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For a prime $p$ and integers $a,m$, $0<a,m<p$ define the (partial Kloosterman) sum $$ S_p(a,m) = \sum_{0<k<m} \exp\left(\frac{2\pi\mathrm{i}}{p}(x + a x^{-1})\right), $$ where $x^{-1}$ is the multiplicative inverse of $x$ modulo $p$. I know $\Im S_p(a,p)=0$ and that there is the Weil bound $$ |\Re S_p(a,p)| \leq 2\sqrt{p}. $$

Is there a similar bound on $\Im S_p(a,m)$ that holds for all $m=1,\ldots,p$? I imagine this question might have a known answer in the literature, but I couldn't find anything. Conjectured bounds would also be interesting to me.

A related question: is the Weil bound true for partial sums as well, i.e., is it true that $$\max_m |\Re S_p(a,m)|\leq 2\sqrt{p}? $$

If I pretend that $(x+a x^{-1})/p$ is uniformly distributed in $[0,1]$, then the distribution of real and imaginary parts of each term is the same, but all imaginary terms cancel. So intuitively only half as many imaginary terms contribute to $\max_m |\Im S_p(a,m)|$ as there are real terms that altogether contribute to make up $2\sqrt{p}$. So I would expect some bound of the form $$ \max_m |\Im S_p(a,m)| \leq 2\sqrt{p/2}, $$ but I am not really convinced this is right (for example: should it be $2\sqrt{p/2}$ because $p$ is halved or $\sqrt{p}$ because the number of terms is halved but $p$ is the same?).

For a prime $p$ and integers $a,m$, $0<a,m<p$ define the (partial Kloosterman) sum $$ S_p(a,m) = \sum_{0<k<m} \exp\left(\frac{2\pi\mathrm{i}}{p}(a x + x^{-1})\right), $$ where $x^{-1}$ is the multiplicative inverse of $x$ modulo $p$. I know $\Im S_p(a,p)=0$ and that there is the Weil bound $$ |\Re S_p(a,p)| \leq 2\sqrt{p}. $$

Is there a similar bound on $\Im S_p(a,m)$ that holds for all $m=1,\ldots,p$? I imagine this question might have a known answer in the literature, but I couldn't find anything. Conjectured bounds would also be interesting to me.

A related question: is the Weil bound true for partial sums as well, i.e., is it true that $$\max_m |\Re S_p(a,m)|\leq 2\sqrt{p}? $$

If I pretend that $(x+a x^{-1})/p$ is uniformly distributed in $[0,1]$, then the distribution of real and imaginary parts of each term is the same, but all imaginary terms cancel. So intuitively only half as many imaginary terms contribute to $\max_m |\Im S_p(a,m)|$ as there are real terms that altogether contribute to make up $2\sqrt{p}$. So I would expect some bound of the form $$ \max_m |\Im S_p(a,m)| \leq 2\sqrt{p/2}, $$ but I am not really convinced this is right (for example: should it be $2\sqrt{p/2}$ because $p$ is halved or $\sqrt{p}$ because the number of terms is halved but $p$ is the same?).

For a prime $p$ and integers $a,m$, $0<a,m<p$ define the (partial Kloosterman) sum $$ S_p(a,m) = \sum_{0<k<m} \exp\left(\frac{2\pi\mathrm{i}}{p}(x + a x^{-1})\right), $$ where $x^{-1}$ is the multiplicative inverse of $x$ modulo $p$. I know $\Im S_p(a,p)=0$ and that there is the Weil bound $$ |\Re S_p(a,p)| \leq 2\sqrt{p}. $$

Is there a similar bound on $\Im S_p(a,m)$ that holds for all $m=1,\ldots,p$? I imagine this question might have a known answer in the literature, but I couldn't find anything. Conjectured bounds would also be interesting to me.

If I pretend that $(x+a x^{-1})/p$ is uniformly distributed in $[0,1]$, then the distribution of real and imaginary parts of each term is the same, but all imaginary terms cancel. So intuitively only half as many imaginary terms contribute to $\max_m |\Im S_p(a,m)|$ as there are real terms that altogether contribute to make up $2\sqrt{p}$. So I would expect some bound of the form $$ \max_m |\Im S_p(a,m)| \leq 2\sqrt{p/2}, $$ but I am not really convinced this is right (for example: should it be $2\sqrt{p/2}$ because $p$ is halved or $\sqrt{p}$ because the number of terms is halved but $p$ is the same?).

