\times\mathbb{R}$, and which also has a c\`adl\`ag-in-time behaviour. In addition, it is proven that the solution to an associated Cauchy problem converges spatio-temporally asymptotically to this unique solution as the time flows long enough.