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Milena Pabiniak

Publications and source records attributed to Milena Pabiniak.

15 recordsLinked to original sources
arXiv2022

Generalizing the Mukai Conjecture to the symplectic category and the Kostant game

In this paper we pose the question of whether the (generalized) Mukai inequalities hold for compact, positive monotone symplectic manifolds. We first provide a method that enables one to check whether the (generalized) Mukai inequalities hold true. This only makes use of the almost complex structure of the manifold and the analysis of the zeros of the so-called generalized Hilbert polynomial, which takes into account the Atiyah-Singer indices of all possible line bundles. We apply this method to generalized flag varieties. In order to find the zeros of the corresponding generalized Hilbert polynomial we introduce a modified version of the Kostant game and study its combinatorial properties.

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arXiv2020

Givental's non-linear Maslov index on lens spaces

Givental's non-linear Maslov index, constructed in 1990, is a quasimorphism on the universal cover of the identity component of the contactomorphism group of real projective space. This invariant was used by several authors to prove contact rigidity phenomena such as orderability, unboundedness of the discriminant and oscillation metrics, and a contact geometric version of the Arnold conjecture. In this article we give an analogue for lens spaces of Givental's construction and its applications.

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arXiv2020

Symplectic cohomological rigidity via toric degnerations

In this paper we study whether symplectic toric manifolds are symplectically cohomologically rigid. Here we say that symplectic cohomological rigidity holds for some family of symplectic manifolds if the members of that family can be distinguished by their integral cohomology rings and the cohomology classes of their symplectic forms. We show how toric degenerations can be used to produce the symplectomorphisms necessary to answer this question. As a consequence we prove that symplectic cohomological rigidity holds for the family of symplectic Bott manifolds with rational symplectic form whose rational cohomology ring is isomorphic to $\mathrm{H}^*((\mathbb{CP}^1)^n;\mathbb{Q})$ for some $n$. In particular, we classify such manifolds up to symplectomorphism. Moreover, we prove that any symplectic toric manifold with rational symplectic form whose integral cohomology ring is isomorphic to $\mathrm{H}^*((\mathbb{CP}^1)^n;\mathbb{Z})$ is symplectomorphic to $(\mathbb{CP}^1)^n$ with a product symplectic structure.

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arXiv2018

Toric degenerations in symplectic geometry

A toric degeneration in algebraic geometry is a process where a given projective variety is being degenerated into a toric one. Then one can obtain information about the original variety via analyzing the toric one, which is a much easier object to study. Harada and Kaveh described how one incorporates a symplectic structure into this process, providing a very useful tool for solving certain problems in symplectic geometry. Below we present applications of this method to questions about the Gromov width, and cohomological rigidity problems.

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arXiv2017

The Gromov width of coadjoint orbits of the symplectic group

We prove that the Gromov width of coadjoint orbits of the symplectic group is at least equal to the upper bound known from the works of Zoghi and Caviedes. This establishes the actual Gromov width. Our work relies on a toric degeneration of a coadjoint orbit to a toric variety. The polytope associated to this toric variety is a string polytope arising from a string parametrization of elements of a crystal basis for a certain representation of the symplectic group.

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arXiv2017

On the Gromov width of polygon spaces

For generic $r=(r_1,\ldots,r_n) \in \mathbb{R}^n_+$ the space $\mathcal{M}(r)$ of $n$--gons in $\mathbb{R}^3$ with edges of lengths $r$ is a smooth, symplectic manifold. We investigate its Gromov width and prove that the expression $$2π\min \{2 r_j, (\sum_{i \neq j} r_i) - r_j\,\,|\, j=1,\ldots,n\}$$ is the Gromov width of all (smooth) $5$--gon spaces and of $6$--gon spaces, under some condition on $r \in \mathbb{R}^6_+$. The same formula constitutes a lower bound for all (smooth) spaces of $6$--gons. Moreover, we prove that the Gromov width of $\mathcal{M}(r)$ is given by the above expression when $\mathcal{M}(r)$ is symplectomorphic to $\mathbb{C}\mathbb{P}^{n-3}$, for any $n \geq 4$.

