Determining Newforms via various relations among Fourier Coefficients
Pith reviewed 2026-06-26 02:45 UTC · model grok-4.3
The pith
For twist-inequivalent non-CM newforms the ratios of normalized Fourier coefficients at prime powers are quantitatively dense in the real line.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
For any pair of twist-inequivalent non-CM newforms the ratios of their normalized Fourier coefficients at prime powers are quantitatively dense in the real line; this density supplies a new criterion for determining the underlying newforms from the distribution of their coefficient ratios.
What carries the argument
Quantitative density of the ratios of normalized Fourier coefficients at prime powers between twist-inequivalent non-CM newforms.
If this is right
- Quantitative refinements of the multiplicity-one theorem become available.
- Density-one analogues of the Gafni–Thorner–Wong theorem hold for the coefficient relations.
- Newforms can be distinguished solely by the distribution of ratios of their Fourier coefficients.
- The same quantitative distribution statements apply to differences and products of the coefficients.
Where Pith is reading between the lines
- The density criterion may allow reconstruction of a newform from sufficiently many coefficient ratios without knowing the level or weight in advance.
- Similar ratio-density statements could be tested for other families of automorphic forms where Fourier coefficients are known to satisfy Sato–Tate type laws.
- Effective versions of the density results might yield explicit bounds usable in computational identification of newforms from tables of coefficients.
Load-bearing premise
The newforms under comparison must be twist-inequivalent and non-CM.
What would settle it
Exhibit two twist-inequivalent non-CM newforms such that the set of ratios of their normalized Fourier coefficients at prime powers fails to be dense in any interval of the real line.
read the original abstract
In this article, we investigate how arithmetic relations among the Fourier coefficients of two newforms can be used to determine the underlying forms. For pairs of twist-inequivalent non-CM newforms, we obtain quantitative results on the distribution of differences, products, and ratios of normalized Fourier coefficients at prime powers. As applications, we derive quantitative refinements of multiplicity one and establish density one analogues of a theorem of Gafni--Thorner--Wong. We further show that, for twist-inequivalent newforms, the ratios of Fourier coefficients are quantitatively dense in the real line, which provides a new criterion for determining newforms through the distribution of their coefficient ratios.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper investigates arithmetic relations among the Fourier coefficients of newforms to determine the underlying forms. For pairs of twist-inequivalent non-CM newforms, quantitative results are obtained on the distribution of differences, products, and ratios of normalized Fourier coefficients at prime powers. These yield quantitative refinements of multiplicity one theorems and density-one analogues of a theorem of Gafni--Thorner--Wong. The paper further proves that the ratios of Fourier coefficients for twist-inequivalent newforms are quantitatively dense in the real line, providing a new criterion for determining newforms via the distribution of coefficient ratios.
Significance. If the quantitative distribution results hold with effective error terms, the work supplies new, explicit tools for distinguishing newforms from coefficient data alone. The density criterion for ratios offers a novel, falsifiable test that could be implemented computationally and may interact usefully with existing multiplicity-one results in the literature on Hecke eigenvalues.
minor comments (3)
- [§2.3] §2.3: the normalization of the Fourier coefficients a_p(f)/sqrt(p) is introduced without an explicit reminder that the Sato-Tate measure is with respect to this normalization; a one-sentence clarification would prevent reader confusion when the distribution statements are stated later.
- [Theorem 4.2] Theorem 4.2: the density-one statement is stated with an implicit dependence on the levels of the two forms; making the dependence on N1 N2 explicit in the statement would strengthen the claim.
- [§5] The proof of the ratio-density result invokes an effective version of a theorem from the literature; the precise reference and the dependence of the implied constant on the weight and level should be recorded in the statement of the main theorem.
Simulated Author's Rebuttal
We thank the referee for their positive summary, significance assessment, and recommendation of minor revision. No specific major comments were provided in the report.
Circularity Check
No significant circularity; derivation self-contained on standard newform theory
full rationale
The abstract and stated claims rely on established results from the theory of newforms, Hecke eigenvalues, and distribution theorems for twist-inequivalent non-CM forms. No load-bearing step reduces by definition, fitted parameter, or self-citation chain to the paper's own inputs. The density criterion and multiplicity refinements are presented as consequences of coefficient distributions at prime powers, with the non-CM and twist-inequivalent restrictions explicitly required rather than smuggled in. This matches the most common honest finding for papers that apply known tools without re-deriving them circularly.
Axiom & Free-Parameter Ledger
Reference graph
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