Showing papers in "Crelle's Journal in 2009"

Deformation theory of representations of prop(erad)s II

Abstract: In this paper and its follow-up [Merkulov and Vallette, J. reine angew. Math.], we study the deformation theory of morphisms of properads and props thereby extending Quillen's deformation theory for commutative rings to a non-linear framework. The associated chain complex is endowed with an L∞-algebra structure. Its Maurer-Cartan elements correspond to deformed structures, which allows us to give a geometric interpretation of these results. To do so, we endow the category of prop(erad)s with a model category structure. We provide a complete study of models for prop(erad)s. A new effective method to make minimal models explicit, that extends the Koszul duality theory, is introduced and the associated notion is called homotopy Koszul. As a corollary, we obtain the (co)homology theories of (al)gebras over a prop(erad) and of homotopy (al)gebras as well. Their underlying chain complex is endowed with an L∞-algebra structure in general and a Lie algebra structure only in the Koszul case. In particular, we make the deformation complex of morphisms from the properad of associative bialgebras explicit. For any minimal model of this properad, the boundary map of this chain complex is shown to be the one defined by Gerstenhaber and Schack. As a corollary, this paper provides a complete proof of the existence of an L∞-algebra structure on the Gerstenhaber-Schack bicomplex associated to the deformations of associative bialgebras.

Deformation theory of representation of prop(erad)s I

Abstract: In this paper and its follow-up, we study the deformation theory of morphisms of properads and props thereby extending Quillen's deformation theory for commutative rings to a non-linear framework. The associated chain complex is endowed with an L_infinity-algebra structure. Its Maurer-Cartan elements correspond to deformed structures, which allows us to give a geometric interpretation of these results. To do so, we endow the category of prop(erad)s with a model category structure. We provide a complete study of models for prop(erad)s. A new effective method to make minimal models explicit, that extends the Koszul duality theory, is introduced and the associated notion is called homotopy Koszul. As a corollary, we obtain the (co)homology theories of (al)gebras over a prop(erad) and of homotopy (al)gebras as well. Their underlying chain complex is endowed with an L_infinity-algebra structure in general and a Lie algebra structure only in the Koszul case. In particular, we make the deformation complex of morphisms from the properad of associative bialgebras explicit. For any minimal model of this properad, the boundary map of this chain complex is shown to be the one defined by Gerstenhaber and Schack. As a corollary, this paper provides a complete proof of the existence of an L_infinity-algebra structure on the Gerstenhaber-Schack bicomplex associated to the deformations of associative bialgebras.

The holonomy groupoid of a singular foliation

Abstract: We construct the holonomy groupoid of any singular foliation. In the regular case this groupoid coincides with the usual holonomy groupoid of Winkelnkemper ([H. E. Winkelnkemper, The graph of a foliation, Ann. Glob. Anal. Geom. 1 (3) (1983), 51–75.]); the same holds in the singular cases of [J. Pradines, How to define the differentiable graph of a singular foliation, C. Top. Geom. Diff. Cat. XXVI(4) (1985), 339–381.], [B. Bigonnet, J. Pradines, Graphe d'un feuilletage singulier, C. R. Acad. Sci. Paris 300 (13) (1985), 439–442.], [C. Debord, Local integration of Lie algebroids, Banach Center Publ. 54 (2001), 21–33.], [C. Debord, Holonomy groupoids of singular foliations, J. Diff. Geom. 58 (2001), 467–500.], which from our point of view can be thought of as being “almost regular”. In the general case, the holonomy groupoid can be quite an ill behaved geometric object. On the other hand it often has a nice longitudinal smooth structure. Nonetheless, we use this groupoid to generalize to the singular case Connes' construction of the C*-algebra of the foliation. We also outline the construction of a longitudinal pseudo-differential calculus; the analytic index of a longitudinally elliptic operator takes place in the K-theory of our C*-algebra. In our construction, the key notion is that of a bi-submersion which plays the role of a local Lie groupoid defining the foliation. Our groupoid is the quotient of germs of these bi-submersions with respect to an appropriate equivalence relation.

