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Sharp Transitions for Localized Solutions to a Diophantine Inequality

Number Theory · Submitted 18 Aug 2026 · 26 references

Pith's verdict: A genuinely new sharp existence threshold for non-integer-exponent Diophantine inequalities, with a major-arc uniformity gap that is fixable and a few small technical errors.

T0 · AI review

How this review was made: An AI referee (deepseek-v4-flash) read the paper on August 27, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID2608.18350 (version 1)
Pith ID65KR7ROP, Pith's permanent record of this paper and its review
CitationAtaleshvara Bhargava. "Sharp Transitions for Localized Solutions to a Diophantine Inequality." arXiv:2608.18350 (2026). https://pith.science/paper/65KR7ROP
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Referee report
The paper

The paper claims

A single critical constant separates guaranteed solutions from arbitrarily long gaps in a fractional-power Diophantine inequality.

The reading

This paper studies how many ways a large real number $R$ can be approximated by a sum of $s$ powers $x_i^\theta$ with non-integer $\theta>2$, when every variable is forced into a narrow window $X-Y < x_i \leq X+Y$ around the diagonal $X=(R/s)^{1/\theta}$. With window width $Y=c\sqrt{X}$, it proves a critical constant $\omega=(\lfloor s/2\rfloor(\theta-1))^{-1/2}$: for $c>\omega$ and enough variables, every sufficiently large $R$ has such solutions and the count grows like $X^{1-\theta}Y^{s-1}$; for $c<\omega$, infinitely many $R$ have none. The threshold is sharp except at $c=\omega$, left open. This matters because existence of integer approximations becomes a yes/no question governed by a single constant, and the zero case contradicts the naive heuristic that solutions should appear as soon as the window has enough volume.

What carries the argument

The load-bearing object is the exponential sum $f(\alpha_1,\alpha_2)=\sum_{X-Y<x\leq X+Y} e((x-X)\alpha_1+\alpha_2(x^\theta-X^\theta-\theta(x-X)X^{\theta-1}))$, whose $s$-th power is integrated against a smoothing kernel $K_\pm(\alpha_2)$ that converts the inequality $|\sum x_i^\theta-R|<\tau$ into a count. On the major arcs, $f$ is replaced by an integral approximation $f^*$, and the count is reduced to a two-dimensional integral $J_0(R,m)$ whose positivity is proved by finding a non-singular real solution $(\eta_1,\dots,\eta_s)$ to the system $\sum \gamma_i=m/Y$ and $\sum G(Y\gamma_i)=Z$, where $G(t)=(X+t)^\theta-X^\theta-\theta tX^{\theta-1}$. The sign of the quadratic form $\sum \gamma_i^2$, evaluated at two constructed points, changes exactly when $c$ crosses $\omega$, producing the transition. The minor and trivial arc bounds come from mean value estimates for exponential sums and a derivative test for exponential sums.

Extended reading notes

Core claim

The central claim is Theorems 1 and 2: the inequality family has a sharp transition at $\omega$. If $c>\omega$ and $s \geq (\lfloor 2\theta\rfloor+1)(\lfloor 2\theta\rfloor+2)+1$, then for all sufficiently large $R$ one has $N^\tau_{s,\theta}(R,c\sqrt{X}) \gg_{\theta,s} \tau X^{1-\theta}Y^{s-1}$. If $c<\omega$, a construction with $R=sM^\theta+s\theta M^{\theta-1}$ produces infinitely many $R_n\to\infty$ with $N^\tau_{s,\theta}(R_n,c\sqrt{X_n})=0$. The constant $\omega$ emerges from the balance between a linear and a quadratic term in the Taylor expansion of $(X+y)^\theta$ around $X$; this balance is the same mechanism that makes the major-arc integral change sign.

Load-bearing premise

The proof that the major-arc integral $J_0(R,m)$ is bounded below by a positive constant assumes that a standard truncation argument, taken from Lemmas 3.6.4 through 3.6.7 of [14], applies uniformly in $X$ and that the Jacobian determinant at the constructed solution is bounded away from zero; the paper proves existence and non-singularity but does not explicitly verify that uniform lower bound.

