Il seminario riunisce i gruppi di geometria e algebra di UNIBA e POLIBA. La cadenza del seminario è mensile ad eccezione di eventuali contributi di ospiti esterni. Per ricevere aggiornamenti o informazioni scrivere a Sara Azzali, Lucio Centrone o Francesco Pavese.
[Seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
Swanhild Bernstein (TU Bergakademie Freiberg)
Q^2 Clifford algebras
[Seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
Martha Lina Zimmerman (TU Bergakademie Freiberg)
Jackson Clifford Analysis and the q-Fock spaces
Seminari Passati
Marian Ioan Munteanu (Alexandru Ioan Cuza University of Iasi, Romania)
Magnetic curves in contact geometry
Dynamical systems on 3-manifolds have been paid much attention along the time. In particular, magnetic trajectories are solutions of a second order differential equation (known as the Lorentz equation) and they generalise geodesics. A magnetic field on a Riemannian manifold is defined
by a closed 2-form that helps, together with the metric, to define the Lorentz force. On the other hand, magnetic curves derive from the variational problem of the Landau-Hall functional, which is, in the absence of a magnetic field, nothing but the kinetic energy functional.
The dimension 3 is rather special, since it allows us to identify 2-forms with vector fields via the Hodge ⋆ operator and the volume form of the (oriented) manifold. Moreover, in dimension 3, one may define a cross product and therefore, the Lorentz equation may be written in an easier way.
The challenge is to solve the differential equation in order to find an explicit solution, meaning the explicit parametrization for the magnetic trajectories. Nevertheless, this is not always possible and, because of that, it is necessary to understand the behaviour of the solution.
Recent studies are done in 3-dimensional Sasakian manifolds, where the contact 2-form naturally defines a magnetic field. The solutions of the Lorentz equation, usually called contact magnetic trajectories, are often expressed in a concrete parametrization. It can be proved a reduction
result for the codimension in a Sasakian space form, that is, essentially, we can reduce the study (of a magnetic curve in a Sasakian space form) to dimension 3. The geometry of magnetic trajectories have been recently studied in the 3-sphere, in the Berger 3-sphere, in the Heisenberg group Nil3 and in SL(2,R), respectively.
Another important problem is the existence of closed curves which is a fascinating topic in dynamical systems. Periodic orbits of the contact magnetic fields on the unit 3-sphere and in the Berger 3-sphere were found in the last two decades and conditions for the periodicity have been
obtained. A similar result has been recently given; it was proved that periodic contact magnetic curves in SL(2,R) can be quantized in the set of rational numbers.
The geometry of contact magnetic curves in SL(2,R) is much more beautiful. More precisely, it can be shown that every contact magnetic trajectory (of charge q) starting at the origin of SL(2,R) with initial velocity X and with charge q is the product of the homogeneous geodesic with initial
velocity X and the charged Reeb flow exp(2qs\xi). Similar results are obtained for the Berger spheres as well.
This talk is based on several papers, mainly in collaboration with Prof. Jun-ichi Inoguchi (Japan)
Homare Tadano (Yamaguchi University)
Bonnet--Myers type theorems for Sasaki--Ricci solitons
One of the most fundamental topics in Riemannian geometry is to investigate the relation between topology and geometric structure on Riemannian manifolds. A Sasaki-Ricci soliton is a generalization of a Sasaki-Einstein manifold, and plays an important role in the study of the Sasaki-Ricci flow. In this talk, we give several new Bonnet-Myers type theorems for complete Sasaki-Ricci solitons. These theorems not only extend Bonnet-Myers type theorems for complete Ricci solitons due to M. Fernandez-Lopez & E. Garcia-Rio (Math. Ann. 38 (2008), 893-896) and M. Limoncu (Math. Z. 271 (2012), 715-722), but also generalize the Bonnet-Myers type theorems for complete Sasaki manifolds due to I. Hasegawa & M. Seino (J. Hokkaido Univ. Education 32 (1981), 1-7) and Y. Nitta (Ann. Sc. Norm. Super. Pisa Cl. Sci. (5) 13 (2014), 207–224).
