1,720,974 research outputs found
Riemann-Roch theorems and elliptic genus for virtually smooth schemes
Full text linkFor a proper scheme X with a fixed 1-perfect obstruction theory, we define virtual versions of holomorphic Euler characteristic, chi y-genus, and elliptic genus; they are deformation invariant, and extend the usual definition in the smooth case. We prove virtual versions of the Grothendieck-Riemann-Roch and Hirzebruch-Riemann-Roch theorems. We show that the virtual chi y-genus is a polynomial, and use this to define a virtual topological Euler characteristic. We prove that the virtual elliptic genus satisfies a Jacobi modularity property; we state and prove a localization theorem in the toric equivariant case. We show how some of our results apply to moduli spaces of stable sheaves
On the superadditivity of secant defects
Full text linkIn his paper [Z2], ZAK stated a theorem of superadditivity for secant defects of smooth projective varieties: subsequently, ADLANDSVIK gave a counterexample. In this paper we state and prove a theorem similar to ZAK's but with stronger hypotheses, we show that these do not hold for Adlandsvik's counterexample, and we point out that all of ZAK's corollaries are still implied by our version of the theorem
Orbifold cohomology for global quotients
No full textFor an orbifold X which is the quotient of a manifold Y by a finite group G we construct a noncommutative ring with an action of G such that the orbifold cohomology of X as defined in math.AG/0004129 by Chen and Ruan is the G invariant part. In the case thar Y is S^n for a surface S with trivial canonical class we prove that (a small modification of) the orbifold cohomology of X is naturally isomorphic to the cohomology ring of the Hilbert scheme of n points on S computed in math.AG/0012166 by Lehn and Sorger
Gerstenhaber and Batalin-Vilkovisky structures on Lagrangian intersections
No full textLet M and N be Lagrangian submanifolds of a complex symplectic manifold S . We construct a Gerstenhaber algebra structure on and a compatible Batalin–Vilkovisky module structure on . This gives rise to a de Rham type cohomology theory for Lagrangian intersections
Smoothing semi-smooth stable Godeaux surfaces
Full text linkWe show that all the semi-smooth stable complex Godeaux surfaces, classified in
[M. Franciosi, R. Pardini and S. Rollenske, Ark. Mat. 56 (2018), no. 2, 299–317], are
smoothable and that the moduli stack is smooth of the expected dimension 8 at the
corresponding points
On the Hilbert scheme of curves in higher-dimensional projective space
No full textIn this paper we prove that, for any n ≥ 3, there exist infinitely many r ∈ N and for each of them a smooth, connected curve Crin ℙrsuch that Crlies on exactly n irreducible components of the Hilbert scheme Hilb(ℙr). This is proven by reducing the problem to an analogous statement for the moduli of surfaces of general type
Automorphisms and moduli spaces of varieties with ample canonical class via deformations of abelian covers
No full textBy a recent result of Viehweg, protective manifolds with ample canonical class have a coarse moduli space, which is a union of quasiprojective varieties. In this paper, we prove that there are manifolds with ample canonical class that lie on arbitrarily many irreducible components of the moduli; moreover, for any finite abelian group G there exist infinitely many components M of the moduli of varieties with ample canonical class such that the generic automorphism group GMis equal to G. In order to construct the examples, we use abelian covers. Let Y be a smooth complex projective variety of dimension ≥ 2. A Galois cover f : X → y whose Galois group is finite and abelian is called an abelian cover of Y; by [Pa1], it is determined by its building data, i.e. by the branch divisors and by some line bundles on Y, satisfying appropriate compatibility conditions. Natural deformations of an abelian cover are also introduced in [Pa1]. In this paper we prove two results about abelian covers: first, that if the building data are sufficiently ample, then the natural deformations surject on the Kuranishi family of X; second, that if the building data are sufficiently ample and generic, then Aut(X) = G. Copyright © 1997 by Marcel Dekker, Inc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
