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arXiv2008

Kernel algebras and generalized Fourier-Mukai transforms

We introduce and study kernel algebras, i.e., algebras in the category of sheaves on a square of a scheme, where the latter category is equipped with a monoidal structure via a natural convolution operation. We show that many interesting categories, such as D-modules, equivariant sheaves and their twisted versions, arise as categories of modules over kernel algebras. We develop the techniques of constructing derived equivalences between these module categories. As one application we generalize the results of math.AG/9901009 concerning modules over algebras of twisted differential operators on abelian varieties. As another application we recover and generalize the results of Laumon in alg-geom/9603004 concerning an analog of the Fourier transform for derived categories of quasicoherent sheaves on a dual pair of generalized 1-motives.

math.AG↗

arXiv2009

Equivariant Gromov-Witten theory of one dimensional stacks

In math.AG/0207233, Okounkov and Pandharipande gave an operator formalism for computing the equivariant Gromov-Witten theory of the projective line. This thesis extends their result to orbifold lines. In the effective case the theory is again governed by the 2-Toda hierarchy. In the ineffective case the decomposition conjecture of hep-th/0606034 is verified.

math.AG↗

arXiv2010

Hodge groups of certain superelliptic jacobians

Suppose that $K$ is a field of characteristic 0, $p$ is an odd prime, $r$ a positive integer, $q=p^r$ a prime power. Suppose that $f(x)$ is a polynomial of degree $n > 4$ with coefficients in $K$ and without multiple roots. Let us consider the superelliptic curve $C: y^q=f(x)$ and its jacobian $J(C)$. Assuming that $K$ is a subfield of the field of complex numbers, we study the (connected reductive algebraic) Hodge group $Hdg$ of the corresponding complex abelian variety $J(C)$. In our previous paper (arXiv:0907.1563 [math.AG]) we studied the center of $Hdg. In this paper we study the semisimple part (commutator subgroup) of $Hdg$. Assuming that $p$ does not divide $n$ and $n-1$ is not divisible by $q$, the Galois group of $f(x)$ over $K$ is either the full symmetric group $S_n$ or the alternating group $A_n$, we prove that the semisimple part of $Hdg$ is "as large as possible".

math.AG↗

arXiv2010

Theta groups and products of abelian and rational varieties

We prove that an analogue of Jordan's theorem on finite subgroups of general linear groups does not hold for the groups of birational automorphisms of products of an elliptic curve and the projective line. This gives a negative answer to a question of V. L. Popov, arXiv:1001.1311 [math.AG].

math.AG↗

arXiv2011

From WZW models to Modular Functors

In this survey paper (which supersedes our earlier arXiv preprint math.AG/0507086) we give a relatively simple and coordinate free description of the WZW model as a local system whose base is a G_m-bundle on the moduli stack of pointed curves. We derive its main properties and show how it leads to a modular functor in the spirit of Graeme Segal (except for unitarity). The approach presented here is almost purely algebro-geometric in character; it avoids the Boson-Fermion correspondence, operator product expansions as well as Teichmueller theory.

math.AG↗

arXiv2011

Algebraic cobordism of filtered vector bundles on varieties: Notes on a work of Lee and Pandharipande

The construction of double point cobordism groups of vector bundles on varieties in the work [Lee-P] (arXiv:1002.1500 [math.AG]) of Yuan-Pin Lee and Rahul Pandharipande gives immediately double point cobordism groups of filtered vector bundles on varieties. We note also that among the four basic operations -- direct sum, tensor product, dual, and Hom -- on vector bundles on varieties, only taking dual is compatible with double point cobordisms of vector bundles on varieties in general, by a demonstration on an example of vector bundles on Calabi-Yau 3-folds. A question on refined and/or higher algebraic cobordisms of vector bundles on varieties is posed in the end.