Giulio Binosi (Università di Firenze)
Dunkl approach to slice regular functions
[Seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
In this talk, we establish a connection between Dunkl analysis and slice analysis in the setting of Clifford algebras. Specifically, we show that a Clifford algebra-valued function is slice if, and only if, it belongs to the kernel of the Dunkl-spherical Dirac operator and that a slice function is slice regular if, and only if, it lies in the kernel of the Dunkl-Cauchy-Riemann operator for a suitable parameter. Based on this correspondence and the inverse Dunkl intertwining operator, we propose a new method to construct a family of classical monogenic functions from a given holomorphic function, in the spirit of Fueter’s theorem.
Calum Spicer (King's college London)
Moduli of Foliations
[Seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
I will explain some joint work in progress with R. Svaldi and S. Velazquez on the construction of moduli spaces of foliations which is modeled on the approach to the construction of the moduli space of curves. Time permitting I will explain some applications of this work to moduli problems of related structures (such as fibrations).
Francesco Esposito (Università della Basilicata)
An Introduction to Cauchy-Riemann Geometry
[Seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
This talk offers an introductory exploration of Cauchy-Riemann Geometry (or CR geometry), a mathematical area bridging Differential Geometry, Complex Analysis and Partial Differential Equations theory. Starting from the so-called tangential Cauchy-Riemann equations, we will introduce the foundational concepts of CR structures, which are particular complex subbundles on real manifolds.
We will then focus on the interplay between CR geometry and other branches of Differential Geometry such as contact, Sub-Riemannian and Lorentzian geometries.
Finally we will consider the counterpart of harmonic maps within the CR category, namely subelliptic harmonic maps. The principal part of the Euler-Lagrange equations system describing these maps is the sublaplacian, a second order elliptic degenerate yet subelliptic operator: this will bring into the picture the relevance of subelliptic PDEs, which play within CR geometry the same strong role held by elliptic theory in the Riemannian one.
Some of the results presented in this last section are part of a joint work with S. Dragomir and E. Loubeau.
Henrik Winther (The Arctic University of Norway)
Quaternion skew-Hermitian geometry
We consider the geometry of manifolds equipped with quaternion- or hypercomplex skew-Hermitian structures. These structures can be seen as either real manifolds equipped with a certain kind of quaternion-valued 2-forms, or as almost quaternionic manifolds equipped with compatible almost symplectic forms. We consider their first order integrability conditions, and in particular, we show that the torsion modules of these geometries contain equivalent summands, which in principle allows for multiple in-equivalent normalization conditions. This leads us to construct explicit canonical connections, and we develop a uniform normalization condition which realize these connections as minimal, hence giving rise to first order differential invariants. We also give interpretations of these invariants in terms of the underlying structures. Joint work with I. Chrysikos and J. Gregorovic.
Jose Seade
Universidad Nacional Autónoma de México
Visiting Professor UniBa
Indices and Residues of Holomorphic Foliations
The classical theorem of Poincaré-Hopf about the index of vector fields on smooth manifolds has given rise to a vast literature concerning indices of vector fields and Baum-Bott residues for singular holomorphic foliations. In this talk we will review some of the foundational aspects of this theory having as a spear-
head the GSV-index, an invariant that generalizes the Poincaré-Hopf index to the case of singular varietes.
Massimiliano Sala (Università di Trento)
On the cubic case of the big APN problem
APN functions are vectorial Boolean functions that play a fundamental role in providing security to block ciphers. The ideal APN functions would be permutations defined over binary vector spaces of even dimension. While there are many examples of odd-dimension APN permutations, only one (up to equivalence) even-dimensional APN permutation is known. Let us call "a good function" an even-dimensional APN permutation. The so-called "big APN problem" consists in finding good functions (or proving their non-existence). We will review known negative results, including the non-existence of good functions with quadratic or linear components. Due to these previous results, the next case to handle is the cubic case, that is, a good function where all components are cubics (their degree is three). We will present our theoretical advances towards the non-existence of such functions. This is joint work with Augustine Musukwa (Mzuzu University).
