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Kazuhiro Ito

Publications and source records attributed to Kazuhiro Ito.

16 recordsLinked to original sources
arXiv2026

From Detection to Characterization: A Large-Scale Study of Ragebait on Japanese X

Ragebait refers to online content intentionally designed to provoke anger or outrage and thereby increase attention and engagement. However, reliable large-scale detection and systematic analysis of ragebait remain limited, hindering efforts to understand its prevalence, impact, and mitigation. This study aims to develop an effective ragebait detection framework and to clarify the characteristics of ragebait at scale, providing a basis for understanding and mitigating emotionally provocative content online. We constructed a labeled dataset with the assistance of a large language model (LLM) and trained several Japanese language models for ragebait detection. The resulting ensemble classifier was then applied to a large-scale dataset of Japanese-language posts on X. Our analysis shows that ragebait is more prevalent in politically and socially contentious topics, including politics, discrimination, public health, and interpersonal conflict. Ragebait posts also spread faster and receive more negative reactions than non-ragebait posts, particularly anger, fear, disgust, sadness, and surprise. These findings demonstrate the utility of the proposed detector and provide a large-scale characterization of ragebait in Japanese online discourse.

cs.SI↗
arXiv2026

Close fields, affine Springer fibers and fundamental lemmas

We prove a geometric local constancy theorem for affine Springer fibers in families of close local fields. Consequently, stable orbital integrals are locally constant in these families, and both the base change fundamental lemma and the standard endoscopic fundamental lemma transfer from characteristic zero to arbitrary positive characteristic.

math.NT↗
arXiv2025

Arithmetic monodromy of hyper-Kähler varieties over $p$-adic fields

In this paper, we study the $p$-adic and $\ell$-adic monodromy operators associated with hyper-Kähler varieties over $p$-adic fields, in connection with Looijenga-Lunts-Verbitsky Lie algebras. We investigate a conjectural relation between the nilpotency indices of these monodromy operators on higher-degree cohomology groups and on the second cohomology, which may be viewed as an arithmetic analogue of Nagai's conjecture for degenerations of hyper-Kähler manifolds over a disk. We verify this arithmetic version of Nagai's conjecture for hyper-Kähler varieties over $p$-adic fields, assuming they belong to one of the four known deformation types. As part of our approach, we introduce a new method to analyze the $p$-adic cohomology of hyper-Kähler varieties via Sen's theory.

math.AG↗
arXiv2025

Deformation theory for prismatic $G$-displays

For a smooth affine group scheme $G$ over the ring of $p$-adic integers and a cocharacter $μ$ of $G$, we develop the deformation theory for $G$-$μ$-displays over the prismatic site of Bhatt-Scholze, and discuss how our deformation theory can be interpreted in terms of prismatic $F$-gauges introduced by Drinfeld and Bhatt-Lurie. As an application, we prove the local representability and the formal smoothness of integral local Shimura varieties with hyperspecial level structure. We also revisit and extend some classification results of $p$-divisible groups.

math.NT↗
arXiv2024

Vanishing of Brauer groups of moduli stacks of stable curves

We show that the cohomological Brauer groups of the moduli stacks of stable genus $g$ curves over the integers and an algebraic closure of the rational numbers vanish for any $g\geq 2$. For the $n$ marked version, we show the same vanishing result in the range $(g,n)=(1,n)$ with $1\leq n \leq 6$ and all $(g,n)$ with $g\geq 4.$ We also discuss several finiteness results on cohomological Brauer groups of proper and smooth Deligne-Mumford stacks over the integers.

math.AG↗
arXiv2024

Prismatic $G$-displays and descent theory

For a smooth affine group scheme $G$ over the ring of $p$-adic integers $\mathbb{Z}_p$ and a cocharacter $μ$ of $G$, we study $G$-$μ$-displays over the prismatic site of Bhatt-Scholze. In particular, we obtain several descent results for them. If $G=\mathrm{GL}_n$, then our $G$-$μ$-displays can be thought of as Breuil-Kisin modules with some additional conditions. The relation between our $G$-$μ$-displays and prismatic $F$-gauges introduced by Drinfeld and Bhatt-Lurie is also discussed. In fact, our results are formulated and proved for smooth affine group schemes over the ring of integers $\mathcal{O}_E$ of any finite extension $E$ of $\mathbb{Q}_p$ by using $\mathcal{O}_E$-prisms, which are $\mathcal{O}_E$-analogues of prisms.

math.AG↗
arXiv2022

The Hodge standard conjecture for self-products of K3 surfaces

As an application of our previous work on CM liftings of K3 surfaces and the Tate conjecture, we prove the Hodge standard conjecture for squares of K3 surfaces. We also deduce the Hodge standard conjecture for all the powers of certain K3 surfaces.

math.AG↗
arXiv2020

Uniform local constancy of étale cohomology of rigid analytic varieties

We prove some $\ell$-independence results on local constancy of étale cohomology of rigid analytic varieties. As a result, we show that a closed subscheme of a proper scheme over an algebraically closed complete non-archimedean field has a small open neighborhood in the analytic topology such that, for every prime number $\ell$ different from the residue characteristic, the closed subscheme and the open neighborhood have the same étale cohomology with $\mathbb Z/\ell \mathbb Z$-coefficients. The existence of such an open neighborhood for each $\ell$ was proved by Huber. A key ingredient in the proof is a uniform refinement of a theorem of Orgogozo on the compatibility of the nearby cycles over general bases with base change.

