Fractional magnetic Schr\"{o}dinger-Kirchhoff problems with convolution and critical nonlinearities

In this paper we are concerned with the existence and multiplicity of solutions for the fractional Choquard-type Schr\"{o}dinger-Kirchhoff equations with electromagnetic fields and critical nonlinearity: \begin{eqnarray*} \begin{cases} \varepsilon^{2s}M([u]_{s,A}^2)(-\Delta)_{A}^su + V(x)u = (|x|^{-\alpha}*F(|u|^2))f(|u|^2)u + |u|^{2_s^\ast-2}u,\ \ \ x\in \mathbb{R}^N,\\ u(x) \rightarrow 0,\ \ \quad \mbox{as}\ |x| \rightarrow \infty, \end{cases} \end{eqnarray*} where $(-\Delta)_{A}^s$ is the fractional magnetic operator with $0<s<1$, $2_s^\ast = 2N/(N-2s)$, $\alpha < \min\{N, 4s\}$, $M : \mathbb{R}^{+}_{0}\rightarrow \mathbb{R}^{+}_0$ is a continuous function, $A: \mathbb{R}^N \rightarrow \mathbb{R}^N$ is the magnetic potential, $F(|u|) = \int_0^{|u|}f(t)dt$, and $\varepsilon > 0$ is a positive parameter. The electric potential $V\in C(\mathbb{R}^N, \mathbb{R}^+_0)$ satisfies $V(x) = 0$ in some region of $\mathbb{R}^N$, which means that this is the critical frequency case. We first prove the $(PS)_c$ condition, by using the fractional version of the concentration compactness principle. Then, applying also the mountain pass theorem and the genus theory, we obtain the existence and multiplicity of semiclassical states for the above problem. The main feature of our problems is that the Kirchhoff term $M$ can vanish at zero.