arXiv subjects

Viacheslav V. Nikulin

Publications and source records attributed to Viacheslav V. Nikulin.

At least 37 records · Page 2Linked to original sources

arXiv2006

Classification of log del Pezzo surfaces of index $\le 2$

This is an expanded version of our work [AN88], 1988, in Russian. We classify del Pezzo surfaces over C with log terminal singularities of index \le 2. By classification, we understand a description of the intersection graph of all exceptional curves on an appropriate (somewhat stronger than minimal) resolution of singularities together with the subgraph of the curves which are contracted to singular points. The final results are similar to classical results about classification of non-singular del Pezzo surfaces and use the usual finite root systems. However, the intermediate considerations use the theory of K3 surfaces (especially of K3 surfaces with non-symplectic involutions) and the theory of reflection groups in hyperbolic spaces (especially or reflection groups of hyperbolic lattices). As an ``elementary'' application, our results permit one to classify sextics in P^2 with simple singularities and a component of geometric genus \ge 2.

math.AG↗

arXiv2006

On correspondences of a K3 surface with itself. III

Let $X$ be a K3 surface, and $H$ its primitive polarization of the degree $H^2=2rs$, $r,s\ge 1$. The moduli space of sheaves over $X$ with the isotropic Mukai vector $(r,H,s)$ is again a K3 surface, $Y$. In math.AG/0206158, math.AG/0304415 and math.AG/0307355 (in general) we gave necessary and sufficient conditions in terms of Picard lattice $N(X)$ of $X$ when $Y$ is isomorphic to $X$, under the additional condition $H\cdot N(X)=\bz$. Here we show that these conditions imply existence of an isomorphism between $Y$ and $X$ which is a composition of some universal isomorphisms between moduli of sheaves over $X$, and Tyurin's isomorphsim between moduli of sheaves over $X$ and $X$ itself. It follows that for a general K3 surface $X$ with $H\cdot N(X)=\bz$ and $Y\cong X$, there exists an isomorphism $Y\cong X$ which is a composition of the universal and the Tyurin's isomorphisms. This generalizes our recent results math.AG/0605362 for $r=s=2$ on similar subject.

math.AG↗

arXiv2005

Real K3 surfaces with non-symplectic involution and applications. II

We consider real forms of relatively minimal rational surfaces F_m. Connected components of moduli of real non-singular curves in |-2K_{F_m}| had been classified recently for m=0, 1, 4 in math.AG/0312396. Applying similar methods, here we fill the gap for m=2 and m=3 to complete similar classification for any 0\le m\le 4 when |-2K_{F_m}| is reduced. The case of F_2 is especially remarkable and classical (quadratic cone in P^3). As an application, we finished classification of connected components of moduli of real hyper-elliptically polarized K3 surfaces and their deformations to real polarized K3 surfaces started in math.AG/0312396, math.AG/0507197. This could be important in some questions because real hyper-elliptically polarized K3 surfaces can be constructed explicitly.

math.AG↗

arXiv2005

Remarks on connected components of moduli of real polarized K3 surfaces

I have finalized my old (1979) results about enumeration of connected components of moduli of real polarized K3 surfaces. As an application, using recent results of math.AG/0312396, the complete classification of real polarized K3 surfaces which are deformations of real hyper-elliptically polarized K3 surfaces is obtained. This could be important in some questions, because real hyper-elliptically polarized K3 surfaces can be constructed explicitly.

math.AG↗

arXiv2005

On Correspondences of a K3 Surface with itself, II

Let X be a K3 surface with a polarization H of degree H^2=2rs and with a primitive Mukai vector (r,H,s). The moduli space of sheaves over X with the isotropic Mukai vector (r,H,s) is again a K3 surface Y. We prove that Y\cong X, if Picard lattice N(X) has an element h_1 with h_1^2=f(r,s), and the pair (H,h_1) satisfies a finite number of congruence conditions modulo N_i(r,s). These conditions are exactly written and are necessary for Y\cong X, if X is general with rk N(X)=2. Existence of such criterion is surprising and gives some geometric interpretation of elements in N(X) with negative square. We also desribe all divisorial conditions on moduli of (X,H) which imply Y\cong X. Thus, here we treat in general problems considered in math.AG/0206158, math.AG/0304415, math.AG/0307355 when H.N(X)=Z was assumed. In general, the results are much more complicated and less efficient.

