Curves and their fundamental groups
Curves in P² and symplectic packings.
Curves in P2(C) with 1-dimensional symmetry.
In a previous paper we showed that the existence of a 1-parameter symmetry group of a hypersurface X in projective space was equivalent to failure of versality of a certain unfolding. Here we study in detail (reduced) plane curves of degree d ≥ 3, excluding the trivial case of cones. We enumerate all possible group actions -these have to be either semisimple or unipotent- for any degree d. A 2-parameter group can only occur if d = 3. Explicit lists of singularities of the corresponding curves are...
Curves of
Curves of genus 2 and Desargues configurations.
Curves of genus 2, continued fractions, and Somos sequences.
Curves of genus g lying on a g-dimensional Jacobian variety.
Curves of genus seven that do not satisfy the Gieseker-Petri theorem
In the moduli space of curves of genus , , let be the locus of curves that do not satisfy the Gieseker-Petri theorem. In the genus seven case we show that is a divisor in .
Curves of genus ten on K3 surfaces
Curves of maximal genus in .
Curves of minimal genus on a general abelian variety
Curves on a double surface.
Let F be a smooth projective surface contained in a smooth threefold T, and let X be the scheme corresponding to the divisor 2F on T. A locally Cohen-Macaulay curve C included in X gives rise to two effective divisors on F, namely the largest divisor P contained in C intersection F and the curve R residual to C intersection F in C. We show that under suitable hypotheses a general deformation of R and P lifts to a deformation of C on X, and give applications to the study of Hilbert schemes of locally...
Curves on a ruled cubic surface.
For the general ruled cubic surface S (with a double line) in P3 = P3 sub k, k any algebraically closed field, we find necessary conditions for which curves on S can be the specialization of a flat family of curves on smooth cubics. In particular, no smooth curve of degree > 10 on S is such a specialization.
Curves on a smooth quadric.
We associate to every curve on a smooth quadric a polynomial equation that defines it as a divisor; this polynomial is defined through a matrix. In this way we can study several properties of these curves; in particular we can give a geometrical meaning to the rank of the matrix which defines the curve.
Curves on generic hypersurfaces
Curves on surfaces of degree 2r-... in Pr.
Curves on surfaces with multiple line.
Curves with finite turn
In this paper we study the notions of finite turn of a curve and finite turn of tangents of a curve. We generalize the theory (previously developed by Alexandrov, Pogorelov, and Reshetnyak) of angular turn in Euclidean spaces to curves with values in arbitrary Banach spaces. In particular, we manage to prove the equality of angular turn and angular turn of tangents in Hilbert spaces. One of the implications was only proved in the finite dimensional context previously, and equivalence of finiteness...
Curves with Invertible Hasse-Witt-Matrix.
Curves with only triple ramification
We show that the set of smooth curves of genus admitting a branched covering with only triple ramification points is of dimension at least . In characteristic two, such curves have tame rational functions and an analog of Belyi’s Theorem applies to them.