math.AG↗

arXiv2011

To the multidimensional tame symbol

We give a construction of the two-dimensional tame symbol as the commutator of a group-like monoidal groupoid which is obtained from some group of k-linear operators acting in a two-dimensional local field and corresponds to some third cohomology class of this group. We give also the hypothetical method for the proof of the two-dimensional Parshin reciprocity laws. This text was written in 2003 as preprint 03-13 of the Humboldt University of Berlin and was available at http://edoc.hu-berlin.de/docviews/abstract.php?id=26204 (only evident misprints are corrected now). Later E. Frenkel and X. Zhu obtained in arXiv:0810.1487 [math.RT] more general results concerning the third cohomology classes of groups acting on two-dimensional local fields, and the author and X. Zhu obtained in arXiv:1002.4848 [math.AG] the proof of the Parshin reciprocity laws on an algebraic surface similar to the Tate proof of the residue formula on an algebraic curve.

math.AG↗

arXiv2011

On some fibrations of $\overline{M}_{0,n}$

The paper is a second step in the study of $\overline{M}_{0,n}$ started in arXiv:1006.0987 [math.AG]. We study fiber type morphisms of this moduli space via Kapranov's beautiful description. Our final goal is to understand if any dominant morphism $f: \overline{M}_{0,n} \to X$ with positive dimensional fibers factors through forgetful morphisms. We prove that this is true if either $n \leq 7$ or $\rm {dim} X \leq 2$ or the rational map induced on $P^{n-3}$ has linear general fibers. Along the way we give examples of forgetful morphisms whose fibers are connected curves of arbitrarily high positive genus, for $n>>0$.

math.AG↗

arXiv2011

Kunz Regularity Criterion via algebraic entropy

In arXiv:1109.6438v1 [math.AG] we introduced and studied a notion of algebraic entropy. In this paper we will give an application of algebraic entropy in proving Kunz Regularity Criterion for all contracting self-maps of finite length of Noetherian local rings in arbitrary characteristic. Some conditions of Kunz Criterion have already been extended to the general case by Avramov, Iyengar and Miller in arXiv:math/0312412v2 [math.AC], using different methods.

math.AC↗

arXiv2012

Globally Generated Vector Bundles on P^n with c_1=3

One classifies the globally generated vector bundles on P^n (n \not = 3) with the first Chern class c_1 = 3. The case n = 3 is treated in arXiv:1202.5988 [math.AG]. The case c_1 = 2 was treated by J.C. Sierra and L. Ugaglia (see References), the case c_1 = 3, rank = 2 is settled by S. Huh (see References), the case rank = 2, c_1 \le 5 is studied by L. Chiodera and Ph. Ellia (see References).

math.AG↗

arXiv2013

A mathematical theory of D-string world-sheet instantons, I: Compactness of the stack of $Z$-semistable Fourier-Mukai transforms from a compact family of nodal curves to a projective Calabi-Yau 3-fold

In a suitable regime of superstring theory, D-branes in a Calabi-Yau space and their most fundamental behaviors can be nicely described mathematically through morphisms from Azumaya spaces with a fundamental module to that Calabi-Yau space. In the earlier work [L-L-S-Y] (D(2): arXiv:0809.2121 [math.AG], with Si Li and Ruifang Song) from the project, we explored this notion for the case of D1-branes (i.e. D-strings) and laid down some basic ingredients toward understanding the notion of D-string world-sheet instantons in this context. In this continuation, D(10), of D(2), we move on to construct a moduli stack of semistable morphisms from Azumaya nodal curves with a fundamental module to a projective Calabi-Yau 3-fold $Y$. In this Part I of the note, D(10.1), we define the notion of twisted central charge $Z$ for Fourier-Mukai transforms of dimension 1 and width [0] from nodal curves and the associated stability condition on such transforms and prove that for a given compact stack of nodal curves $C_{\cal M}/{\cal M}$, the stack $FM^{1,[0];Zss}_{C_{\cal M}/{\cal M}}(Y,c)$ of $Z$-semistable Fourier-Mukai transforms of dimension 1 and width [0] from nodal curves in the family $C_{\cal M}/{\cal M}$ to $Y$ of fixed twisted central charge $c$ is compact. For the application in the sequel D(10.2), $C_{\cal M}/{\cal M}$ will contain $C_{\bar{\cal M}_g}/\bar{\cal M}_g$ as a substack and $FM^{1,[0];Zss}_{C_{\cal M}/{\cal M}}(Y,c)$ in this case will play a key role in defining stability condition for morphisms from arbitrary Azumaya nodal curves (with the underlying nodal curves not necessary in the family $C_{\cal M}/{\cal M}$) to $Y$.