Plamen Koshlukov (Universidade Estadual de
Campinas)
Group gradings on solvable Lie algebras
Let $UT_n^{(-)}$ be the Lie algebra of the $n\times n$ upper triangular matrices over a field. The description of the group gradings on this álgebra is an important problem. When considering the associative algebra $UT_n$, it was shown by Valenti and Zaicev that every grading is isomorphic to elementar one (in other words all matrices $e_{ij}$ are homogeneous in the grading). The elementary gradings on $UT_n$ were described some 20 years ago by Di Vincenzo, PK, Valenti. Surprisingly (or not so) in the case of Lie algebras there appear gradings that are not isomorphic to elementary ones. We classify all group gradings on $UT_n^{(-)}$. Similar methods and results hold for the Jordan algebra $UT_n^{(+)}$. We also draw conclusions concerning the graded polynomial identities these gradings satisfy. This is a joint work with F. Yukihide, parts of it published around 2018, and also recently, in 2023, in streamlined and more general form.
Gian Pietro Pirola (Università di Pavia)
Sezioni del fibrato Jacobiano di curve piane e applicazioni
[Seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
Studiamo le funzioni normali (sezioni del fibrato Jacobiano) definite sullo spazio dei moduli di curve piane (puntate).
Utilizzando tecniche introdotte da Griffiths Green e Voisin dimostriamo che una funzione normale con supporto non banale ma sufficientemente "piccolo", non può essere "localmente costante".
Come applicazione, diamo una dimostrazione variazionale del seguente teorema di Zu:
Teorema: Se C è una curva piana molto generale di grado d e C' è una qualsiasi curva di grado d', allora la cardinalità i(C,C') dell'intersezione tra C e C' è >d-3.
Mostriamo inoltre che se d>3 e i(C,C')=d-2 allora C' è una retta bitangente o di flesso. Per d=4 questo è un risultato di Chen Rield e Yeong.
Il lavoro e' frutto di una collaborazione con Lorenzo Fassina.
Ana Cristina Ferreira (CMAT University of Minho, Portugal) Visiting Professor UniBa
Dynamics and completeness of the geodesic flow on pseudo and holomorphic Riemannian manifolds
We will present a self-contained overview on the geometry of the geodesic flow of Lie groups with left-invariant pseudo-Riemannian or holomorphic-Riemannian metrics. As well as recalling some beautiful and seminal classical theory, we will present some recent developments in this topic. This talk will be based on a series of joint works with S. Chaib, A. Elshafei, H.Reis, M. Sanchez and A. Zeghib.
Simone Noja (Università di Heidelberg)
The geometry of pure spinor superfield formalism
‘Supersymmetry multiplets’ are a class of representations of the super-Poincaré algebra that underpin all supersymmetric field theories in physics. In this talk, I will explain how the pure spinor superfield formalism offers a systematic method for deriving supersymmetry multiplets from geometric data associated with certain algebraic varieties — namely, nilpotence varieties, which parametrize square-zero elements in a Lie superalgebra. After discussing several examples, I will outline, time permitting, a generalization of the formalism within the framework of derived geometry, in connection with Koszul duality.
Janet C. Vassilev (University of New Mexico)
Resolving monomial ideals in rational normal surfaces
Various techniques have been given to produce free resolutions of monomial ideals in polynomial rings, including the Taylor Resolution and the Barile-Macchia Resolution. We will discuss how to modify these methods to produce resolutions of monomial ideals in rational normal surfaces. This talk is based on joint work with Margherita Barile.