Editorial extensions

If this is right

  • The optimal window width for guaranteed existence is $Y \asymp \sqrt{X}$ up to a constant factor; any smaller constant in front of $\sqrt{X}$ produces arbitrarily large gaps.
  • For $c>\omega$, the lower bound $N \gg X^{1-\theta}Y^{s-1}$ has the order of magnitude one expects from the circle method, so the count is not merely positive but grows polynomially.
  • Theorem 2 requires only $s\geq 2$, so the obstruction for small $c$ is a geometric mismatch, not a shortage of variables.
  • The equality case $c=\omega$ is not settled; the paper suggests the behavior may depend on an additional power $X^\delta$ beyond $\sqrt{X}$.
  • The same dichotomy is likely to hold for the integer-power analogue, with the same mechanism but a different critical constant.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • One testable extension: for $c<\omega$, measure the density of the exceptional set of $R$ with no solutions; the construction here only shows the set is infinite, but it may well have positive density.
  • For intermediate numbers of variables, $\theta < s \leq 2\theta-1$, the exponent $X^{1-\theta}Y^{s-1}$ becomes negative, so if solutions exist the correct width may be $X^\kappa$ with $\kappa>1/2$ depending on $s$; this regime is out of reach of the present method.
  • Allowing the tolerance $\tau$ to grow with $R$ could reduce the required number of variables or the window constant, mirroring what happens in shifted sum-of-powers problems.
  • The sharpness at $\omega$ suggests a genuine phase transition; numerical searches near $c=\omega$ for specific $\theta$ and $s$ could reveal whether the transition is abrupt or accompanied by sparse sporadic solutions.
Original abstract

For fixed $\tau > 0$, non-integer $\theta > 2$ and large enough $s$, we investigate the number of solutions to the Diophantine inequality $|x_1^{\theta}+\cdots +x_s^{\theta} - R| < \tau$ as $R \to \infty$. Here, we restrict the variables $x_i$ in the ``almost diagonal" range $X-Y < x_i \leq X+Y$ for $i = 1, \ldots, s$, where $X = (R/s)^{1/\theta}$ and $Y \asymp \sqrt{X}$. Let $\omega = (\lfloor s/2 \rfloor(\theta-1))^{-1/2}$. We will show that if $Y = c\sqrt{X}$ for some $c > \omega$ then for sufficiently large $R$ there must always exist solutions, but if $c < \omega$ then there exist arbitrarily large positive $R$ for which there are no solutions. Our result is thus essentially sharp, with the exception of $c = \omega$. This work is analogous to the results of Daemen and Wright in which similar statements are proved for Waring's problem, though our results are likely somewhat stronger than what is possible in that setting. We discuss other related results and further work to be done.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,839 input tokens.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.93 · human participants 0.01 · controlled comparison 0.03 · randomized assignment 0.01 · states quantitative result 0.92 · compares with prior results 0.96 · mentions code or data availability 0.01.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

For fixed $\tau > 0$, non-integer $\theta > 2$ and large enough $s$, we investigate the number of solutions to the Diophantine inequality $|x_1^{\theta}+\cdots +x_s^{\theta} - R| < \tau$ as $R \to \infty$. Here, we restrict the variables $x_i$ in the ``almost diagonal" range $X-Y < x_i \leq X+Y$ for $i = 1, \ldots, s$, where $X = (R/s)^{1/\theta}$ and $Y \asymp \sqrt{X}$. Let $\omega = (\lfloor s/2 \rfloor(\theta-1))^{-1/2}$. We will show that if $Y = c\sqrt{X}$ for some $c > \omega$ then for sufficiently large $R$ there must always exist solutions, but if $c < \omega$ then there exist arbitrarily large positive $R$ for which there are no solutions. Our result is thus essentially sharp, with the exception of $c = \omega$. This work is analogous to the results of Daemen and Wright in which similar statements are proved for Waring's problem, though our results are likely somewhat stronger than what is possible in that setting. We discuss other related results and further work to be done.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 For fixed $\tau > 0$, non-integer $\theta > 2$ and large enough $s$, we investigate the number of solutions to the Diophantine inequality $|x_1^{\theta}+\cdots +x_s^{\theta} - R| < \tau$ as $R \to \infty$. contribution 0.67 0.73 0.03 unclear 0.56
s1 Here, we restrict the variables $x_i$ in the ``almost diagonal" range $X-Y < x_i \leq X+Y$ for $i = 1, \ldots, s$, where $X = (R/s)^{1/\theta}$ and $Y \asymp \sqrt{X}$. method 0.73 0.76 0.02 asserted 0.92
s2 Let $\omega = (\lfloor s/2 \rfloor(\theta-1))^{-1/2}$. method 0.55 0.48 0.02 asserted 0.58
s3 We will show that if $Y = c\sqrt{X}$ for some $c > \omega$ then for sufficiently large $R$ there must always exist solutions, but if $c < \omega$ then there exist arbitrarily large positive $R$ for which there are no solutions. result 1.00 0.93 0.93 asserted 1.00
s4 Our result is thus essentially sharp, with the exception of $c = \omega$. interpretation 0.75 0.89 0.27 asserted 0.96
s5 This work is analogous to the results of Daemen and Wright in which similar statements are proved for Waring's problem, though our results are likely somewhat stronger than what is possible in that setting. background 0.65 0.17 0.03 hedged possibility 0.88
s6 We discuss other related results and further work to be done. future work 1.00 0.19 0.01 unclear 0.58

What kind of paper the classifier reports this is: theoretical result 1.00 · evidence from proof or derivation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

References

Discussion

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