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arXiv2016

On displaceability of pre-Lagrangian fibers in contact toric manifolds

In this note we analyze displaceability of pre-Lagrangian toric fibers in contact toric manifolds. While every symplectic toric manifold contains at least one non-displaceable Lagrangian toric fiber and infinitely many displaceable ones, we show that this is not the case for contact toric manifolds. More precisely, we prove that for the contact toric manifolds $\mathbb{S}^{2d-1} (d\geq 2)$ and $\mathbb{T}^k \times \mathbb{S}^{2d+k-1} (d \geq 1)$ all pre-Lagrangian toric fibers are displaceable, and that for all contact toric manifolds for which the toric action is free, except possibly non-trivial $\mathbb{T}^3$-bundles over $\mathbb{S}^2$, all pre-Lagrangian toric fibers are non-displaceable. Moreover we also prove that if for a compact connected contact toric manifold all but finitely many pre-Lagrangian toric fibers are non-displaceable then the action is necessarily free. On the other hand, as we will discuss, displaceability of all pre-Lagrangian toric fibers seems to be related to the non-orderability of the underlying contact manifolds.

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arXiv2015

Every symplectic toric orbifold is a centered reduction of a Cartesian product of weighted projective spaces

We prove that every symplectic toric orbifold is a centered reduction of a Cartesian product of weighted projective spaces. A theorem of Abreu and Macarini shows that if the level set of the reduction passes through a non-displaceable set then the image of this set in the reduced space is also non-displaceable. Using this result we show that every symplectic toric orbifold contains a non-displaceable fiber and we identify this fiber.

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arXiv2015

Canonical bases for the equivariant cohomology and K-theory rings of symplectic toric manifolds

Let $M$ be a symplectic toric manifold acted on by a torus $\mathbb{T}$. In this work we exhibit an explicit basis for the equivariant K-theory ring $\mathcal{K}_{\mathbb{T}}(M)$ which is canonically associated to a generic component of the moment map. We provide a combinatorial algorithm for computing the restrictions of the elements of this basis to the fixed point set; these, in turn, determine the ring structure of $\mathcal{K}_{\mathbb{T}}(M)$. The construction is based on the notion of local index at a fixed point, similar to that introduced by Guillemin and Kogan in [GK]. We apply the same techniques to exhibit an explicit basis for the equivariant cohomology ring $H_{\mathbb{T}}(M; \mathbb{Z})$ which is canonically associated to a generic component of the moment map. Moreover we prove that the elements of this basis coincide with some well-known sets of classes: the equivariant Poincaré duals to the closures of unstable manifolds, and also the canonical classes introduced by Goldin and Tolman in [GT], which exist whenever the moment map is index increasing.

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arXiv2013

Gromov width of non-regular coadjoint orbits of U(n), SO(2n) and SO(2n+1)

Let G be a compact connected Lie group G and T its maximal torus. The coadjoint orbit O_lambda through lambda in Lie(T)^* is canonically a symplectic manifold. Therefore we can ask the question about its Gromov width. In many known cases the Gromov width is exactly the minimum over the set {< alpha_j^{\vee},lambda > ; alpha_j^{\vee} a coroot and < alpha_j^{\vee},lambda > positive}. We show that the Gromov width of coadjoint orbits of the unitary group and of most of the coadjoint orbits of the special orthogonal group is at least the above minimum. The proof uses the torus action coming from the Gelfand-Tsetlin system.