Heat kernel upper bounds for jump processes and the first exit time

Abstract: for all t > 0, x ∈ M , and f ∈ L2(M,μ). The function pt(x, y) can be considered as the transition density of the associated Markov processX = {Xt}t≥0, and the question of estimating of pt(x, y), which is the main subject of this paper, is closely related to the properties of X. The function pt(x, y) is also referred to as a heat kernel, and this terminology goes back to the classical Gauss-Weierstrass heat kernel associated with the heat semigroup {e}t≥0 in R n, whose Markov process is Brownian motion. A somewhat more general but still well treated case is when (M,d, μ) is a Riemannian metric measure space, that is, M is a Riemannian manifold,

A singular energy minimizing free boundary

Abstract: Abstract We consider the problem of minimizing the energy functional ∫(|∇u|2 + χ {u>0}). We show that the singular axissymmetric critical point of the functional is an energy minimizer in dimension 7. This is the first example of a non-smooth energy minimizer. It is analogous to the Simons cone, a least area hypersurface in dimension 8.

A finiteness theorem for canonical heights attached to rational maps over function fields

Abstract: Let K be a function field, let φ ∈ K(T ) be a rational map of degree d ≥ 2 defined over K, and suppose that φ is not isotrivial. In this paper, we show that a point P ∈ P(K) has φ-canonical height zero if and only if P is preperiodic for φ. This answers affirmatively a question of Szpiro and Tucker, and generalizes a recent result of Benedetto from polynomials to rational functions. We actually prove the following stronger result, which is a variant of the Northcott finiteness principle: there exists e > 0 such that the set of points P ∈ P(K) with φ-canonical height at most e is finite. Our proof is essentially analytic, making use of potential theory on Berkovich spaces to study the dynamical Green’s functions gφ,v(x, y) attached to φ at each place v of K. For example, we show that every conjugate of φ has bad reduction at v if and only if gφ,v(x, x) > 0 for all x ∈ P1Berk,v, where P 1 Berk,v denotes the Berkovich projective line over the completion of Kv. In an appendix, we use a similar method to give a new proof of the Mordell-Weil theorem for elliptic curves over K.

C*-algebras and self-similar groups

Abstract: Abstract We study Cuntz-Pimsner algebras naturally associated with self-similar groups (like iterated monodromy groups of expanding dynamical systems). In particular, we show how to reconstruct the Julia set of an expanding map from the Cuntz-Pimsner algebra of the associated iterated monodromy group and the gauge action on it. We compute K-theory of algebras associated with complex hyperbolic rational functions. It is proved that under some natural conditions the Cuntz-Pimsner algebra of a self-similar group is purely infinite, simple and nuclear. We also show a relation of our algebras with Ruelle algebras of the associated solenoids.

Gröbner geometry of vertex decompositions and of flagged tableaux

Abstract: We relate a classic algebro-geometric degeneration technique, dating at least to (Hodge 1941), to the notion of vertex decompositions of simplicial com- plexes. The good case is when the degeneration is reduced, and we call this a geometric vertex decomposition. Our main example in this paper is the family of vexillary matrix Schubert vari- eties, whose ideals are also known as (one-sided) ladder determinantal ideals. Us- ing a diagonal term order to specify the (Grobner) degeneration, we show that these have geometric vertex decompositions into simpler varieties of the same type. From this, together with the combinatorics of the pipe dreams of (Fomin- Kirillov 1996), we derive a new formula for the numerators of their multigraded Hilbert series, the double Grothendieck polynomials, in terms of flagged set-valued tableaux. This unifies work of (Wachs 1985) on flagged tableaux, and (Buch 2002) on set-valued tableaux, giving geometric meaning to both. This work focuses on diagonal term orders, giving results complementary to those of (Knutson-Miller 2004), where it was shown that the generating minors form a Grobner basis for any antidiagonal term order and any matrix Schubert va- riety. We show here that under a diagonal term order, the only matrix Schubert varieties for which these minors form Grobner bases are the vexillary ones, reach- ing an end toward which the ladder determinantal literature had been building. CONTENTS

Quantum groups acting on 4 points

Abstract: We classify the compact quantum groups acting on 4 points. These are the quantum subgroups of the quantum permutation group Q4. Our main tool is a new presentation for the algebra C(Q4), corresponding to an isomorphism of type Q4 ≃ SO 1(3). The quantum subgroups of Q4 are subject to a McKay type correspondence, that we describe at the level of algebraic invariants.