Davide Bolognini (Università Politecnica delle Marche)
The Lehmer complex of a Bruhat interval
In order to investigate the shape of a lower Bruhat interval in a Coxeter group, we introduce the notion of Lehmer complex of a Bruhat interval. It is obtained by using the so-called Lehmer code, which provide a description of a lower Bruhat interval as a multicomplex. In this talk, the basic notions involved are defined and some results regarding the Poincaré polynomials of lower Bruhat intervals in the symmetric group are presented. In particular, it is established a characterization of all possible Poincaré polynomials of smooth Schubert varieties in a flag variety, by setting a correspondence between them and a well-known set of partitions. Moreover, we improve a result due to Bjorner and Frankl and a classical result due to Stanley, both concerning M-sequences.
This is a joint work with Paolo Sentinelli.
Alex Massarenti (Università di Ferrara)
(Uni)rationality problems
We will review the state of the art and some recent results on the rationality and unirationality of conic bundles and hypersurfaces. We will discuss some open problems, and the unirationality of surface conic bundles with eight singular fibers.
Claudemir Fideles Bezerra Jr. (Universidade de Campinas, Brasile)
A generalization of Cayley-Hamilton algebras and an introduction to their geometries
There are several important theorems concerning the subject of matrix embeddings. Many of these results aim to address the following fundamental question: When does a given ring have an embedding into n × n matrices over some commutative ring? An obvious necessary condition is that the ring must satisfy the polynomial identities of n × n matrices, but this condition is not sufficient for n > 2. Procesi proved that an algebra R with trace can be embedded into n × n matrices over some commutative ring if and only if it satisfies the Cayley-Hamilton identity of degree n. Here we recall that the Cayley–Hamilton polynomial of a matrix a can be written as a polynomial whose coefficients are polynomials in the traces of ak, k ≥ 1. Such algebras are known as Cayley-Hamilton algebras. Interestingly, the image of this embedding aligns with a ring of invariants, hinting at potential geometrical applications. The main goal of this talk will be to discuss these results in algebras far beyond Cayley-Hamilton algebras, presenting recent developments and findings in this area. This research is supported by the Sa ̃o Paulo Research Foundation (FAPESP), grant No 2023/04011-9.
Scattered polynomials: their properties, connections and applications
In [6], Sheekey introduced a class of linearized polynomials called scattered, bringing to light their connection to maximum rank-metric codes. Although these polynomials have already appeared in various contexts, such as in [1] and [5], this link with coding theory has significantly advanced their study and investigation, sparking considerable interest in recent years. In this talk, we will explore their relationship with certain subsets of the finite projective line over the finite field of order qn known as maximum scattered linear sets, as well as with codes made up of square matrices of order n equipped with the rank metric. We will present the known examples of scattered polynomials up to date and discuss some of their key properties.
We will also address the classification of maximum scattered linear sets of the finite projective line for small values of n and discuss some characterization results for the examples known
so far. Finally, we will retrace how each scattered polynomial gives rise to a translation plane, as
discussed in [2] and in [4]. This talk is based on the recent survey [3].
[1] A. Blokhuis, M. Lavrauw. Scattered spaces with respect to a spread in PG(n, q). Geom. Dedicata 81(1) (2000), 231-243.
[2] V. Casarino, G. Longobardi, C. Zanella. Scattered linear sets in a finite projective line and translation planes, Linear Algebra Appl. 650 (2022), 286-298.
[3] G. Longobardi. Scattered polynomials: an overview on their properties, connections and applications, submitted to Art Discrete Appl. Math.
[4] G. Longobardi, C. Zanella. A standard form for scattered linearized polynomials and properties of the related translation planes, J. Algebr. Comb. 59(4) (2024), 917-937.
[5] G. Lunardon, O. Polverino. Blocking sets and derivable partial spreads. J. Algebr. Combin. 14 (2001), 49-56.
