Infinitely many solutions for doubly critical variable-order $p(x)$-Choquard-Kirchhoff type equations via the concentration compactness method

In this paper, we prove the existence of infinitely many solutions of a doubly critical Choquard-Kirchhoff type equation \begin{equation*} \begin{split} &M(\mathcal{E}[u])(-\Delta)_{p(\cdot,\cdot)}^{s(\cdot,\cdot)}u+V(x)|u|^{p(x)-2}u-\varepsilon_W W(x)|u|^{q_W(x)-2}u \\ &\quad\quad=\left(\int_{\mathbb{R}^N} \frac{|u(y)|^{r(y)}}{|x-y|^{\alpha(x,y)}}dy\right) |u|^{r(x)-2}u + |u|^{q_c(x)-2}u\quad\text{in $\mathbb{R}^N$} \end{split} \end{equation*} with variable smoothness. The exponents $r(\cdot)$ and $q_c(\cdot)$ are allowed to have critical growths at the same time in the sense of Hardy-Littlewood-Sobolev inequality and Sobolev inequality, respectively. In the course of consideration, we formulate a new Sobolev type embedding theorem for the Slobodeckij spaces with variable smoothness and extend the concentration compactness lemma to the variable exponent case in the form involving some nonlocal quantities. To obtain a sequence of solutions, we use a critical point theorem based on Krasnoselskii's genus.