Note about holomorphic maps on a compact Riemann surface
Note to a paper of M. Tanabe concerning the classical theorem of M. De Franchis and F. Severi
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arXiv subjects
Lucio Guerra
Publications and source records attributed to Lucio Guerra.
On Abelian subvarieties of bounded degree in a polarized Abelian variety
If A is an Abelian variety, endowed with a polarization L, we study the function N_A(t) which counts the number of Abelian subvarieties S in A such that for the induced polarization L|_S the Euler characteristic χ(L|_S) is bounded above by t. We give an estimate for the asymptotic order of growth of this function.
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Elliptic curves of bounded degree in a polarized Abelian variety
For a polarized complex Abelian variety A, of dimension g>1, we study the function N_A(t) counting the number of elliptic curves in A with degree bounded by t. We describe elliptic curves as solutions of Diophantine equations which, at least for small dimensions g=2 and g=3, can actually be made explicit, and we show that computing the number of solutions is reduced to the classical topic in Number Theory of counting points of the lattice Z^n lying on an explicit bounded subset of R^n. We obtain, for Abelian varieties of small dimension, some upper bounds for the counting function.
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Parametrization of rational maps on a variety of general type, and the finiteness theorem
In a previous paper, we provided some update in the treatment of the finiteness theorem for rational maps of finite degree from a fixed variety to varieties of general type. In the present paper we present another improvement, introducing the natural parametrization of maps by means of the space of linear projections in a suitable projective space, and this leads to some new insight in the geometry of the finiteness theorem.
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On the finiteness theorem for rational maps on a variety of general type
The dominant rational maps of finite degree from a fixed variety to varieties of general type, up to birational isomorphisms, form a finite set. This has been known as the Iitaka-Severi conjecture, and is nowdays an established result, in virtue of some recent advances in the theory of pluricanonical maps. We study the question of finding some effective estimate for the finite number of maps, and to this aim we provide some update and refinement of the classical treatment of the subject.
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On rational maps from a general surface in P^3 to surfaces of general type
We study the dominant rational maps from a general surface in P^{3} to surfaces of general type. We prove restrictions on the target surfaces, and special properties of the rational maps. We show that for a small degree the general surface has no such map. Moreover a slight improvement of a result of Catanese, on the number of moduli of a surface of general type, is also obtained.
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Siegel coordinates and moduli spaces for morphisms of abelian varieties
We describe the moduli spaces of morphisms between polarized complex abelian varieties. The discrete invariants, derived from a Poincare' decomposition of morphisms, are the types of polarizations and of lattice homomorphisms occurring in the decomposition. For a given type of morphisms the moduli variety is irreducible, and is obtained from a product of Siegel spaces modulo the action of a discrete group.
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