For a prime $p$ and integers $a,m$, $0<a,m<p$ define the (partial Kloosterman) sum $$ S_p(a,m) = \sum_{0<k<m} \exp\left(\frac{2\pi\mathrm{i}}{p}(x + a x^{-1})\right), $$ where $x^{-1}$ is the multiplicative inverse of $x$ modulo $p$. I know $\Im S_p(a,p)=0$ and that there is the Weil bound $$ |\Re S_p(a,p)| \leq 2\sqrt{p}. $$

Is there a similar bound on $\Im S_p(a,m)$ that holds for all $m=1,\ldots,p$? I imagine this question might have a known answer in the literature, but I couldn't find anything. Conjectured bounds would also be interesting to me.

A related question: is the Weil bound true for partial sums as well, i.e., is it true that $$\max_m |\Re S_p(a,m)|\leq 2\sqrt{p}? $$

If I pretend that $(x+a x^{-1})/p$ is uniformly distributed in $[0,1]$, then the distribution of real and imaginary parts of each term is the same, but all imaginary terms cancel. So intuitively only half as many imaginary terms contribute to $\max_m |\Im S_p(a,m)|$ as there are real terms that altogether contribute to make up $2\sqrt{p}$. So I would expect some bound of the form $$ \max_m |\Im S_p(a,m)| \leq 2\sqrt{p/2}, $$ but I am not really convinced this is right (for example: should it be $2\sqrt{p/2}$ because $p$ is halved or $\sqrt{p}$ because the number of terms is halved but $p$ is the same?).

For a prime $p$ and integers $a,m$, $0<a,m<p$ define the (partial Kloosterman) sum $$ S_p(a,m) = \sum_{0<k<m} \exp\left(\frac{2\pi\mathrm{i}}{p}(x + a x^{-1})\right), $$ where $x^{-1}$ is the multiplicative inverse of $x$ modulo $p$. I know $\Im S_p(a,p)=0$ and that there is the Weil bound $$ |\Re S_p(a,p)| \leq 2\sqrt{p}. $$

Is there a similar bound on $\Im S_p(a,m)$ that holds for all $m=1,\ldots,p$? I imagine this question might have a known answer in the literature, but I couldn't find anything. Conjectured bounds would also be interesting to me.

If I pretend that $(x+a x^{-1})/p$ is uniformly distributed in $[0,1]$, then the distribution of real and imaginary parts of each term is the same, but all imaginary terms cancel. So intuitively only half as many imaginary terms contribute to $\max_m |\Im S_p(a,m)|$ as there are real terms that altogether contribute to make up $2\sqrt{p}$. So I would expect some bound of the form $$ \max_m |\Im S_p(a,m)| \leq 2\sqrt{p/2}, $$ but I am not really convinced this is right.

For a prime $p$ and integers $a,m$, $0<a,m<p$ define the (partial Kloosterman) sum $$ S_p(a,m) = \sum_{0<k<m} \exp\left(\frac{2\pi\mathrm{i}}{p}(x + a x^{-1})\right), $$ where $x^{-1}$ is the multiplicative inverse of $x$ modulo $p$. I know $\Im S_p(a,p)=0$ and that there is the Weil bound $$ |\Re S_p(a,p)| \leq 2\sqrt{p}. $$

Is there a similar bound on $\Im S_p(a,m)$ that holds for all $m=1,\ldots,p$? I imagine this question might have a known answer in the literature, but I couldn't find anything. Conjectured bounds would also be interesting to me.

If I pretend that $(x+a x^{-1})/p$ is uniformly distributed in $[0,1]$, then the distribution of real and imaginary parts of each term is the same, but all imaginary terms cancel. So intuitively only half as many imaginary terms contribute to $\max_m |\Im S_p(a,m)|$ as there are real terms that altogether contribute to make up $2\sqrt{p}$. So I would expect some bound of the form $$ \max_m |\Im S_p(a,m)| \leq 2\sqrt{p/2}, $$ but I am not really convinced this is right (for example: should it be $2\sqrt{p/2}$ because $p$ is halved or $\sqrt{p}$ because the number of terms is halved but $p$ is the same?).