math.AG↗

arXiv2013

Notes on hyperelliptic fibrations of genus 3, II

This is the part II of the series under the same title. In part I, using the approach developed by Catanese--Pignatelli arXiv:math/0503294, we gave a structure theorem for hyperelliptic genus 3 fibrations all of whose fibers are 2-connected (arXiv:1209.6278 [math.AG]). In this part II, we shall give a structure theorem for smooth deformation families of these to non-hyperelliptic genus 3 fibrations. As an application, we shall give a set of sufficient conditions for our genus 3 hyperelliptic fibration above to allow deformation to non-hyperelliptic fibrations, and use this to study certain minimal regular surfaces with first Chern number 8 and geometric genus 4: we shall find in the moduli space two strata M_0^{sharp} and M_0^{flat}$ (each of dimensions 32 and 30, respectively), and show that Bauer--Pingatelli's stratum M_0 (arXiv:math/0603094) and its 26-dimensional substratum are at the boundary of these new strata M_0^{sharp} and M_0^{flat}, respectively.

math.AG↗

arXiv2014

Wall-crossing in genus zero quasimap theory and mirror maps

For each positive rational number epsilon, the theory of epsilon-stable quasimaps to certain GIT quotients W//G developed in arXiv:1106.3724[math.AG] gives rise to a Cohomological Field Theory. Furthermore, there is an asymptotic theory corresponding to epsilon --> 0. For epsilon >1 one obtains the usual Gromov-Witten theory of W//G, while the other theories are new. However, they are all expected to contain the same information and in particular the numerical invariants should be related by wall-crossing formulas. In this paper we analyze the genus zero picture and find that the wall-crossing in this case significantly generalizes toric mirror symmetry (the toric cases correspond to abelian groups G). In particular, we give a geometric interpretation of the mirror map as a generating series of quasimap invariants. We prove our wall-crossing formulas for all targets W//G which admit a torus action with isolated fixed points, as well as for zero loci of sections of homogeneous vector bundles on such W//G.

math.AG↗

arXiv2013

k-nets embedded in a projective plane over a field

We investigate $k$-nets with $k\geq 4$ embedded in the projective plane $PG(2,\mathbb{K})$ defined over a field $\mathbb{K}$; they are line configurations in $PG(2,\mathbb{K})$ consisting of $k$ pairwise disjoint line-sets, called components, such that any two lines from distinct families are concurrent with exactly one line from each component. The size of each component of a $k$-net is the same, the order of the $k$-net. If $\mathbb{K}$ has zero characteristic, no embedded $k$-net for $k\geq 5$ exists; see [1,2]. Here we prove that this holds true in positive characteristic $p$ as long as $p$ is sufficiently large compared with the order of the $k$-net. Our approach, different from that used in [1,2], also provides a new proof in characteristic zero. [1] J. Stipins, Old and new examples of k-nets in P2, math.AG/0701046. [2] S. Yuzvinsky, A new bound on the number of special fibers in a pencil of curves, Proc. Amer. Math. Soc. 137 (2009), 1641-1648.

math.AG↗

arXiv2013

A mathematical theory of D-string world-sheet instantons, II: Moduli stack of $Z$-(semi)stable morphisms from Azumaya nodal curves with a fundamental module to a projective Calabi-Yau 3-fold

