Small ideals in polynomial rings and applications

Abstract

Let $\mathbf{k}$ be a field which is either finite or algebraically closed and let $R=\mathbf{k}[x_1,\dots ,x_n].$ We prove that any $g_1,\dots ,g_s\in R$ homogeneous of positive degrees $\le d$ are contained in an ideal generated by an $R_t$-sequence of $\le A(d)(s+t{)}^{B(d)}$ homogeneous polynomials of degree $\le d,$ subject to some restrictions on the characteristic of $\mathbf{k}.$ This yields effective bounds for new cases of Ananyan and Hochster's theorem A in arXiv:1610.09268 on strength and the codimension of the singular locus. It also implies effective bounds when $d$ equals the characteristic of $\mathbf{k}$ for Tao and Ziegler's result in arXiv:1101.1469 on rank and $U^d$ Gowers norms of polynomials over finite fields.