arXiv subjects
Publications and source records attributed to Federico Quallbrunn.
We determine the structure of the singular locus of generic codimension-$q$ logarithmic foliations and its relation with the unfoldings of said foliations. In the case where the ambient variety is the projective space $\mathbb{P}^n$ we calculate the graded ideal defining the scheme of persistent singularities.
We show a stability-type theorem for foliations on projective spaces which arise as pullbacks of foliations with a split tangent sheaf on weighted projective spaces. As a consequence, we will be able to construct many irreducible components of the corresponding spaces of foliations, most of them being previously unknown. This result also provides an alternative and unified proof for the stability of other families of foliations.
In this paper, we investigate families of singular holomorphic Lie algebroids on complex analytic spaces. We introduce and study a special type of deformation called unfoldings of Lie algebroids, which generalizes the theory of singular holomorphic foliations developed by T. Suwa. We show that a one to one correspondence between transversal unfoldings and holomorphic flat connections on a natural Lie algebroid on the bases exists.
Let $ω$ be a differential $q$-form defining a foliation of codimension $q$ in a projective variety. In this article we study the singular locus of $ω$ in various settings. We relate a certain type of singularities, which we name \emph{persistent}, with the unfoldings of $ω$, generalizing previous work done on foliations of codimension $1$ in projective space. We also relate the absence of persistent singularities with the existence of a connection in the sheaf of $1$-forms defining the foliation. In the latter parts of the article we extend some of these results to toric varieties by making computations on the Cox ring and modules over this ring.
We work with codimension one foliations in the projective space $\mathbb{P}^{n}$, given a differential one form $ω\in H^0(\mathbb{P}^n,Ω^1_{\mathbb{P}^n}(e))$, such differential form verifies the Frobenius integrability condition $ω\wedge dω=0$. In this work we show that the Camacho-Lins Neto regularity, applied for $ω$, is equivalent to the fact that every first order unfolding of $ω$ is trivial up to isomorphism. We do this by computing the Castelnuovo-Mumford regularity of the ideal $I(ω)$ of first order unfoldings. With this result, we are also showing that the only regular projective foliations, with reduced singular locus, are the ones that have singular locus only Kupka type singularities. At last we use these results to show that every foliation $\varpi\in Ω^1_{\mathbb{C}^{n+1}}$, with initial form $ω$ regular and dicritical, is isomorphic to $ω$.
We will work with codimension one holomorphic foliations over the complex projective space, represented by integrable forms $ω\in H^0(Ω^1_{\PP^n}(e))$. Our main result is that, under suitable hypotheses, the Kupka set of the singular locus of $ω\in H^0(Ω^1_{\PP^3}(e))$, defined algebraically as a scheme, turns out to be arithmetically Cohen-Macaulay. As a consequence, we prove the connectedness of the Kupka set in $\PP^n$, and the splitting of the tangent sheaf of the foliation, provided that it is locally free.
Let $ω$ be a differential 1-form defining an algebraic foliation of codimension 1 in projective space. In this article we use commutative algebra to study the singular locus of $ω$ through its ideal of definition. Then, we expose the relation between the ideal defining the Kupka components of the singular set of $ω$ and the first order unfoldings of $ω$. Exploiting this relation, we show that the set of Kupka points of $ω$ is generically not empty. As an application of this results, we can compute the ideal of first order unfoldings for some known components of the space of foliations.
Following T. Suwa, we study unfoldings of algebraic foliations and their relationship with families of foliations, making focus on those unfoldings related to trivial families. The results obtained in the study of unfoldings are then applied to obtain information on the structure of foliations on projective spaces.
A singular distribution on a non-singular variety $X$ can be defined either by a subsheaf $D$ of the tangent sheaf, or by the zeros of a subsheaf $D^0$ of the sheaf of 1-forms. Although both definitions are equivalent under mild conditions on $D$, they give rise, in general, to non-equivalent notions of flat families. In this work we investigate conditions under which both notions of flat families are equivalent. In the last sections we focus on the case where the distribution is integrable, and we use our results to generalize a theorem of Cukierman and Pereira.