Small values of Weyl sums

We prove that the set of $(x_1, \ldots, x_d)\in [0,1)^d$, such that $$\underline{\lim}_{N\to \infty}\left| \sum_{n=1}^N\exp(2 \pi i (x_1n+\ldots + x_dn^d)) \right| =0,$$ contains a dense $\mathcal{G}_\delta$ set in $[0,1)^d$ and has a positive Hausdorff dimension. Similar statements are also established for the generalised Gaussian sums $$\sum_{n=1}^N\exp(2\pi i x n^d), \qquad x \in [0,1).$$