Let $alpha$ be a big class on a compact Kahler manifold. We prove that a decomposition $alpha=alpha_1+alpha_2$ into the sum of a modified nef class $alpha_1$ and a pseudoeffective class $alpha_2$ is the divisorial Zariski decomposition of $alpha$ if and only if $operatorname{vol}(alpha)=operatorname{vol}(alpha_1)$. We deduce from this result some properties of full mass currents.
Using Bochner-Martinelli type residual currents we prove some generalizations of Jacobis Residue Formula, which allow proper polynomial maps to have `common zeroes at infinity, in projective or toric situations.
We give new contributions to the existence problem of canonical surfaces of high degree. We construct several families (indeed, connected components of the moduli space) of surfaces $S$ of general type with $p_g=5,6$ whose canonical map has image $Si
gma$ of very high degree, $d=48$ for $p_g=5$, $d=56$ for $p_g=6$. And a connected component of the moduli space consisting of surfaces $S$ with $K^2_S = 40, p_g=4, q=0$ whose canonical map has always degree $geq 2$, and, for the general surface, of degree $2$ onto a canonical surface $Y$ with $K^2_Y = 12, p_g=4, q=0$. The surfaces we consider are SIP s, i.e. surfaces $S$ isogenous to a product of curves $(C_1 times C_2 )/ G$; in our examples the group $G$ is elementary abelian, $G = (mathbb{Z}/m)^k$. We also establish some basic results concerning the canonical maps of any surface isogenous to a product, basing on elementary representation theory.
Given a spherical homogeneous space G/H of minimal rank, we provide a simple procedure to describe its embeddings as varieties with torus action in terms of divisorial fans. The torus in question is obtained as the identity component of the quotient
group N/H, where N is the normalizer of H in G. The resulting Chow quotient is equal to (a blowup of) the simple toroidal compactification of G/(H N^0). In the horospherical case, for example, it is equal to a flag variety, and the slices (coefficients) of the divisorial fan are merely shifts of the colored fan along the colors.
We determine the cycle classes of effective divisors in the compactified Hurwitz spaces of curves of genus g with a linear system of degree d that extend the Maroni divisors on the open Hurwitz space. Our approach uses Chern classes associated to a g
lobal-to-local evaluation map of a vector bundle over a generic $P^1$-bundle over the Hurwitz space.
Eleonora Di Nezza
,Enrica Floris
,Stefano Trapani
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(2015)
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"Divisorial Zariski Decomposition and some properties of full mass currents"
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Eleonora Di Nezza
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