[6] J. Sheekey. A new family of linear maximum rank distance codes. Adv. Math. Commun. 10(3) (2016), 475-488.
What are Barile-Macchia resolutions?
The aim of the talk is to present some recent developments in the theory of minimal graded free resolutions of ideals defined in a polynomial ring over a field. In this connection, some authors introduced the expression “Barile-Macchia resolution” to denote a notion that is rapidly changing its meaning.
The topics addressed are: commutative algebra, graph theory, homological algebra.
Positivity and rigidity of holomorphic foliations
We begin with the notions of holomorphic foliations and the positivity. The essential point of this talk, consists in understanding the role played by a positivity condition on some object associated to a foliation on the global behaviour of it.
Some remarks on the Bismut Hermitian Einstein condition
An Hermitian metric is said to be *Calabi-Yau with torsion* (CYT in short) if it has vanishing first Bismut–Ricci curvature, namely a natural Ricci-type curvature which coincides with the usual Ricci form when the metric is Kähler. When a Hermitian structure is SKT and CYT, then it is a static point of the puriclosed flow, motivating a huge interest in finding explicit non-trivial examples, where by non trivial we mean not diffeomorphic to a global product of a Kähler-Ricci flat manifold and a Bismut flat space. Moreover, up to now, no non-trivial examples are known. In a joint work with A. Fino and G. Grantcharov, we investigate SKT and CYT structures with parallel Bismut torsion. We first characterize the universal cover of such manifolds in the compact case and we use this characterization to construct the first known non-trivial example of CYT and SKT manifold. Such an example can be described as a mapping torus of a product of a compact Kähler Ricci flat manifold with the 3-sphere or, alternatively, as a total space of a holomorphic fibration with Kähler fibre over the Hopf Surface.
Extendibility of foliations
In the study of any geometric structure, a good understanding of the process of restriction/extension with respect to a subvariety X⊆Y provides a great deal of clarity to the problem. In this talk we will address the extension problem for singular foliations in both the analytic and algebraic settings. Broadly speaking, this involves determining whether, given a foliation F on X and an embedding X⊆Y, there exists a foliation F' on Y that restricts to F on X. We will explore the relation between the positivity of the embedding with respect to the singularities of F and the obstruction for having an extension. In particular, we will show a large class of embeddings and foliations where the extension problem has an affirmative answer, including the cases where Y is the total space of a deformation of Y. This is a joint work with Pablo Perrella.
Genuinely Nonabelian Partial Difference Sets
All combinatorial objects possess a group of symmetries and so research into combinatorial structures often uses tools from group theory. Historically these tools have focused on abelian groups, where the symmetries commute and the analysis of the group is relatively simple. Powerful tools in character theory (for example) have been used to discover objects with commuting symmetries. But the convenient tools of abelian groups are inadequate if the group of symmetries is nonabelian, that is, if some symmetries do not commute. In this talk we explore strongly regular graphs where the approach of abelian groups fails and other techniques are required.
This work includes research with professors James A. Davis, John Polhill and Eric Swartz. A paper related to this talk is here: https://onlinelibrary.wiley.com/doi/10.1002/jcd.21938. I will introduce the ideas in that paper and also briefly discuss a few discoveries made since that paper was published.
An improvement of the Bonnet--Myers theorem via Bakry--Émery Ricci curvature
By using conjugate and disconjugate theorems for second-order linear differential equations, we establish an improvement of the Bonnet--Myers theorem for complete Riemannian manifolds via m-Bakry--Émery Ricci curvature. In contrast to the classical theorem of S.B. Myers (Duke Math. J. 8 (1941), 401--404), our result does not require non-negativity of the $m$-Bakry--Émery Ricci curvature and is new even the $m$-Bakry--Émery Ricci curvature is reduced to the Ricci curvature.
