Decay estimates for massive Dirac equation in a constant magnetic field

Abstract

We study the deacy and Strichartz estimates for the massive Dirac Hamiltonian in a constant magnetic fields in $\mathbb{R}_t\times\mathbb{R}^2_x$: \begin{equation*} \begin{cases} i\partial_tu(t,x)-\mathcal{D}_Au(t,x)=0, u(0,x)=f, \end{cases} \end{equation*} where $\mathcal{D}_A=-i{\bf \sigma}\cdot (\nabla-i{\bf A}(x))+\sigma_3m$ with $m\geq0$ being the mass and $\sigma_i$ being the Dirac matrices and the potential ${\bf A}(x)=\frac{B_0}{2}(-x_2,x_1),\,B_0>0$. In particular, we show the $L^1(\mathbb{R}^2)\to L^\infty(\mathbb{R}^2)$ type micro-localized decay estimates, for any finite time $T>0$, there exists a constant $C_T$ such that \begin{equation*} \|e^{it\mathcal{D}_{A}}\varphi(2^{-j}|\mathcal{D}_{A}|)f(x)\|_{[L^{\infty}(\mathbb{R}^2)]^2} \leq C_T 2^{2j}(1+2^{j}|t|)^{-\frac12} \|\varphi(2^{-j}|\mathcal{D}_{A}|)f\|_{[L^1{(\mathbb{R}^2)]^2}}, \quad |t|\leq T, \end{equation*} and we further prove the local-in-time Strichartz estimates for the Dirac equations with this unbounded potential.