The intersection of a quadric and a cubic surface in 3-space is a canonical curve of genus 4. It has 120 complex tritangent planes. We present algorithms for computing real tritangents, and we study the associated discriminants. We focus on space sextics that arise from del Pezzo surfaces of degree one. Their numbers of planes that are tangent at three real points vary widely; both 0 and 120 are attained. This solves a problem suggested by Arnold Emch in 1928.
We study SUSY $N$-supergroups, $N=1,2$, their classification and explicit realization, together with their real forms. In the end, we give the supergroup of SUSY preserving automorphism of $mathbf{C}^{1|1}$ and we identify it with a subsupergroup of the SUSY preserving automorphisms of $mathbf{P}^{1|1}$.
We use covariants of binary sextics to describe the structure of modules of scalar-valued or vector-valued Siegel modular forms of degree 2 with character, over the ring of scalar-valued Siegel modular forms of even weight. For a modular form defined by a covariant we express the order of vanishing along the locus of products of elliptic curves in terms of the covariant.
We examine quadratic surfaces in 3-space that are tangent to nine given figures. These figures can be points, lines, planes or quadrics. The numbers of tangent quadrics were determined by Hermann Schubert in 1879. We study the associated systems of polynomial equations, also in the space of complete quadrics, and we solve them using certified numerical methods. Our aim is to show that Schuberts problems are fully real.
We extend Igusas description of the relation between invariants of binary sextics and Siegel modular forms of degree two to a relation between covariants and vector-valued Siegel modular forms of degree two. We show how this relation can be used to effectively calculate the Fourier expansions of Siegel modular forms of degree two.
We consider the family $mathrm{MP}_d$ of affine conjugacy classes of polynomial maps of one complex variable with degree $d geq 2$, and study the map $Phi_d:mathrm{MP}_dto widetilde{Lambda}_d subset mathbb{C}^d / mathfrak{S}_d$ which maps each $f in mathrm{MP}_d$ to the set of fixed-point multipliers of $f$. We show that the local fiber structure of the map $Phi_d$ around $bar{lambda} in widetilde{Lambda}_d$ is completely determined by certain two sets $mathcal{I}(lambda)$ and $mathcal{K}(lambda)$ which are subsets of the power set of ${1,2,ldots,d }$. Moreover for any $bar{lambda} in widetilde{Lambda}_d$, we give an algorithm for counting the number of elements of each fiber $Phi_d^{-1}left(bar{lambda}right)$ only by using $mathcal{I}(lambda)$ and $mathcal{K}(lambda)$. It can be carried out in finitely many steps, and often by hand.