Cones over pseudo-Riemannian manifolds and their holonomy

Abstract: By a classical theorem of Gallot (1979), a Riemannian cone over a complete Riemannian manifold is either flat or has irreducible holonomy. We consider metric cones with reducible holonomy over pseudo-Riemannian manifolds. First we describe the local structure of the base of the cone when the holonomy of the cone is decomposable. For instance, we find that the holonomy algebra of the base is always the full pseudo-orthogonal Lie algebra. One of the global results is that a cone over a compact and complete pseudo-Riemannian manifold is either flat or has indecomposable holonomy. Then we analyse the case when the cone has indecomposable but reducible holonomy, which means that it admits a parallel isotropic distribution. This analysis is carried out, first in the case where the cone admits two complementary distributions and, second for Lorentzian cones. We show that the first case occurs precisely when the local geometry of the base manifold is para-Sasakian and that of the cone

Multiplication operators on the Bergman space via the Hardy space of the bidisk

Abstract: In this paper, we develop a machinery to study multiplication operators on the Bergman space via the Hardy space of the bidisk. We show that only a multiplication operator by a finite Blaschke product has a unique reducing subspace on which its restriction is unitarily equivalent to the Bergman shift. Using the machinery we study the structure of reducing subspaces unitary equivalence of a multiplication operator on the Bergman space. As a consequence, we completely classify reducing subspaces of the multiplication operator by a Blaschke product φ with order three on the Bergman space to solve a conjecture of Zhu [38] and obtain that the number of minimal reducing subspaces of the multiplication operator equals the number of connected components of the Riemann surface of φ−1 ◦ φ over D.

Borcherds forms and generalizations of singular moduli

Abstract: We give a factorization of averages of Borcherds forms over CM points associated to a quadratic form of signature (n,2). As a consequence of this result, we are able to state a theorem like that of Gross and Zagier about which primes can occur in this factorization. One remarkable phenomenon we observe is that the regularized theta lift of a weakly holomorphic modular form is always finite.

ℒ-optimal transportation for Ricci flow

Abstract: We introduce the notion of L-optimal transportation, and use it to construct a natural monotonic quantity for Ricci flow which includes a selection of other monotonicity results, including some key discoveries of Perelman [13] (both related to entropy and to L-length) and a recent result of McCann and the author [11].

Arithmetic duality theorems for 1-motives

Abstract: We prove several duality theorems for the Galois and etale cohomology of 1-motives defined over local and global fields and establish a 12-term Poitou-Tate type exact sequence. The results give a common generalisation and sharpening of well-known theorems by Tate on abelian varieties as well as results by Tate/Nakayama and Kottwitz on algebraic tori.

Twisted conjugacy classes in nilpotent groups

Abstract: A group is said to have the $R_\infty$ property if every automorphism has an infinite number of twisted conjugacy classes. We study the question whether $G$ has the $R_\infty$ property when $G$ is a finitely generated torsion-free nilpotent group. As a consequence, we show that for every positive integer $n\ge 5$, there is a compact nilmanifold of dimension $n$ on which every homeomorphism is isotopic to a fixed point free homeomorphism. As a by-product, we give a purely group theoretic proof that the free group on two generators has the $R_\infty$ property. The $R_{\infty}$ property for virtually abelian and for $\mathcal C$-nilpotent groups are also discussed.

Cohomological finiteness conditions for elementary amenable groups

Abstract: It is proved that every elementary amenable group of type FP? admits a cocompact classifying space for proper actions

Le foncteur des invariants sous l'action du pro-p-Iwahori de GL2(F)

Abstract: Abstract Let F be a p-adic field with uniformizer π. Given a smooth mod p-representation of G = GL2(F)/π, we consider its subspace of invariants under the action of the pro-p-Iwahori subgroup and get this way a functor taking values in the category of right modules over the pro-p-Hecke algebra with characteristic p. We show that if F = ℚ p , this functor restricted to the representations generated by their pro-p-invariants is an equivalence of categories, and give examples of other p-adic fields for which it is not the case.

