80 research outputs found
The Geometry and Moduli of K3 Surfaces
These notes will give an introduction to the theory of K3 surfaces. We begin
with some general results on K3 surfaces, including the construction of their
moduli space and some of its properties. We then move on to focus on the theory
of polarized K3 surfaces, studying their moduli, degenerations and the
compactification problem. This theory is then further enhanced to a discussion
of lattice polarized K3 surfaces, which provide a rich source of explicit
examples, including a large class of lattice polarizations coming from elliptic
fibrations. Finally, we conclude by discussing the ample and Kahler cones of K3
surfaces, and give some of their applications.Comment: 34 pages, 2 figures. (R. Laza, M. Schutt and N. Yui, eds.
The Kodaira dimension of the moduli of K3 surfaces
The moduli space of polarised K3 surfaces of degree 2d is a quasi-projective
variety of dimension 19. For general d very little has been known about the
Kodaira dimension of these varieties. In this paper we present an almost
complete solution to this problem. Our main result says that this moduli space
is of general type for d>61 and for d=46,50,54,58,60.Comment: 47 page
Symplectic involutions on deformations of K3^[2]
Let X be a Hyperk\"{a}hler variety deformation equivalent to the Hilbert
square on a K3 surface and let f be an involution preserving the symplectic
form. We prove that the fixed locus of f consists of 28 isolated points and 1
K3 surface, moreover the anti-invariant lattice of the induced involution on
H^2(X,Z) is isomorphic to E_8(-2). Finally we prove that any couple consisting
of one such variety and a symplectic involution on it can be deformed into a
couple consisting of the Hilbert square of a K3 surface and the involution
induced by a Nikulin involution on the K3 surface.Comment: Final version, to appear on Central European Journal of Mathematic
Classification of K3-surfaces with involution and maximal symplectic symmetry
K3-surfaces with antisymplectic involution and compatible symplectic actions
of finite groups are considered. In this situation actions of large finite
groups of symplectic transformations are shown to arise via double covers of
Del Pezzo surfaces. A complete classification of K3-surfaces with maximal
symplectic symmetry is obtained.Comment: 26 pages; final publication available at http://www.springerlink.co
Families of Quintic Calabi-Yau 3-Folds with Discrete Symmetries
At special loci in their moduli spaces, Calabi-Yau manifolds are endowed with
discrete symmetries. Over the years, such spaces have been intensely studied
and have found a variety of important applications. As string compactifications
they are phenomenologically favored, and considerably simplify many important
calculations. Mathematically, they provided the framework for the first
construction of mirror manifolds, and the resulting rational curve counts.
Thus, it is of significant interest to investigate such manifolds further. In
this paper, we consider several unexplored loci within familiar families of
Calabi-Yau hypersurfaces that have large but unexpected discrete symmetry
groups. By deriving, correcting, and generalizing a technique similar to that
of Candelas, de la Ossa and Rodriguez-Villegas, we find a calculationally
tractable means of finding the Picard-Fuchs equations satisfied by the periods
of all 3-forms in these families. To provide a modest point of comparison, we
then briefly investigate the relation between the size of the symmetry group
along these loci and the number of nonzero Yukawa couplings. We include an
introductory exposition of the mathematics involved, intended to be accessible
to physicists, in order to make the discussion self-contained.Comment: 54 pages, 3 figure
K3 surfaces and log del Pezzo surfaces of index three
We use classification of non-symplectic automorphisms of K3 surfaces to
obtain a partial classification of log del Pezzo surfaces of index three. We
can classify those with "Multiple Smooth Divisor Property", whose definition we
will give. Our methods include the definition of right resolutions of quotient
singularities of index three and some analysis of automorphism-stable elliptic
fibrations on K3 surfaces. In particular we find several log del Pezzo surfaces
of Picard number one with non-toric singularities of index three.Comment: 32 pages, to appear in Manuscripta Mat
On the 0-dimensional cusps of the Kahler moduli of a K3 surface
Let S be a projective K3 surface. It is proved that the 0-dimensional cusps
of the Kahler moduli of S are in one-to-one correspondence with the twisted
Fourier-Mukai partners of S. This leads to a counting formula for the
0-dimensional cusps of the Kahler moduli. Applications to rational maps between
K3 surfaces with large Picard numbers are given. When the Picard number of S is
1, the bijective correspondence is calculated explicitly.Comment: 24page
Wave kinetics of random fibre lasers
Traditional wave kinetics describes the slow evolution of systems with many degrees of freedom to equilibrium via numerous weak non-linear interactions and fails for very important class of dissipative (active) optical systems with cyclic gain and losses, such as lasers with non-linear intracavity dynamics. Here we introduce a conceptually new class of cyclic wave systems, characterized by non-uniform double-scale dynamics with strong periodic changes of the energy spectrum and slow evolution from cycle to cycle to a statistically steady state. Taking a practically important example—random fibre laser—we show that a model describing such a system is close to integrable non-linear Schrödinger equation and needs a new formalism of wave kinetics, developed here. We derive a non-linear kinetic theory of the laser spectrum, generalizing the seminal linear model of Schawlow and Townes. Experimental results agree with our theory. The work has implications for describing kinetics of cyclical systems beyond photonics
Lagrangian fibrations of holomorphic-symplectic varieties of K3^[n]-type
Let X be a compact Kahler holomorphic-symplectic manifold, which is
deformation equivalent to the Hilbert scheme of length n subschemes of a K3
surface. Let L be a nef line-bundle on X, such that the 2n-th power of c_1(L)
vanishes and c_1(L) is primitive. Assume that the two dimensional subspace
H^{2,0}(X) + H^{0,2}(X), of the second cohomology of X with complex
coefficients, intersects trivially the integral cohomology. We prove that the
linear system of L is base point free and it induces a Lagrangian fibration on
X. In particular, the line-bundle L is effective. A determination of the
semi-group of effective divisor classes on X follows, when X is projective. For
a generic such pair (X,L), not necessarily projective, we show that X is
bimeromorphic to a Tate-Shafarevich twist of a moduli space of stable torsion
sheaves, each with pure one dimensional support, on a projective K3 surface.Comment: 34 pages. v3: Reference [Mat5] and Remark 1.8 added. Incorporated
improvement to the exposition and corrected typos according to the referees
suggestions. To appear in the proceedings of the conference Algebraic and
Complex Geometry, Hannover 201
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