The character sum cancellation conjecture for rough integers

Let qq be large and let χ\chi be a non-principal character modulo qq. For real numbers xx and yy satisfying

logqyx,\log q\leq y\leq x,

and writing P(n)P(n) for the largest prime factor of nn and e(α)=e2πiαe(\alpha)=e^{2\pi i\alpha}, the rough character sum conjecture.

maxα[0,1]nx(n)>yχ(n)ne(αn)1.\max_{\alpha\in[0,1]}\left|\sum_{\substack{n\leq x\P(n)>y}}\frac{\chi(n)}{n}e(\alpha n)\right|\ll 1.

If true, this would make the inequalities in the paper's main lower bounds equalities, supporting the claim that those results are best possible; the source gives no resolution of the conjecture.

Sources & referencesView supporting material

Primary source

Crystel Bujold, “Long large character sums”, arXiv:2005.11386 (2020).

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