Versal Deformations and Algebraic Stacks.
We extend to compact Kaehler and Fujiki manifolds the theorem of F. Bogomolov, on vanishing of the space of holomorphic p-forms with values in a line bundle whose dual L is numerically effective, for the degrees p less than the numerical dimension of L.
We construct a certain algebro-geometric version of the free loop space for a complex algebraic variety X. This is an ind-scheme containing the scheme of formal arcs in X as studied by Kontsevich and Denef-Loeser. We describe the chiral de Rham complex of Malikov, Schechtman and Vaintrob in terms of the space of formal distributions on supported in . We also show that possesses a factorization structure: a certain non-linear version of a vertex algebra structure. This explains the heuristic...
Quite recently, Alexeev and Nakamura proved that if Y is a stable semi-Abelic variety (SSAV) of dimension g equipped with the ample line bundle OY(1), which deforms to a principally polarized Abelian variety, then OY(n) is very ample as soon as n ≥ 2g + 1, that is n ≥ 5 in the case of surfaces. Here it is proved, via elementary methods of projective geometry, that in the case of surfaces this bound can be improved to n ≥ 3.
This paper is devoted to the study of the volcanoes of ℓ-isogenies of elliptic curves over a finite field, focusing on their height as well as on the location of curves across its different levels. The core of the paper lies on the relationship between the ℓ-Sylow subgroup of an elliptic curve and the level of the volcano where it is placed. The particular case ℓ = 3 is studied in detail, giving an algorithm to determine the volcano of 3-isogenies of a given elliptic curve. Experimental results...