math.AG↗
arXiv2020

On a torsion analogue of the weight-monodromy conjecture

We formulate and study a torsion analogue of the weight-monodromy conjecture for a proper smooth scheme over a non-archimedean local field. We prove it for proper smooth schemes over equal characteristic non-archimedean local fields, abelian varieties, surfaces, varieties uniformized by Drinfeld upper half spaces, and set-theoretic complete intersections in toric varieties. In the equal characteristic case, our methods rely on an ultraproduct variant of Weil II established by Cadoret.

math.NT↗
arXiv2020

Deformations of rational curves in positive characteristic

We study deformations of rational curves and their singularities in positive characteristic. We use this to prove that if a smooth and proper surface in positive characteristic $p$ is dominated by a family of rational curves such that one member has all $δ$-invariants (resp. Jacobian numbers) strictly less than $(p-1)/2$ (resp. $p$), then the surface has negative Kodaira dimension. We also prove similar, but weaker results hold for higher dimensional varieties. Moreover, we show by example that our result is in some sense optimal. On our way, we obtain a sufficient criterion in terms of Jacobian numbers for the normalization of a curve over an imperfect field to be smooth.

math.AG↗
arXiv2018

CM liftings of K3 surfaces over finite fields and their applications to the Tate conjecture

We give applications of integral canonical models of orthogonal Shimura varieties and the Kuga-Satake morphism to the arithmetic of K3 surfaces over finite fields. We prove every K3 surface of finite height over a finite field admits a characteristic 0 lifting whose generic fiber is a K3 surface with complex multiplication. Combined with the results of Mukai and Buskin, we prove the Tate conjecture for the square of a K3 surface over a finite field. To obtain these results, we construct an analogue of Kisin's algebraic group for a K3 surface of finite height, and construct characteristic 0 liftings of the K3 surface preserving the action of tori in the algebraic group. We obtain these results for K3 surfaces over finite fields of any characteristics, including those of characteristic 2 or 3.

math.NT↗
arXiv2018

On the supersingular reduction of K3 surfaces with complex multiplication

We study the good reduction modulo p of K3 surfaces with complex multiplication. If a K3 surface with complex multiplication has good reduction, we calculate the Picard number and the height of the formal Brauer group of the reduction. Moreover, if the reduction is supersingular, we calculate its Artin invariant under some assumptions. Our results generalize some results of Shimada for K3 surfaces with Picard number 20. Our methods rely on the main theorem of complex multiplication for K3 surfaces by Rizov, an explicit description of the Breuil-Kisin modules associated with Lubin-Tate characters due to Andreatta, Goren, Howard, and Madapusi Pera, and the integral comparison theorem recently established by Bhatt, Morrow, and Scholze.

math.AG↗
arXiv2018

Unconditional construction of K3 surfaces over finite fields with given L-function in large characteristic

We give an unconditional construction of K3 surfaces over finite fields with given L-function, up to finite extensions of the base fields, under some mild restrictions on the characteristic. Previously, such results were obtained by Taelman assuming semistable reduction. The main contribution of this paper is to make Taelman's proof unconditional. We use some results of Nikulin and Bayer-Fluckiger to construct an appropriate complex projective K3 surface with CM which admits an elliptic fibration with a section, or an ample line bundle of low degree. Then using Saito's construction of strictly semistable models and applying a slight refinement of Matsumoto's good reduction criterion for K3 surfaces, we obtain a desired K3 surface over a finite field.

math.NT↗
arXiv2018

Finiteness of Brauer groups of K3 surfaces in characteristic 2

For a K3 surface over a field of characteristic 2 which is finitely generated over its prime subfield, we prove that the cokernel of the natural map from the Brauer group of the base field to that of the K3 surface is finite modulo the 2-primary torsion subgroup. In characteristic different from 2, such results were previously proved by A. N. Skorobogatov and Y. G. Zarhin. We basically follow their methods with an extra care in the case of superspecial K3 surfaces using the recent results of W. Kim and K. Madapusi Pera on the Kuga-Satake construction and the Tate conjecture for K3 surfaces in characteristic 2.

math.NT↗
arXiv2017

Existence of supersingular reduction for families of K3 surfaces with large Picard number in positive characteristic

We study non-isotrivial families of $K3$ surfaces in positive characteristic $p$ whose geometric generic fibers satisfy $ρ\geq21-2h$ and $h\geq3$, where $ρ$ is the Picard number and $h$ is the height of the formal Brauer group. We show that, under a mild assumption on the characteristic of the base field, they have potential supersingular reduction. Our methods rely on Maulik's results on moduli spaces of $K3$ surfaces and the construction of sections of powers of Hodge bundles due to van der Geer and Katsura. For large $p$ and each $2\leq{h}\leq10$, using deformation theory and Taelman's methods, we construct non-isotrivial families of $K3$ surfaces satisfying $ρ=22-2h$.

math.AG↗