Groupoids and an index theorem for conical pseudo-manifolds

Abstract: We define an analytical index map and a topological index map for conical pseudomanifolds. These constructions generalize the analogous constructions used by Atiyah and Singer in the proof of their topological index theorem for a smooth, compact manifold $M$. A main ingredient is a non-commutative algebra that plays in our setting the role of $C_0(T^*M)$. We prove a Thom isomorphism between non-commutative algebras which gives a new example of wrong way functoriality in $K$-theory. We then give a new proof of the Atiyah-Singer index theorem using deformation groupoids and show how it generalizes to conical pseudomanifolds. We thus prove a topological index theorem for conical pseudomanifolds.

Complex analytic geometry and analytic-geometric categories

Abstract: Abstract The notion of an analytic-geometric category was introduced by v. d. Dries and Miller in [Lou van den Dries and Chris Miller, Geometric categories and o-minimal structures, Duke Math. J. 84 (1996), no. 2, 497–540.]. It is a category of subsets of real analytic manifolds which extends the category of subanalytic sets. This paper discusses connections between the subanalytic category, or more generally analytic-geometric categories, and complex analytic geometry. The questions are of the following nature: We start with a subset A of a complex analytic manifold M and assume that A is an object of an analytic-geometric category (by viewing M as a real analytic manifold of double dimension). We then formulate conditions under which A, its closure or its image under a holomorphic map is a complex analytic set. In the second part of the paper we consider the notion of a complex -manifold, which generalizes that of a compact complex manifold. We discuss uniformity in parameters, in this context, within families of complex manifolds and their high-order holomorphic tangent bundles. We then prove a result on uniform embeddings of analytic subsets of -manifolds into a projective space, which extends theorems of Campana ([F. Campana, Algébricité et compacité dans l'espace des cycles d'un espace analytique complexe, Math. Ann. 251 (1980), no. 1, 7–18.]) and Fujiki ([Akira Fujiki, On the Douady space of a compact complex space in the category 𝒞, Nagoya Math. J. 85 (1982), 189–211.]) on compact complex manifolds.

Unbounded Fredholm modules and double operator integrals

Abstract: In noncommutative geometry one is interested in invariants such as the Fredholm index or spectral flow and their calculation using cyclic cocycles. A variety of formulae have been established under side conditions called summability constraints. These can be formulated in two ways, either for spectral triples or for bounded Fredholm modules. We study the relationship between these by proving various properties of the map on unbounded self adjoint operators $D$ given by $f(D)=D(1+D^2)^{-1/2}$. In particular we prove commutator estimates which are needed for the bounded case. In fact our methods work in the setting of semifinite noncommutative geometry where one has $D$ as an unbounded self adjoint linear operator affiliated with a semi-finite von Neumann algebra $\aM$. More precisely we show that for a pair $D,D_0$ of such operators with $D-D_0$ a bounded self-adjoint linear operator from $\aM$ and $ ({\bf 1}+D_0^2)^{-1/2}\in \sE$, where $\sE$ is a noncommutative symmetric space associated with $\aM$, then $$ \Vert f(D) - f (D_0) \Vert_{\sE} \leq C\cdot \Vert D-D_0\Vert_{\aM}. $$ This result is further used to show continuous differentiability of the mapping between an odd $\sE$-summable spectral triple and its bounded counterpart.

The Hartogs extension theorem on (n-1)-complete complex spaces

Abstract: Employing Morse theory for the global control of monodromy and the method of analytic discs for local extension, we establish a version of the global Hartogs extension theorem in a singular setting: for every domain D of an (n-1)-complete normal complex space X of pure dimension n >= 2 and for every compact set K in D such that D - K is connected, holomorphic or meromorphic functions in D - K extend holomorphically or meromorphically to D. Normality is an unvavoidable assumption for holomorphic extension, but we show that meromorphic extension holds on a reduced globally irreducible (not necessarily normal) X of pure dimension n >=2 provided that the regular part of D - K is connected.