Generic properties of nilpotent algebras
We study which properties of finite-dimensional nilpotent algebras are typical. For example, any r-generated nilpotent algebra of nilpotent class c is isomorphic to a factor-algebra of a free nilpotent algebra F=F(r,c) of rank r>1 and class c>1 by an ideal J. We prove that a typical algebra is obtained iff J belongs to the annihilator (center) of F. We also prove that the typical automorphisms of F are scalar modulo F2. The algebras are not necessarily associative or Lie.
Algebras, defined by identical relations
One of the most important features of identical relations in algebras is that in some important classes, two algebras are isomorphic if and only if they satisfy the same identities. The first decisive result in this area was proven half a century ago by Yuri P. Razmyslov. Recently, his virtually forgotten result reemerged in the literature because it appeared to be stronger than a number of much more recent theorems. The goal of the talk is to describe the current state of research in this intriguing area.
Non-compactness results for homogeneous almost contact and contact Riemannian manifolds
It is a classical result that every homogeneous Riemannian manifold with negative definite Ricci tensor must be noncompact. In particular, every homogeneous Einstein Riemannian manifold (M,g) with Ric=cg, c<0 cannot be compact.
We shall discuss some related results concerning homogeneous η-Einstein almost contact and contact metric manifolds. These are odd-dimensional Riemannian manifolds (M,g) endowed with a mixed real-complex structure; indeed, they carry an almost CR structure (D,J), compatible with the metric, where D ⊂ TM is a smooth distribution of codimension 1 and J: D → D is a partial complex structure on it. The distribution D is the kernel of a fixed globally defined 1-form h and the h-Einstein condition is a meaningful extension of the Einstein condition in this context, namely
Ric = ag + bη ⊗ η, a,b ∈ R.
A systematic introduction to the theory of almost contact metric manifolds is devepoled in the monograph [1]. We shall concentrate on some relevant subclasses of these, like almost cosymplectic and pseudo-Hermitian manifolds.
We shall also present a non-compactness result valid for locally homogeneous, regular contact metric manifolds, under more general assumptions, including the η-Einstein case as a particular one. An example of application of this result will be illustrated, concerning contact metric manifolds which are symmetric CR manifolds according to [4] and their classification developed in [2] and [3].
[1] D.E. Blair: Riemannian geometry of contact and symplectic manifolds, 2nd edn. Progress in Mathematics, vol. 203. Birkhauser, Boston (2010).
[2] D.E. Blair, T. Koufogiorgos, B.J. Papantoniou: Contact metric manifolds satisfying a nullity condition, Israel J. Math., 91 (1995), 189-214.
[3] E. Boeckx: A full classification of contact metric (k, µ)-spaces, Illinois J. Math., 44, (2000), 212-219.
[4] W. Kaup, D. Zaitsev: On symmetric Cauchy-Riemann manifolds, Adv. Math., 149, (2000), 145-181.
[5] A. Lotta, V. Martìn-Molina: Some non-compactness results for locally homogeneous contact metric manifolds, Results Math., 77, (2022), no. 4, Paper No. 150, 18 pp.
[6] A. Lotta, On homogeneous η-Einstein almost cosymplectic manifolds, Beitr. Algebra Geom. (2023). https://doi.org/10.1007/s13366-023-00717-8.
Attractors and their stability
One of the fundamental problems in dynamics is to understand the attractor of a system, i.e. the set where most orbits spent most of the time. As soon as the existence of an attractor is determined, one would like to know if it persists in a family of systems and in which way i.e. its stability. Attractors of one dimensional systems are well understood, and their stability as well. I will discuss attractors of two dimensional systems, starting with the special case of Henon maps. In this setting very little is understood. Already to determine the existence of an attractor is a very difficult problem. I will survey the known results and discuss the new developments in the understanding of attractors, coexistence of attractors and their stability for two dimensional dynamical systems.
[seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories]
Gröbnerian and Gröbner-free techniques on non-associative algebras
In this talk we are investigating to what extent Gröbnerian technologies and the Gröbner-free approach can allow to describe the structure of the non-associative magmas.