math.AG↗

arXiv2003

Real K3 Surfaces with non-symplectic Involutions and Applications

Classification of real K3 surfaces X with a non-symplectic involution τis considered. For some exactly defined and one of the weakest possible type of degeneration (giving the very reach discriminant), we show that the connected component of their moduli is defined by the isomorphism class of the action of τand the anti-holomorphic involution ϕin the homology lattice. (There are very few similar cases known.) For their classification we apply invariants of integral lattice involutions with conditions which were developed by the first author in 1983. As a particular case, we describe connected components of moduli of real non-singular curves A\in |-2K_V| for the classical real surfaces: V=P^2, hyperboloid, ellipsoid, F_1, F_4. As an application, we describe all real polarized K3 surfaces which are deformations of general real K3 double rational scrolls (surfaces V above). There are very few exceptions. For example, any non-singular real quartic in P^3 can be constructed in this way.

math.AG↗

arXiv2003

On Correspondences of a K3 Surface with itself I

Let X be a K3 surface with a polarization H with H^2=2rs. Assume that H.N(X)=Z for the Picard lattice N(X). The moduli space Y of sheaves over X with the Mukai vector (r,H,s) is again a K3 surface. We prove that Y\cong X, if there exists h_1\in N(X) with (h_1)^2=f(r,s), H.h_1\equiv 0\mod g(r,s), and h_1 satisfies some condition of primitivity. Existence of such type a criterion is surprising, and also gives some geometric interpretation of elements in N(X) with negative square. We describe all 18-dimensional irreducible components of moduli of the (X,H) with Y\cong X and prove that their number is infinite. These generalizes results of math.AG/0206158, math.AG/0304415 for r=s.

math.AG↗

arXiv2003

On a classical correspondence between K3 surfaces II

Let X be a K3 surface and H a primitive polarization of degree H^2=2a^2, a>1. The moduli space of sheaves over X with the isotropic Mukai vector (a,H,a) is again a K3 surface Y which is endowed by a natural nef element h with h^2=2. We give necessary and sufficient conditions in terms of Picard lattices N(X) and N(Y) when Y\cong X, generalising our results math.AG/0206158 for a=2. E.g. we show that Y\cong X if for one of α=\pm 1,\pm 2 which is coprime to a there exists h_1\in N(X) such that h_1^2= 2αa, H\cdot h_1\equiv 0\mod αa, and the primitive sublattice [H,h_1]_{pr} \subset N(X) contains x such that $x\cdot H=1$. We find all divisorial conditions on moduli of (X,H) (i.e for Picard number 2) which imply Y\cong X and H\cdot N(X)=Z. Some of these conditions were found in different form by A.N. Tyurin in 1987.

math.AG↗

arXiv2003

On algebraic varieties with finite polyhedral Mori cone

The fundamental property of Fano varieties with mild singularities is that they have a finite polyhedral Mori cone. Thus, it is very interesting to ask: What we can say about algebraic varieties with a finite polyhedral Mori cone? I give a review of known results. All of them were obtained applying methods which were originated in the theory of discrete groups generated by reflections in hyperbolic spaces with a fundamental chamber of finite volume. This is my report on Fano conference in Torino, October 2002

math.AG↗

arXiv2002

On a classical correspondence between K3 surfaces

Let X be a K3 surface which is intersection of three (a net P^2) of quadrics in P^5. The curve of degenerate quadrics has degree 6 and defines a double covering of P^2 K3 surface Y ramified in this curve. This is a classical example of a correspondence between K3 surfaces which is related with moduli of vector bundles on K3 studied by Mukai. When general (for fixed Picard lattices) X and Y are isomorphic? We give necessary and sufficient conditions in terms of Picard lattices of X and Y. E.g. for Picard number 2, the Picard lattice of X and Y is defined by its determinant (-d) where d>0, d\equiv 1 \mod 8, and one of equations a^2-db^2=8 or a^2-db^2=-8 should have an integral solution (a,b). The set of these d is infinite: d\in {(a^2\mp 8)/b^2} where a and b are odd integers. This describes all possible divisorial conditions on 19- dimensional moduli of intersections of three quadrics in P^5 when Y\cong X. One of them when X has a line is classical, and corresponds to d=17. Similar considerations can be applied for a realization of an isomorphism (T(X)\otimes Q, H^{2,0}(X)) \cong (T(Y)\otimes Q, H^{2,0}(Y)) of transcendental periods over Q of two K3 surfaces X and Y by a fixed sequence of types of Mukai vectors.