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arXiv2013

Localization and Specialization for Hamiltonian Torus Actions

We consider a Hamiltonian action of n-dimensional torus, T^n, on a compact symplectic manifold (M,ω) with d isolated fixed points. For every fixed point p there exists (though not unique) a class a_p in H^*_{T}(M; Q) such that the collection {a_p}, over all fixed points, forms a basis for H^*_{T}(M; Q) as an H^*(BT; Q) module. The map induced by the inclusion, ι^*:H^*_{T}(M; Q) \rightarrow H^*_{T}(M^{T}; Q)= \oplus_{j=1}^{d}Q[x_1, ..., x_n] is injective. We use such classes {a_p} to give necessary and sufficient conditions for f=(f_1, ...,f_d) in \oplus_{j=1}^{d}Q[x_1, ..., x_n] to be in the image of ι^*, i.e. to represent an equiviariant cohomology class on M. In the case when T is a circle and present these conditions explicitly. We explain how to combine this 1-dimensional solution with Chang-Skjelbred Lemma in order to obtain the result for a torus T of any dimension. Moreover, for a GKM T-manifold M our techniques give combinatorial description of H^*_{K}(M; Q), for a generic subgroup K \hookrightarrow T, even if M is not a GKM K-manifold.

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arXiv2012

Displacing Lagrangians in the manifolds of full flags in C^3

In symplectic geometry a question of great importance is whether a (Lagrangian) submanifold is displaceable, that is, if it can be made disjoint from itself by the means of a Hamiltonian isotopy. In these notes we analyze the coadjoint orbits of SU(n) and their Lagrangian submanifolds that are fibers of the Gelfand-Tsetlin map. We use the coadjoint action to displace a large collection of these fibers. Then we concentrate on the case n=3 and apply McDuff's method of probes to show that "most" of the generic Gelfand-Tsetlin fibers are displaceable. "Most" means "all but one" in the non-monotone case, and means "all but a 1-parameter family" in the monotone case. In the case of non-monotone manifold of full flags we present explicitly an unique non-displaceable Lagrangian fiber (S^1)^3. This fiber was already proved to be non-displaceable in \cite{NNU}. Our contribution is in displacing other fibers and thus proving the uniqueness.

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arXiv2011

Lower bounds for Gromov width in the SO(n) coadjoint orbits

Let G be a compact connected Lie group G and T its maximal torus. The coadjoint orbit O_λ through λin the dual of the Lie algebra of T, is canonically a symplectic manifold. Therefore we can ask the question of its Gromov width. In many known cases the width is exactly the minimum over the positive results of pairing λwith coroots: min{< α_j^{\vee},λ> ; α_j^{\vee} is a coroot and < α_j^{\vee},λ> is positive}. We will show that the Gromov width for regular coadjoint orbits of the special orthogonal group is at least this minimum. The proof uses the torus action coming from the Gelfand-Tsetlin system.

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arXiv2011

Lower bounds for Gromov width of coadjoint orbits in U(n)

We use the Gelfand-Tsetlin pattern to construct an effective Hamiltonian, completely integrable action of a torus T on an open dense subset of a coadjoint orbit of the unitary group. We then identify a proper Hamiltonian T-manifold centered around a point in the dual of the Lie algebra of T. A theorem of Karshon and Tolman says that such a manifold is equivariantly symplectomorphic to a particular subset of R^2D. This fact enables us to construct symplectic embeddings of balls into certain coadjoint orbits of the unitary group, and therefore obtain a lower bound for their Gromov width. Using the identification of the dual of the Lie algebra of the unitary group with the space of (n x n) Hermitian matrices, the main theorem states that for a coadjoint orbit through λ=diag(λ_1, ..., λ_n) in the dual of the Lie algebra of the unitary group, where at most one eigenvalue is repeated, the lower bound for Gromov width is equal to the minimum of the differences λ_i-λ_j, over all λ_i>λ_j. For a generic orbit (i.e. with distinct λ_i's), with additional integrality conditions, this minimum has been proved to be exactly the Gromov width of the orbit. For nongeneric orbits this lower bound is new.

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