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We introduce a $\mathbb{C}/\mathbb{Z}$-valued invariant of a foliated manifold with a stable framing and with a partially flat vector bundle. This invariant can be expressed in terms of integration in differential $K$-theory, or…

K-Theory and Homology · Mathematics 2018-06-25 Ulrich Bunke

Generalizing Fujita-Odaka invariant, we define a function $\tilde{\delta}$ on a set of generalized $b$-divisors over a smooth Fano variety. This allows us to provide a new characterization of uniform $K$-stability. A key role is played by a…

Algebraic Geometry · Mathematics 2023-04-27 Antonio Trusiani

We define the relative stability threshold of a family of Fano varieties over a DVR and show that it is computed by a divisorial valuation. In the case when the special fiber is K-unstable, but the generic fiber is K-semistable, we use the…

Algebraic Geometry · Mathematics 2025-10-08 Harold Blum , Yuchen Liu , Chenyang Xu , Ziquan Zhuang

We establish an algebraic approach to prove the properness of moduli spaces of K-polystable Fano varieties and reduce the problem to a conjecture on destabilizations of K-unstable Fano varieties. Specifically, we prove that if the stability…

Algebraic Geometry · Mathematics 2021-07-20 Harold Blum , Daniel Halpern-Leistner , Yuchen Liu , Chenyang Xu

We show that uniform K-stability is a Zariski open condition in Q-Gorenstein families of Q-Fano varieties. To prove this result, we consider the behavior of the stability threshold in families. The stability threshold (also known as the…

Algebraic Geometry · Mathematics 2020-06-11 Harold Blum , Yuchen Liu

It's well-known that adding a general boundary would create K-stability. As an application, we reprove product theorem for delta invariants of Fano varieties.

Algebraic Geometry · Mathematics 2025-01-06 Chuyu Zhou

We give a survey of the recent progress on the study of K-stability of Fano varieties by an algebro-geometric approach.

Algebraic Geometry · Mathematics 2020-11-23 Chenyang Xu

Using log canonical thresholds and basis divisors Fujita--Odaka introduced purely algebro-geometric invariants $\delta_m$ whose limit in $m$ is now known to characterize uniform K-stability on a Fano variety. As shown by Blum-Jonsson this…

Differential Geometry · Mathematics 2024-11-20 Yanir A. Rubinstein , Gang Tian , Kewei Zhang

We prove various results involving arcs - which generalise test configurations - within the theory of K-stability. Our main result characterises coercivity of the Mabuchi functional on spaces of Fubini-Study metrics in terms of uniform…

Algebraic Geometry · Mathematics 2024-09-23 Ruadhaí Dervan , Rémi Reboulet

We prove a criterion for K-stability of a $\mathbb{Q}$-Fano spherical variety with respect to equivariant special test configurations, in terms of its moment polytope and some combinatorial data associated to the open orbit. Combined with…

Algebraic Geometry · Mathematics 2020-09-16 Thibaut Delcroix

We consider the following generalization of the seminal Erd\H{o}s-Ko-Rado theorem, due to Frankl. For some k>=2, let F be a k-wise intersecting family of r-subsets of an n element set X, i.e. for any k sets F1,...,Fk in F, their…

Combinatorics · Mathematics 2013-04-03 Vikram Kamat

We prove that the stability condition for Fano manifolds defined by Saito-Takahashi, given in terms of the sum of the Ding invariant and the Chow weight, is equivalent to the existence of anticanonically balanced metrics. Combined with the…

Differential Geometry · Mathematics 2024-01-18 Yoshinori Hashimoto

We show that fixed dimensional klt weak Fano pairs with alpha-invariants and volumes bounded away from $0$ and the coefficients of the boundaries belong to the set of hyperstandard multiplicities $\Phi(\mathscr{R})$ associated to a fixed…

Algebraic Geometry · Mathematics 2018-10-24 Weichung Chen

We show that fixed dimensional klt weak Fano pairs with alpha-invariants and volumes bounded away from $0$ and the coefficients of the boundaries belonging to a fixed DCC set $S$ form a bounded family. Moreover, such pairs admit a strong…

Algebraic Geometry · Mathematics 2020-02-25 Weichung Chen

We extend the framework of K-stability (Tian, Donaldson) to more general algebro-geometric setting, such as partial desingularisations of (fixed) singularities, (not necessarily flat) families over higher dimensional base and the classical…

Algebraic Geometry · Mathematics 2014-11-21 Yuji Odaka

We show relationships between uniform K-stability and plt blowups of log Fano pairs. We see that it is enough to evaluate certain invariants defined by volume functions for all plt blowups in order to test uniform K-stability of log Fano…

Algebraic Geometry · Mathematics 2019-07-17 Kento Fujita

In this paper, we prove the openness of K-semistability in families of log Fano pairs by showing that the stability threshold is a constructible function on the fibers. We also prove that any special test configuration arises from a log…

Algebraic Geometry · Mathematics 2021-11-02 Harold Blum , Yuchen Liu , Chenyang Xu

We show that any $n$-dimensional Fano manifold $X$ with $\alpha(X)=n/(n+1)$ and $n\geq 2$ is K-stable, where $\alpha(X)$ is the alpha invariant of $X$ introduced by Tian. In particular, any such $X$ admits K\"ahler-Einstein metrics and the…

Algebraic Geometry · Mathematics 2016-06-28 Kento Fujita

We prove a product formula for $\delta$-invariant and as an application, we show that product of K-(semi, poly)stable Fano varieties is also K-(semi, poly)stable.

Algebraic Geometry · Mathematics 2021-02-22 Ziquan Zhuang

In this paper, we study the K-stability of polarized spherical varieties. After reduction, it can be treated as a variational problem of the reduced functional of the Futaki invariant on the associated moment polytope. With the convexity…

Differential Geometry · Mathematics 2022-01-17 Yan Li , Bin Zhou