Conjecture on polynomial exponential sums becoming kloostermanian functions

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For u,v∈Zu,v\in\mathbb{Z}, c∈Nc\in\mathbb{N}, and polynomials g,h∈Z[x]g,h\in\mathbb{Z}[x], define

A(ug,vh;c)=∑x (mod⁡c)e(ug(x)+vh(x)c),A(ug,vh;c)=\sum_{x \, (\operatorname{mod}{ c})}e\left(\frac{ug(x)+vh(x)}{c}\right),

and

A~(ug,vh;c)=∑x (mod⁡c)(xc)e(ug(x)+vh(x)c).\widetilde{A}(ug,vh;c)=\sum_{x \, (\operatorname{mod}{ c})}\left(\frac{x}{c}\right)e\left(\frac{ug(x)+vh(x)}{c}\right).

Also define the corresponding sums over invertible residue classes by

A×(ug,vh;c)=∑x(mod⁡c)\xx‾≡1,(mod⁡c)e(ug(x)+vh(x‾)c)A^{\times}(ug,vh;c)=\sum_{\substack{x \, (\operatorname{mod}{ c})\\\x\overline{x}\equiv1\\,(\operatorname{mod}{ c})}}e\left(\frac{ug(x)+vh(\overline{x})}{c}\right)

and

A~×(ug,vh;c)=∑x(mod⁡c)\xx‾≡1,(mod⁡c)(xc)e(ug(x)+vh(x‾)c).\widetilde{A}^{\times}(ug,vh;c)=\sum_{\substack{x \, (\operatorname{mod}{ c})\\\x\overline{x}\equiv1\\,(\operatorname{mod}{ c})}}\left(\frac{x}{c}\right)e\left(\frac{ug(x)+vh(\overline{x})}{c}\right).

Here the four sums are T-multiplicative arithmetic functions of cc.

Polynomial exponential-sum conjecture. If gg and hh satisfy

min⁡deg⁡(g),deg⁡(h)⩾1,max⁡deg⁡(g),deg⁡(h)⩾3,\min\\{\deg(g),\deg(h)\\}\geqslant1,\qquad \max\\{\deg(g),\deg(h)\\}\geqslant3,

then there exists an integer pair a,ba,b such that A(ag,bh;c)A(ag,bh;c) is a kloostermanian arithmetic function and A~(ag,bh;c)\widetilde{A}(ag,bh;c) is an almost-kloostermanian arithmetic function. If gg and hh satisfy min⁡deg⁡(g),deg⁡(h)⩾1\min\\{\deg(g),\deg(h)\\}\geqslant1, then there exists an integer pair a,ba,b such that A×(ag,bh;c)A^{\times}(ag,bh;c) is a kloostermanian arithmetic function and A~×(ag,bh;c)\widetilde{A}^{\times}(ag,bh;c) is an almost-kloostermanian arithmetic function.

These assertions propose that suitable integer rescalings of polynomial exponential sums, including their quadratic-character twists and invertible-variable variants, can exhibit the same arithmetic behavior as Kloosterman-type functions. The supplied text gives no resolution, so the conjecture remains open.

References

Primary source

Yang Zhang, “Distinction between hyper-Kloosterman sums and multiplicative functions”, arXiv:2510.10721 (2025).

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