In this Part II, D(10.2), of D(10), we take D(10.1) (arXiv:1302.2054 [math.AG]) as the foundation to define the notion of $Z$-semistable morphisms from general Azumaya nodal curves, of genus $\ge 2$, with a fundamental module to a projective Calabi-Yau 3-fold and show that the moduli stack of such $Z$-semistable morphisms of a fixed type is compact. This gives us a counter moduli stack to D-strings as the moduli stack of stable maps in Gromov-Witten theory to the fundamental string. It serves and prepares for us the basis toward a new invariant of Calabi-Yau 3-fold that captures soft-D-string world-sheet instanton numbers in superstring theory. This note is written hand-in-hand with D(10.1) and is to be read side-by-side with ibidem.

math.AG↗

arXiv2014

Gaussian maps and generic vanishing I: subvarieties of abelian varieties

We present an approach to Green-Lazarsfeld's generic vanishing combining gaussian maps and the Fourier-Mukai transform associated to the Poincarè line bundle. As an application we prove the Generic Vanishing Theorem for all normal Cohen-Macaulay subvarieties of abelian varieties over an algebraically closed field. This paper is a reworking of part of arXiv:math/0310026v2 [math.AG], which contained a mistake.

math.AG↗

arXiv2017

The derived functors of unramified cohomology

We study the first "derived functors of unramified cohomology" in the sense of arXiv:1506.08385 [math.AG], applied to the sheaves $\mathbf{G}_m$ and $\mathcal{K}_2$. We find interesting connections with classical cycle-theoretic invariants of smooth projective varieties, involving notably a version of the Griffiths group, and the indecomposable $(2,1)$-cycles.

math.AG↗

arXiv2016

Dynamics of D-branes I. The non-Abelian Dirac-Born-Infeld action, its first variation, and the equations of motion for D-branes --- with remarks on the non-Abelian Chern-Simons/Wess-Zumino term

In earlier works, D(1) (arXiv:0709.1515 [math.AG]), D(11.1) (arXiv:1406.0929 [math.DG]), D(11.2) (arXiv:1412.0771 [hep-th]), and D(11.3.1) (arXiv:1508.02347 [math.DG]), we have explained why a D-brane in string theory, when treated as a fundamental dynamical object, can be described by a map $φ$ from an Azumaya/matrix manifold $X^{Az}$ (cf. D-brane world-volume) with a fundamental module with a connection $(E,\nabla)$ (cf. Chan-Paton bundle) to the target space-time $Y$. In this sequel, we construct a non-Abelian Dirac-Born-Infeld action functional $S_{DBI}^{(Φ, g, B)}(φ,\nabla)$ for such pairs $(φ,\nabla)$. We next develop a technical tool needed to study variations of this action and apply it to derive the first variation $δS_{DBI}^{(Φ,g,B)}/δ(φ,\nabla)$ of $S_{DBI}^{(Φ,g,B)}$ with respect to $(φ,\nabla)$. The equations of motion that govern the dynamics of D-branes then follow. A complete action for a D-brane world-volume must include also the Chern-Simons/Wess-Zumino term $S_{CS/WZ}^{(C)}(φ,\nabla)$ that governs how the D-brane world-volume couples with the Ramond-Ramond fields $C$ on $Y$. In the current notes, a version $S^{(C,B)}_{CS/WZ}(φ,\nabla)$ of non-Abelian Chern-Simons/Wess-Zumino action functional for $(φ,\nabla)$ that follows the same guide with which we construct $S^{(Φ,g,B)}_{DBI}(φ,\nabla)$ is constructed for lower-dimensional D-branes (i.e. D(-1)-, D0-, D1-, D2-branes). Its first variation $δS^{(C,B)}_{CS/WZ}(φ,\nabla)/δ(φ,\nabla)$ is derived and its contribution to the equations of motion for $(φ, \nabla)$ follows. The current notes lay down a foundation toward the dynamics of D-branes along the line of this D-project.

hep-th↗