A generalization of the Furstenberg--Sárközy theorem over the Gaussian integers

We introduce the notion of intersective polynomials over the Gaussian integers, and prove that given any intersective polynomial $p(x)$ over the Gaussian integers, every subset $A$ of the Gaussian integers of positive upper density contains two distinct elements such that their difference is $p(z)$ for some Gaussian integer $z$. Moreover, we also obtain a quantitative version of this result. The proof is motivated by an argument due to Lucier, and the Fourier-free proof of the Furstenberg--Sárközy theorem over the integers by Green, Tao and Ziegler.