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In this article, we construct countably many mutually non-isotopic diffeomorphisms of some closed non simply-connected 4-manifolds that are homotopic to but not isotopic to the identity, by surgery along $\Theta$-graphs. As corollaries of…

Geometric Topology · Mathematics 2023-02-24 Tadayuki Watanabe

A generic strictly semistable bundle of degree zero over a curve X has a reducible theta divisor, given by the sum of the theta divisors of the stable summands of the associated graded bundle. The converse is not true: Beauville and Raynaud…

Algebraic Geometry · Mathematics 2013-06-11 George H. Hitching , With an appendix by Christian Pauly

In this paper we give a birational model for the theta divisor of the intermediate Jacobian of a generic cubic threefold $X$. We use the standard realization of $X$ as a conic bundle and a $4-$dimensional family of plane quartics which are…

Algebraic Geometry · Mathematics 2007-05-23 Michela Artebani , Remke Kloosterman , Marco Pacini

We construct a Thom class in complex equivariant elliptic cohomology extending the equivariant Witten genus. This gives a new proof of the rigidity of the Witten genus, which exhibits a close relationship to recent work on non-equivariant…

Algebraic Topology · Mathematics 2007-05-23 Matthew Ando , Maria Basterra

Theta functions were defined for varieties with effective anticanonical divisor and are related to certain punctured Gromov-Witten invariants. In this paper we show that in the case of a log Calabi-Yau surface (X,D) with smooth very ample…

Algebraic Geometry · Mathematics 2022-04-27 Tim Graefnitz

We carry out a complete birational classification of the universal theta divisor Th_g over the moduli space of curves of genus g, and show that Th_g enjoys good rationality properties for g<12, and is a variety of general type for g\geq 12.…

Algebraic Geometry · Mathematics 2016-11-22 Gavril Farkas , Alessandro Verra

We study the Albanese image of a compact K\"ahler manifold whose geometric genus is one. We prove that if the Albanese map is not surjective, then the manifold maps surjectively onto an ample divisor in some abelian variety, and in many…

Algebraic Geometry · Mathematics 2016-04-28 Jungkai Chen , Zhi Jiang , Zhiyu Tian

We show that the smooth theta divisors of general principally polarised abelian varieties can be chosen as irreducible algebraic representatives of the coefficients of the Chern-Dold character in complex cobordisms and describe the action…

Algebraic Topology · Mathematics 2024-05-07 V. M. Buchstaber , A. P. Veselov

Let C be a curve of genus g, and let SU(r) be the moduli space of vector bundles of rank r on C, with trivial determinant. A general E in SU(r) defines a theta divisor in the linear system |r Theta|, where Theta is the canonical theta…

Algebraic Geometry · Mathematics 2007-05-23 Arnaud Beauville

In this text we prove that if an abelian variety $A$ admits of an embedding into the Jacobian of a smooth projective curve $C$, and if we consider $\Th_A$ to be the divisor $\Th_C\cap A$, where $\Th_C$ denotes the theta divisor of $J(C)$,…

Algebraic Geometry · Mathematics 2018-04-19 Kalyan Banerjee

We study base points of the generalized Theta-divisor on the moduli space of vector bundles on a smooth algebraic curve X of genus g defined over an algebraically closed field. To do so, we use the derived categories D(Pic(X)), D(Jac(X)),…

Algebraic Geometry · Mathematics 2007-05-23 Georg Hein

We survey the geometry of the theta divisor and discuss various loci of principally polarized abelian varieties (ppav) defined by imposing conditions on its singularities. The loci defined in this way include the (generalized)…

Algebraic Geometry · Mathematics 2013-03-27 Samuel Grushevsky , Klaus Hulek

In this paper we discuss a pair of polynomial knot invariants $\Theta=(\Delta,\theta)$ which is: * Theoretically and practically fast: $\Theta$ can be computed in polynomial time. We can compute it in full on random knots with over 300…

Geometric Topology · Mathematics 2026-05-07 Dror Bar-Natan , Roland van der Veen

We show that the moduli space $\overline{M}_X(v)$ of Gieseker stable sheaves on a smooth cubic threefold $X$ with Chern character $v = (3,-H,-H^2/2,H^3/6)$ is smooth and of dimension four. Moreover, the Abel-Jacobi map to the intermediate…

We compute all the top intersection numbers of divisors on the total space of the Poincare bundle restricted to the product of a curve and the abelian variety. We use these computations to find the class of the universal theta divisor and…

Algebraic Geometry · Mathematics 2010-04-06 Samuel Grushevsky , David Lehavi

Let T be a general bidegree (2,2) divisor in the product of two projective planes. Recently A.Verra proved that the existence of two conic bundle structures (c.b.s.) on T implies a new counterexample to the Torelli theorem for Prym…

alg-geom · Mathematics 2008-02-03 Atanas Iliev

Mimicking the idea of the generalized Hamming weight of linear codes, we introduce a new lattice invariant, the generalized theta series. Applications range from identifying stable lattices to the lattice isomorphism problem. Moreover, we…

Information Theory · Computer Science 2025-07-31 Maiara F. Bollauf , Hsuan-Yin Lin

We study the cohomology groups $H^1(X,\Theta_X(-mK_X))$, for $m\geq1$, where $X$ is a smooth minimal complex surface of general type, $\Theta_X$ its holomorphic tangent bundle, and $K_X$ its canonical divisor. One of the main results is a…

Algebraic Geometry · Mathematics 2011-11-23 Daniel Naie , Igor Reider

We define the theta group associated to a simple coherent sheaf $\cal F$ on a hyperk\"ahler manifold $X$ of Kummer type or OG6 type, provided $g^{*}({\cal F})$ is isomorphic to $\cal F$ for every automorphism $g$ of $X$ acting trivially on…

Algebraic Geometry · Mathematics 2023-04-11 Kieran G. O'Grady

To any homogeneous polynomial $h$ we naturally associate a variety $\Omega_h$ which maps birationally onto the graph $\Gamma_h$ of the gradient map $\nabla h$ and which agrees with the space of complete quadrics when $h$ is the determinant…

Algebraic Geometry · Mathematics 2022-01-25 Abeer Al Ahmadieh , Mario Kummer , Miruna-Stefana Sorea