Picard Lattice Research Articles

Mutations of numerically exceptional collections on surfaces

A conjecture of Bondal–Polishchuk states that, in particular for the bounded derived category of coherent sheaves on a smooth projective variety, the action of the braid group on full exceptional collections is transitive up to shifts. We show that the braid group acts transitively on the set of maximal numerically exceptional collections on rational surfaces up to isometries of the Picard lattice and twists with line bundles. Considering the blow-up of the projective plane in up to 9 points in very general position, these results lift to the derived category. More precisely, we prove that, under these assumptions, a maximal numerically exceptional collection consisting of line bundles is a full exceptional collection and any two of them are related by a sequence of mutations and shifts. The former extends a result of Elagin–Lunts and the latter a result of Kuleshov–Orlov, both concerning del Pezzo surfaces. In contrast, we show in concomitant work (Krah in Invent Math 235(3):1009–1018, 2024) that the blow-up of the projective plane in 10 points in general position admits a non-full exceptional collection of maximal length consisting of line bundles.

On the Galois-invariant part of the Weyl group of the Picard lattice of a K3 surface

Let X denote a K3 surface over an arbitrary field k. Let ks denote a separable closure of k and let Xs denote the base change of X to ks. Let O(PicX) and O(PicXs) denote the group of isometries of the lattices PicX and PicXs, respectively. Let RX denote the Galois invariant part of the Weyl group of PicXs. One can show that each element in RX can be restricted to an element of O(PicX). The following question arises: Is the image of the restriction mapRX→O(PicX)a normal subgroup of O(PicX)for every K3 surface X? We show that the answer is negative by giving counterexamples over k=Q.

A note on simple K3 singularities and families of weighted K3 surfaces

We discuss properties of the Seifert form for simple K3 singularities, and of the Picard lattices of families of weighted K3 surfaces. We study a collection $$\mathcal {M}_{(\rho ,\,\delta )}$$ of K3 surfaces polarized by their Picard lattices that are in the set $$\mathcal {L}_{(\rho ,\,\delta )}$$ of certain lattices. We also report a numerical formula that relates the Seifert form for the singularities and the Picard lattice of the family.

A Hilbert irreducibility theorem for Enriques surfaces

We define the over-exceptional lattice of a minimal algebraic surface of Kodaira dimension 0 0 . Bounding the rank of this object, we prove that a conjecture by Campana [Ann. Inst. Fourier (Grenoble) 54 (2004), pp. 499–630] and Corvaja–Zannier [Math. Z. 286 (2017), pp. 579–602] holds for Enriques surfaces, as well as K3 surfaces of Picard rank ≥ 6 \geq 6 apart from a finite list of geometric Picard lattices. Concretely, we prove that such surfaces over finitely generated fields of characteristic 0 0 satisfy the weak Hilbert Property after a finite field extension of the base field. The degree of the field extension can be uniformly bounded.

Classification of Degenerations of Codimension $${\le}\,5$$ and Their Picard Lattices for Kählerian K3 Surfaces with the Symplectic Automorphism Group $$(C_2)^2$$

Classification of Degenerations of Codimension $${\le}\,5$$ and Their Picard Lattices for Kählerian K3 Surfaces with the Symplectic Automorphism Group $$(C_2)^2$$

Classification of Degenerations of Codimension ${\le } 5$ and Their Picard Lattices for Kählerian K3 Surfaces with the Symplectic Automorphism Group $(C_2)^2$

В работах автора 2013-2018 гг. были классифицированы вырождения и решетки Пикара кэлеровых K3-поверхностей с конечными симплектическими группами автоморфизмов высокого порядка. Для оставшихся групп малого порядка $D_6$, $C_4$, $(C_2)^2$, $C_3$, $C_2$ и $C_1$ данная классификация полностью не рассматривалась, так как каждый из этих случаев требует очень долгих и трудных рассмотрений и вычислений. Случаи $D_6$ и $C_4$ были недавно полностью рассмотрены. Здесь рассматривается аналогичная полная классификация для группы $(C_2)^2$ порядка $4$. Исследуются ее вырождения коразмерности ${\le } 5$. Данная группа также имеет вырождения коразмерностей $6$ и $7$, классификация которых будет рассмотрена в последующих работах.

Deep Learning Gauss\u2013Manin Connections

The Gauss–Manin connection of a family of hypersurfaces governs the change of the period matrix along the family. This connection can be complicated even when the equations defining the family look simple. When this is the case, it is expensive to compute the period matrices of varieties in the family via homotopy continuation. We train neural networks that can quickly and reliably guess the complexity of the Gauss–Manin connection of pencils of hypersurfaces. As an application, we compute the periods of 96% of smooth quartic surfaces in projective 3-space whose defining equation is a sum of five monomials; from the periods of these quartic surfaces, we extract their Picard lattices and the endomorphism fields of their transcendental lattices.

Flops, Gromov-Witten invariants and symmetries of line bundle cohomology on Calabi-Yau three-folds

The zeroth line bundle cohomology on Calabi-Yau three-folds encodes information about the existence of flop transitions and the genus zero Gromov-Witten invariants. We illustrate this claim by studying several Picard number 2 Calabi-Yau three-folds realised as complete intersections in products of projective spaces. Many of these manifolds exhibit certain symmetries on the Picard lattice which preserve the zeroth cohomology.

Rational elliptic surfaces and the trigonometry of tetrahedra

We study the trigonometry of non-Euclidean tetrahedra using tools from algebraic geometry. We establish a bijection between non-Euclidean tetrahedra and certain rational elliptic surfaces. We interpret the edge lengths and the dihedral angles of a tetrahedron as values of period maps for the corresponding surface. As a corollary we show that the cross-ratio of the exponents of the solid angles of a tetrahedron is equal to the cross-ratio of the exponents of the perimeters of its faces. The Regge symmetries of a tetrahedron are related to the action of the Weyl group $$W(D_6)$$ on the Picard lattice of the corresponding surface.

