0
$\begingroup$

I would like to know what the current best estimation for the upper bound of the exponential sum $$\left|\sum_{n=1}^N \exp \left(2 \pi i\alpha\left(x_0+x_1 n+\ldots+x_d n^d\right)\right)\right|=\left|\sum_{n=1}^N e(P(n)\alpha)\right|$$ that only require $\alpha$ to be an irrational number and fix a given $d\geq 2$ and a polynomial with integer coefficients $P(n)=x_0+x_1 n+\ldots+x_d n^d$, where $x_i\in \mathbb{N}$ and $x_d\neq0$, and I have not found any particularly good references.

From the work of Weyl and Van der Corput, we know

$\left|\sum_{n=1}^N e(P(n)\alpha)\right| \lesssim_{d, \epsilon, \alpha} N^{1+\epsilon}\left(q^{-1}+N^{-1}+q N^{-d}\right)^\frac{1}{2^d}$

From the work of Vinogrodov, we know

$\left|\sum_{n=1}^N e(P(n)\alpha)\right| \lesssim_{d, \epsilon, \alpha} N^{1+\epsilon}\left(q^{-1}+N^{-1}+q N^{-d}\right)^\frac{1}{C d^2 \log d}$

From the work of Decoupling (J Bourgain, C Demeter, L Guth), we know

$\left|\sum_{n=1}^N e(P(n)\alpha)\right| \lesssim_{d, \epsilon, \alpha} N^{1+\epsilon}\left(q^{-1}+N^{-1}+q N^{-d}\right)^\frac{1}{d(d-1)}$

Thank you in advance.

$\endgroup$
3
  • $\begingroup$ If we drop the case of endpoints, this is equivalent to how bad the uniformity of the distribution of the values of a polynomial in a finite field of characteristic p becomes as p tends to infinity. $\endgroup$
    – katago
    Commented Dec 21, 2023 at 18:36
  • 2
    $\begingroup$ What does it mean for a number to be "diophantine"? $\endgroup$ Commented Dec 22, 2023 at 19:29
  • 1
    $\begingroup$ @Gerry Myerson Thank you for pointing it out, I apologize for not expressing it clearly. It refers to irrational numbers that satisfy the Diophantine condition. What I mean is that the last term of the continued fraction expansion of α can be well controlled by the previous terms. I think the Diophantine condition should be a slightly weaker control than the boundedness of the term of the continued fraction. $\endgroup$
    – katago
    Commented Dec 22, 2023 at 21:22

0

You must log in to answer this question.

Browse other questions tagged .