Trees and mapping class groups

Abstract: There is a forgetful map from the mapping class group of a punctured surface to that of the surface with one fewer puncture. We prove that finitely generated purely pseudo-Anosov subgroups of the kernel of this map are convex cocompact in the sense of B. Farb and L. Mosher. In particular, we obtain an affirmative answer to their question of local convex cocompactness of K. Whittlesey's group. In the course of the proof, we obtain a new proof of a theorem of I. Kra. We also relate the action of this kernel on the curve complex to a family of actions on trees. This quickly yields a new proof of a theorem of J. Harer.

Rational points on quartic hypersurfaces

Abstract: Let X be a projective non-singular quartic hypersurface of dimension 39 or more, which is defined over . We show that X() is non-empty provided that X() is non-empty and X has p-adic points for every prime p. © 2009 Walter de Gruyter.

Transition maps at non-resonant hyperbolic singularities are o-minimal

Abstract: We construct a model complete and o-minimal expansion of the field of real numbers such that, for any planar analytic vector field X and any isolated, non-resonant hyperbolic singularity p of X, a transition map for X at p is definable in this structure. This structure also defines all convergent generalized power series with natural support and is polynomially bounded.

A short proof of the λg -conjecture without Gromov-Witten theory: Hurwitz theory and the moduli of curves

Abstract: We give a short and direct proof of the λg-Conjecture. The approach is through the Ekedahl-Lando-Shapiro-Vainshtein theorem, which establishes the “polynomiality” of Hurwitz numbers, from which we pick off the lowest degree terms. The proof is independent of GromovWitten theory. We briefly describe the philosophy behind our general approach to intersection numbers and how it may be extended to other intersection number conjectures.

The moduli space of cubic threefolds via degenerations of the intermediate Jacobian

Abstract: A well known result of Clemens and Griffiths says that a smooth cubic threefold can be recovered from its intermediate Jacobian. In this paper we discuss the possible degenerations of these abelian varieties, and thus give a description of the compactification of the moduli space of cubic threefolds obtained in this way. The relation between this compactification and those constructed in the work of Allcock-Carlson-Toledo and Looijenga-Swierstra is also considered, and is similar in spirit to the relation between the various compactifications of the moduli spaces of low genus curves.

Cayley decompositions of lattice polytopes and upper bounds for h*-polynomials

Abstract: We give an effective upper bound on the h-polynomial of a lattice polytope in terms of its degree and leading coefficient, confirming a conjecture of Batyrev. We deduce this bound as a consequence of a strong Cayley decomposition theorem which says, roughly speaking, that any lattice polytope with a large multiple that has no interior lattice points has a nontrivial decomposition as a Cayley sum of polytopes of smaller dimension. Polytopes with nontrivial Cayley decompositions correspond to projectivized sums of toric line bundles, and our approach is partially inspired by classification results of Fujita and others in algebraic geometry. In an appendix, we interpret our Cayley decomposition theorem in terms of adjunction theory for toric varieties.

Domains of convergence for monomial expansions of holomorphic functions in infinitely many variables

Abstract: Abstract Let ℱ(R) be a set of holomorphic functions on a Reinhardt domain R in a Banach sequence space (as e.g. all holomorphic functions or all m-homogeneous polynomials on the open unit ball of ). We give a systematic study of the sets dom ℱ(R) of all z ∈ R for which the monomial expansion of every ƒ ∈ ℱ(R) converges. Our results are based on and improve the former work of Bohr, Dineen, Lempert, Matos and Ryan. In particular, we show that up to any ε > 0 is the unique Banach sequence space X for which the monomial expansion of each holomorphic function ƒ converges at each point of a given Reinhardt domain in X. Our study shows clearly why Hilbert's point of view to develop a theory of infinite dimensional complex analysis based on the concept of monomial expansion, had to be abandoned early in the development of the theory.