arXiv subjects

Yoshinosuke Hirakawa

Publications and source records attributed to Yoshinosuke Hirakawa.

12 recordsLinked to original sources

arXiv2025

A note on the second supplementary law of rational power residue symbols

As a natural generalization of the Legendre symbol, the $q$-th power residue symbol $(a/p)_q$ is defined for primes $p$ and $q$ with $p\equiv 1 \bmod q$. In this paper, we generalize the second supplementary law by providing an explicit condition for $(q/p)_q = 1$, when $p$ has a special form $p = \sum_{i=0}^{q-1} m^i n^{q-1-i}$. This condition is expressed in terms of the polylogarithm $\mathrm{Li}_{1-q}(x)$ of negative index. Our proof relies on an argument similar to Lemmermeyer's proof of Euler's conjectures for cubic residue.

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arXiv2024

Absolute zeta functions arising from ceiling and floor Puiseux polynomials

For the $\mathbb{Z}$-lift $X_\mathbb{Z}$ of a monoid scheme $X$ of finite type, Deitmar-Koyama-Kurokawa calculated its absolute zeta function by interpolating $\#X_\mathbb{Z}(\mathbb{F}_q)$ for all prime powers $q$ using the Fourier expansion. This absolute zeta function coincides with the absolute zeta function of a certain polynomial. In this article, we characterize the polynomial as a ceiling polynomial of the sequence $\left(\#X_\mathbb{Z}(\mathbb{F}_q)\right)_q$, which we introduce independently. Extending this idea, we introduce a certain pair of absolute zeta functions of a separated scheme $X$ of finite type over $\mathbb{Q}$ by means of a pair of Puiseux polynomials which estimate "$\#X(\mathbb{F}_{p^m})$" for sufficiently large $p$. We call them the ceiling and floor Puiseux polynomials of $X$. In particular, if $X$ is an elliptic curve, then our absolute zeta functions of $X$ do not depend on its isogeny class.

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arXiv2024

Quadratic fields, Artin-Schreier extensions, and Bell numbers

In this article, we prove a modulo $p$ congruence which connects the class number of the quadratic field $\mathbb{Q}(\sqrt{(-1)^{(p-1)/2}p})$ and the trace of a certain monomial in a root $θ$ of the Artin-Schreier polynomial $θ^{p}-θ-1$ over the field $\mathbb{F}_{p}$ of $p$ elements. This formula has a flavor of Dirichlet's class number formula which connects the class number and the $L$-value. The proof of our formula is based on several formulae satisfied by the Bell number, where the latter is defined as the number of partitions of $\{ 1, 2, ..., n \}$ and a purely combinatorial object. Among such formulae, we prove a generalization of the so called ``trace formula'' due to Barsky and Benzaghou which describes the special values of the Bell polynomials modulo $p$ by the trace mentioned above.

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arXiv2023

A note on the Diophantine equation $2ln^{2} = 1+q+ \cdots +q^α$ and application to odd perfect numbers

Let $N$ be an odd perfect number. Then, Euler proved that there exist some integers $n, α$ and a prime $q$ such that $N = n^{2}q^α$, $q \nmid n$, and $q \equiv α\equiv 1 \bmod 4$. In this note, we prove that the ratio $\frac{σ(n^{2})}{q^α}$ is neither a square nor a square times a single prime unless $α= 1$. It is a direct consequence of a certain property of the Diophantine equation $2ln^{2} = 1+q+ \cdots +q^α$, where $l$ denotes one or a prime, whose proof is based on the prime ideal factorization in the quadratic orders $\mathbb{Z}[\sqrt{1-q}]$ and the primitive solutions of generalized Fermat equations $x^β+y^β = 2z^{2}$. We give also a slight generalization to odd multiply perfect numbers.

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arXiv2023

Galois trace forms of type $A_{n}, D_{n}, E_{n}$ for odd $n$

Let $p$ be an odd prime number and $ζ_{p} := \exp(2πi/p)$. Then, it is well-known that the $A_{p-1}$-root lattice can be realized as the (Hermitian) trace form of the $p$-th cyclotomic extension $\mathbb{Q}(ζ_{p})/\mathbb{Q}$ restricted to the fractional ideal generated by $(1-ζ_{p})^{-(p-3)/2}$. In this paper, in contrast with the case of the $A_{p-1}$-root lattice, we prove the following theorem: Let $n$ be an odd positive integer and $F/\mathbb{Q}$ be a Galois extension of degree $n$. Then, there exist no fractional ideals $Λ$ of $F$ such that the restricted trace form $(Λ, \mathrm{Tr}|_{Λ\times Λ})$ is of type $A_{n}, D_{n}, E_{n}$. The proof is done by the prime ideal factorization of fractional ideals of $F$ with care of certain 2-adic obstruction. Additionally, we prove that every cyclic cubic field contains infinitely many distinct sub $\mathbb{Z}$-lattices of type $A_{3}$ (i.e., normalized face centered cubic lattices) with normal $\mathbb{Z}$-bases. The latter fact is in contrast with another fact that among quadratic fields only $\mathbb{Q}(\sqrt{\pm3})$ contain sub $\mathbb{Z}$-lattices of type $A_{2}$.

