Let $X$ be the degree $r$ Fermat hypersurface in $\mathbb{P}^{m-1}$. It is the critical locus of a regular function $W$ on the total space $Y$ of $\mathcal{O}(-r)$ over $\mathbb{P}^{m-1}$. Chang-Li developed a mathematical theory for the Landau-Ginzburg A-model on $(Y,W)$, known as stable maps with fields, and proved that it is equivalent to the Gromov-Witten theory of $X$. I will describe the theory of Mixed-Spin-P (MSP) fields which can be viewed as a mathematical theory of the Landau-Ginzburg A-model on $(M,W)$ where $M$ is the master space associated to $Y$. This is based on joint work with Huai-Liang Chang, Jun Li, and Wei-Ping Li.