math.AG↗

arXiv2002

On classification of Lorentzian Kac-Moody algebras

We discuss a general theory of Lorentzian Kac--Moody algebras which should be a hyperbolic analogy of the classical theories of finite-dimensional semi-simple and affine Kac-Moody algebras. First examples of Lorentzian Kac-Moody algebras were found by Borcherds. We consider general finiteness results about the set of Lorentzian Kac--Moody algebras and the problem of their classification. As an example, we give classification of Lorentzian Kac--Moody algebras of the rank three with the symmetry group which is an extended paramodular group. Perhaps, this is the first example when a large class of Lorentzian Kac--Moody algebras was classified. This paper is closely related with our papers math.AG/9810001, math.AG/0010329

math.QA↗

arXiv2000

A Lecture about classification of Lorentzian Kac-Moody algebras of the rank three

This is the announcement and partly the review of our results about classification of Lorentzian Kac-Moody algebras of the rank three. One of our results gives the classification of Lorentzian Kac-Moody algebras with denominator identity functions which are holomorphic reflective automorphic forms with respect to paramodular groups. Almost all of them were found in our paper ``Automorphic forms and Lorentzian Kac-Moody algebras. Parts I, II'', Intern. J. Math. 9 (1998), 153-275. Our main result gives classification of all reflective meromorphic automorphic products with respect to paramodular groups. This is mainly a presentation of our lectures given during the Workshop: ``Applications to Quantum Field Theory'', October 23 - 27, 2000, in the Newton Mathematical Institute at Cambridge.

math.AG↗

arXiv1999

On the classification of hyperbolic root systems of the rank three. Part III

See Parts I and II in alg-geom/9711032 and alg-geom/9712033. Here we classify maximal hyperbolic root systems of the rank three having restricted arithmetic type and a generalized lattice Weyl vector $ρ$ with $ρ^2<0$ (i. e. of the hyperbolic type). We give classification of all reflective of hyperbolic type elementary hyperbolic lattices of the rank three. For elliptic (when $ρ^2>0$) and parabolic (when $ρ^2=0$) types it was done in Parts I and II. We apply the same arguments as for elliptic and parabolic types: the method of narrow parts of polyhedra in hyperbolic spaces, and class numbers of central symmetries. But we should say that for the hyperbolic type all considerations are much more complicated and required much more calculations and time. These results are important, for example, for Theory of Lorentzian Kac--Moody algebras and some aspects of Mirror Symmetry. We also apply these results to prove boundedness of families of algebraic surfaces with almost finite polyhedral Mori cone (see math.AG/9806047 about this subject).

math.AG↗

arXiv1998

A remark on algebraic surfaces with polyhedral Mori cone

We denote by FPMC the class of all non-singular projective algebraic surfaces X over C with a finite polyhedral Mori cone NE(X)\subset NS(X)\otimes R. If rho(X)=rk NS(X)\ge 3, then the set Exc(X) of all exceptional curves on X\in FPMC is finite and generates NE(X). Let δ_E(X) be the maximum of (-E^2) and p_E(X) the maximum of p_a(E) respectively for E\in Exc(X). For fixed ρ\ge 3, δ_E and p_E we denote by FPMC_{ρ,δ_E,p_E} the class of all X\in FPMC such that ρ(X)=ρ, δ_E(X)=δ_E and p_E(X)=p_E. We prove that the class FPMC_{ρ,δ_E,p_E} is bounded: for any X\in FPMC_{ρ,δ_E,p_E} there exist an ample effective divisor h and a very ample divisor h' such that h^2\le N(ρ,δ_E) and {h'}^2\le N'(ρ,δ_E,p_E) where the constants N(ρ,δ_E)$ and N'(ρ,δ_E,p_E) depend only on (ρ, δ_E) and (ρ, δ_E, p_E) respectively. One can consider Theory of surfaces X\in FPMC as Algebraic Geometry analog of the Theory of arithmetic reflection groups in hyperbolic spaces.