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arXiv2022

Elliptic analogue of irregular prime numbers for the $p^{n}$-division fields of the curves $y^{2} = x^{3}-(s^{4}+t^{2})x$

A prime number $p$ is said to be irregular if it divides the class number of the $p$-th cyclotomic field $\mathbb{Q}(ζ_{p}) = \mathbb{Q}(\mathbb{G}_m[p])$. In this paper, we study its elliptic analogue for the division fields of an elliptic curve. More precisely, for a prime number $p \geq 5$ and a positive integer $n$, we study the $p$-divisibility of the class number of the $p^{n}$-division field $\mathbb{Q}(E[p^{n}])$ of an elliptic curve $E$ of the form $y^{2} = x^{3}-(s^{4}+t^{2})x$. In particular, we construct a certain infinite subfamily consisting of curves with novel properties that they are of Mordell-Weil rank 1 and the class numbers of their $p^{n}$-division fields are divisible by $p^{2n}$. Moreover, we can prove that these division fields are not isomorphic to each other. In our construction, we use recent results obtained by the first author.

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arXiv2021

Primes of the form $X^{3}+NY^{3}$ and a family of non-singular plane curves which violate the local-global principle

Let $n$ be an integer such that $n = 5$ or $n \geq 7$. In this article, we introduce a recipe for a certain infinite family of non-singular plane curves of degree $n$ which violate the local-global principle. Moreover, each family contains infinitely many members which are not geometrically isomorphic to each other. Our construction is based on two arithmetic objects; that is, prime numbers of the form $X^{3}+NY^{3}$ due to Heath-Brown and Moroz and the Fermat type equation of the form $x^{3}+Ny^{3} = Lz^{n}$, where $N$ and $L$ are suitably chosen integers. In this sense, our construction is an extension of the family of odd degree $n$ which was previously found by Shimizu and the author. The previous construction works only if the given degree $n$ has a prime divisor which satisfies a certain indivisibility conjecture of Ankeny-Artin-Chowla-Mordell type. In this time, we focus on the complementary cases, namely the cases of even degrees and exceptional odd degrees. Consequently, our recipe works well as a whole. This means that we can unconditionally obtain infinitely many non-singular plane curves of every degree $n = 5$ or $n \geq 7$ which violate the local-global principle. This gives a conclusion of the classical story of searching explicit ternary forms violating the local-global principle, which was originated by Selmer (1951) and extended by Fujiwara (1972) and others.

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arXiv2020

Counterexamples to the local-global principle for non-singular plane curves and a cubic analogue of Ankeny-Artin-Chowla-Mordell conjecture

In this article, we introduce a systematic and uniform construction of non-singular plane curves of odd degrees $n \geq 5$ which violate the local-global principle. Our construction works unconditionally for $n$ divisible by $p^2$ for some odd prime number $p$. Moreover, our construction also works for $n$ divisible by some $p \geq 5$ which satisfies a conjecture on $p$-adic properties of the fundamental units of $\mathbb{Q}(p^{1/3})$ and $\mathbb{Q}((2p)^{1/3})$. This conjecture is a natural cubic analogue of the classical Ankeny-Artin-Chowla-Mordell conjecture for $\mathbb{Q}(p^{1/2})$ and easily verified numerically.

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arXiv2020

How to calculate the proportion of everywhere locally soluble diagonal hypersurfaces

In this paper, we establish a strategy for the calculation of the proportion of everywhere locally soluble diagonal hypersurfaces of $\mathbb{P}^{n}$ of fixed degree. Our strategy is based on the product formula established by Bright, Browning and Loughran. Their formula reduces the problem into the calculation of the proportions of $\mathbb{Q}_{v}$-soluble diagonal hypersurfaces for all places $v$. As worked examples, we carry out our strategy in the cases of quadratic and cubic hypersurfaces. As a consequence, we prove that around $99.99\%$ of diagonal cubic $4$-folds have $\mathbb{Q}$-rational points under a hypothesis on the Brauer-Manin obstruction.

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arXiv2019

Counterexamples to the local-global principle associated with Swinnerton-Dyer's cubic form

In this paper, we imitate a classical construction of a counterexample to the local-global principle of cubic forms of 4 variables which was discovered first by Swinnerton-Dyer (Mathematica (1962)). Our construction gives new explicit families of counterexamples in homogeneous forms of $4, 5, 6, ..., 2n+2$ variables of degree $2n+1$ for infinitely many integers $n$. It is contrastive to Swinnerton-Dyer's original construction that we do not need any concrete calculation in the proof of local solubility.

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arXiv2019

Infinitely many hyperelliptic curves with exactly two rational points

In this paper, we construct some families of infinitely many hyperelliptic curves of genus $2$ with exactly two rational points. In the proof, we first show that the Mordell-Weil ranks of these hyperelliptic curves are $0$ and then determine the sets of rational points by using the Lutz-Nagell type theorem for hyperelliptic curves which was proven by Grant.

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arXiv2018

A unique pair of triangles

A rational triangle is a triangle with sides of rational lengths. In this short note, we prove that there exists a unique pair of a rational right triangle and a rational isosceles triangle which have the same perimeter and the same area. In the proof, we determine the set of rational points on a certain hyperelliptic curve by a standard but sophisticated argument which is based on the 2-descent on its Jacobian variety and Coleman's theory of $p$-adic abelian integrals.

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