Solution to the Boltzmann equation in velocity-weighted Chemin-Lerner type spaces

TL;DR

This paper establishes the existence and uniqueness of global solutions to the Boltzmann equation near Maxwellians in velocity-weighted Chemin-Lerner spaces, handling both hard and soft potentials with new analytical techniques.

Contribution

It introduces a novel function space framework for global well-posedness of the Boltzmann equation, especially addressing the soft potential case with velocity weights and Besov regularity.

Findings

Global-in-time mild solutions are proven to exist and be unique.

The new function space effectively treats soft potentials with velocity weights.

Time-decay properties are crucial for the analysis of solutions.

Abstract

In this paper we study the Boltzmann equation near global Maxwellians in the $d$-dimensional whole space. A unique global-in-time mild solution to the Cauchy problem of the equation is established in a Chemin-Lerner type space with respect to the phase variable $(x,v)$. Both hard and soft potentials with angular cutoff are considered. The new function space for global well-posedness is introduced to essentially treat the case of soft potentials, and the key point is that the velocity variable is taken in the weighted supremum norm, and the space variable is in the $s$-order Besov space with $s\geq d/2$ including the spatially critical regularity. The proof is based on the time-decay properties of solutions to the linearized equation together with the bootstrap argument. Particularly, the linear analysis in case of hard potentials is due to the semigroup theory, where the extra time-decay plays a role in coping with initial data in $L^2$ with respect to space variable. In case of soft potentials, for the time-decay of linear equations we borrow the results basing on the pure energy method and further extend them to those in $L^\infty$ framework through the technique of $L^2$--$L^\infty$ interplay. In contrast to hard potentials, $L^1$ integrability in $x$ of initial data is necessary for soft potentials in order to obtain global solutions to the nonlinear Cauchy problem.