Del Pezzo surfaces with a single $1/k(1,1)$ singularity

Inspired by the recent progress by Coates–Corti–Kasprzyk et al. on mirror symmetry for del Pezzo surfaces, we show that for any positive integer $k$ the deformation families of del Pezzo surfaces with a single $1/k(1,1)$ singularity (and no other singular points) fit into a single cascade. Additionally we construct models and toric degenerations of these surfaces embedded in toric varieties in codimension $\leq 2$. Several of these directly generalise constructions of Reid–Suzuki (in the case $k = 3$). We identify a root system in the Picard lattice, and in light of the work of Gross–Hacking–Keel, comment on mirror symmetry for each of these surfaces. Finally we classify all del Pezzo surfaces with certain combinations of $1/k(1,1)$ singularities for $k = 3,5,6$ which admit a toric degeneration.

Arithmetic and geometry of a K3 surface emerging from virtual corrections to Drell–Yan scattering

We study a K3 surface, which appears in the two-loop mixed electroweak-quantum chromodynamic virtual corrections to Drell--Yan scattering. A detailed analysis of the geometric Picard lattice is presented, computing its rank and discriminant in two independent ways: first using explicit divisors on the surface and then using an explicit elliptic fibration. We also study in detail the elliptic fibrations of the surface and use them to provide an explicit Shioda--Inose structure. Moreover, we point out the physical relevance of our results.

Machine Learning Line Bundle Cohomology

AbstractWe investigate different approaches to machine learning of line bundle cohomology on complex surfaces as well as on Calabi‐Yau three‐folds. Standard function learning based on simple fully connected networks with logistic sigmoids is reviewed and its main features and shortcomings are discussed. It has been observed recently that line bundle cohomology can be described by dividing the Picard lattice into certain regions in each of which the cohomology dimension is described by a polynomial formula. Based on this structure, we set up a network capable of identifying the regions and their associated polynomials, thereby effectively generating a conjecture for the correct cohomology formula. For complex surfaces, we also set up a network which learns certain rigid divisors which appear in a recently discovered master formula for cohomology dimensions.

Classification of degenerations and Picard lattices of Kählerian K3 surfaces with symplectic automorphism group

In [1]–[6] we classified the degenerations and Picard lattices of Kählerian K3 surfaces with finite symplectic automorphism groups of high order. This classification was not considered for the remaining groups of small order (, , , , and ) because each of these cases requires very long and difficult considerations and calculations. Here we consider this classification for the dihedral group of order .

Classification of Degenerations and Picard Lattices of Kählerian K3 Surfaces with Symplectic Automorphism Group C4

In the author’s papers of 2013–2018, the degenerations and Picard lattices of Kählerian K3 surfaces with finite symplectic automorphism groups of high order were classified. For the remaining groups of small order—D6, C4, (C2)2, C3, C2, and C1—the classification was not completed because each of these cases requires very long and difficult considerations and calculations. The case of D6 was recently completely studied in the author’s paper of 2019. In the present paper an analogous complete classification is presented for the cyclic group C4 of order 4.

Families of $K3$ surfaces and curves of (2,3)-torus type

We study families of $K3$ surfaces obtained by double covering of the projective plane branching along curves of (2,3)-torus type. In the first part, we study the Picard lattices of the families, and a lattice duality of them. In the second part, we describe a deformation of singularities of Gorenstein $K3$ surfaces in these families.

Finiteness results for K3 surfaces over arbitrary fields

Over an algebraically closed field, various finiteness results are known regarding the automorphism group of a K3 surface and the action of the automorphisms on the Picard lattice. We formulate and prove versions of these results over arbitrary base fields, and give examples illustrating how behaviour can differ from the algebraically closed case.

Equivalences of families of stacky toric Calabi-Yau hypersurfaces

Given the same anti-canonical linear system on two distinct toric varieties, we provide a derived equivalence between partial crepant resolutions of the corresponding stacky hypersurfaces. The applications include: a derived unification of toric mirror constructions, calculations of Picard lattices for linear systems of quartics in $\mathbf {P}^3$, and a birational reduction of Reid’s list to 81 families.

Classification of Picard lattices of K3 surfaces

Using the results of our papers [1]–[4] on the classification of degenerations of Kählerian K3 surfaces, we classify the Picard lattices of Kählerian K3 surfaces. By classification we mean classification depending on their possible finite symplectic automorphism groups and their non- singular rational curves when the Picard lattice is negative definite.

On the arithmetic of a family of degree - two K3 surfaces

AbstractLet ℙ denote the weighted projective space with weights (1, 1, 1, 3) over the rationals, with coordinates x, y, z and w; let $\mathcal{X}$ be the generic element of the family of surfaces in ℙ given by \begin{equation*} X\colon w^2=x^6+y^6+z^6+tx^2y^2z^2. \end{equation*} The surface $\mathcal{X}$ is a K3 surface over the function field ℚ(t). In this paper, we explicitly compute the geometric Picard lattice of $\mathcal{X}$, together with its Galois module structure, as well as derive more results on the arithmetic of $\mathcal{X}$ and other elements of the family X.

Curves on Heisenberg invariant quartic surfaces in projective 3-space

This paper is about the family of smooth quartic surfaces that are invariant under the Heisenberg group H_{2,2}. For a very generic X, we show that the Picard number of X is 16 and determine its Picard lattice. It turns out that a very generic X contains 320 irreducible conics which generate the Picard group of X.