math.AG↗

arXiv1998

A Theory of Lorentzian Kac-Moody algebras

We present a variant of the Theory of Lorentzian (i. e. with a hyperbolic generalized Cartan matrix) Kac-Moody algebras recently developed by V. A. Gritsenko and the author. It is closely related with and strongly uses results of R. Borcherds. This theory should generalize well-known Theories of finite Kac-Moody algebras (i. e. classical semisimple Lie algebras corresponding to positive generalized Cartan matrices) and affine Kac-Moody algebras (corresponding to semi-positive generalized Cartan matrices). Main features of the Theory of Lorentzian Kac-Moody algebras are: One should consider generalized Kac-Moody algebras introduced by Borcherds. Denominator function should be an automorphic form on IV type Hermitian symmetric domain (first example of this type related with Leech lattice was found by Borcherds). The Kac-Moody algebra is graded by an integral hyperbolic lattice $S$. Weyl group acts in the hyperbolic space related with $S$ and has a fundamental polyhedron $\Cal M$ of finite (or almost finite) volume and a lattice Weyl vector. There are results and conjectures which permit (in principle) to get a ``finite'' list of all possible Lorentzian Kac-Moody algebras. Thus, this theory looks very similar to Theories of finite and affine Kac-Moody algebras but is much more complicated. There were obtained some classification results on Lorentzian Kac-Moody algebras and many of them were constructed.

math.AG↗

arXiv1998

On the classification of hyperbolic root systems of the rank three. Part II

Here we prove classification results announced in Part I (alg-geom/9711032). We classify maximal hyperbolic root systems of the rank 3 having restricted arithmetic type and a generalized lattice Weyl vector $ρ$ with $ρ^2\ge 0$ (i.e. of elliptic or parabolic type). We give classification of all reflective of elliptic or parabolic type elementary hyperbolic lattices of the rank three. We apply the same method (narrow places of polyhedra) which was developed to prove finiteness results on reflective hyperbolic lattices. We also use some additional arithmetic arguments: studying of class numbers of central symmetries. The same methods permit to get similar results for hyperbolic type. We will consider hyperbolic type in Part III. These results are important for Theory of Lorentzian Kac--Moody algebras and some aspects of Mirror Symmetry.

alg-geom↗

arXiv1997

On the classification of hyperbolic root systems of the rank three. Part I

It was recently understood that from the point of view of automorphic Lorentzian Kac-Moody algebras and some aspects of Mirror Symmetry, interesting hyperbolic root systems should have restricted arithmetic type and a generalized lattice Weyl vector. One can consider hyperbolic root systems with these properties as an appropriate hyperbolic analog of the classical finite and affine root systems. This series of papers is devoted to classification of hyperbolic root systems of restricted arithmetic type and with a generalized lattice Weyl vector $ρ$, having the rank 3 (it is the first non-trivial rank). In the Part I we announce classification of the maximal hyperbolic root systems of elliptic (i.e. $ρ^2 >0$) and parabolic (i.e. $ρ^2=0$) type, having the rank 3. We give sketch of the proof. Details of the proof and further results (non-maximal cases) will be given in Part II. Classification for hyperbolic type (i.e. $ρ^2<0$) and applications will be considered in Part III.

alg-geom↗

arXiv1997

K3 surfaces with interesting groups of automorphisms

By the fundamental result of I.I. Piatetsky-Shapiro and I.R. Shafarevich (1971), the automorphism group Aut(X) of a K3 surface X over C and its action on the Picard lattice S_X are prescribed by the Picard lattice S_X. We use this result and our method (1980) to show finiteness of the set of Picard lattices S_X of rank $\ge 3$ such that the automorphism group Aut(X) of the K3 surface X has a non-trivial invariant sublattice S_0 in S_X where the group Aut(X) acts as a finite group. For hyperbolic and parabolic lattices S_0 it has been proved by the author before (1980, 1995). Thus we extend this results to negative sublattices S_0. We give several examples of Picard lattices S_X with parabolic and negative S_0. We also formulate the corresponding finiteness result for reflective hyperbolic lattices of hyperbolic type over purely real algebraic number fields. These results are important for the theory of Lorentzian Kac--Moody algebras and Mirror Symmetry.

alg-geom↗