We consider a F-vector space V, dimF(V)=n, label and enumerate as S={x1,…,xn} an independent basis of it, and consider on V a non-associative binary operation °: V x V → V and the magma S generated by it. In this setting, Gröbner bases have been studied in several papers which defined as Buchberger reduction the natural reduction and proved that any interreduced set is a reduced Gröbner basis G of the ideal I(G) it generates, so that neither S-pair completions nor criteria are needed. In order to describe such ideal I(G) we make use of the alternative description proposed by Buchberger and Möller in terms of functionals; this requires to define, for each P:=(a1,…,an) ∈ Fn, the functional LP: F{S'} → F, to give an adaptation of Möller Algorithm and state a proper (and trivial) Cerlienco-Mureddu Correspondence, which allows us to prove that
I(G) = {f ∈ F{S'} : LP (f)=0, P Î Fn}.
This allows us to answer the challenging query of Pistone, Riccomagno and Rogantin:
they consider the design ideal
I(F) := {f ∈ k[x1,x2] : f(a,b) = 0, (a,b) ∈ F},
F :={(0,0), (1,-1), (-1,1), (0,1), (1,0)} and the model 1,x1,x12,x2,x22 which is the most symmetric of the models in the statistical fan. But they correctly remark that such model is not a monomial basis related to a Gröbner basis because to distroy symmetry is a feature of Gröbner basis computation. It is sufficient to remove the irrelevant requirement that the monomial basis must be related to some termordering to produce a symmetric model for I(F).
Nearly Kähler metrics and torus symmetry
[seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories ]
Nearly Kähler manifolds are Riemannian spaces equipped with an almost complex structure of special type. In dimension six, nearly Kähler metrics are Einstein with positive scalar curvature, and have interesting connections with $G_2$ and spin geometry. At present there are very few compact examples, which are either homogeneous or of cohomogeneity one. In this talk I will explain a theory of nearly Kähler six-manifolds with two-torus symmetry. The torus-action yields a multi-moment map, which we use as a Morse function to understand the structure of the whole manifold. In particular, we show how the local geometry of a nearly Kähler six-manifold can be recovered from three-dimensional data, and discuss connections with GKM theory.
Some rigidity results for stable minimal hypersurfaces
[seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories ]
In this talk I will describe two recent results concerning the rigidity of complete, immersed, orientable, stable minimal hypersurfaces: they are hyperplane in R4 while they do not exist in some positively curved closed Riemannian (n+1)-manifold when n < 6. The first result was proved also by Chodosh and Li, and the second is a consequence of a more general result concerning minimal surfaces with finite index. Both theorems rely on a conformal method, inspired by a classical paper of Fischer-Colbrie. I will also present an application of these techniques to the study of critical metrics of a quadratic curvature functional.
Einstein metrics and Ricci solitons
[seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories ]
In this talk I will show some rigidity results for Einstein metrics with positive scalar curvature and shrinking Ricci solitons.
Non-linear MRD codes from cones over exterior sets
Let PG(m,qn) be an m-dimensional projective space over the finite field with qn elements. Let A and B be two distinct points of PG(m,qn) and let Φ be a collineation, with accompanying field automorphism σ, between the stars (pencils if m=2) of lines through A and B such that the line AB is not mapped into itself and the subspace spanned by the lines AB, Φ(AB), Φ-1(AB) has dimension min{3,m}. The set X consisting of points of intersection of corresponding lines under Φ is called σ-normal rational curve.
A set of n x n matrices with entries in GF(q) of size qn(n-d+1) is called maximum rank distance code or MRD code with parameters (n,n,q;d) if the rank of the difference of any two of its elements is at least d.
In this talk, it will be outlined how starting from X, it is possible to obtain a new family of non-linear (n,n,q;d)-MRD codes for any n > 2, 1 < d < n, and d = m.
Magnetic Jacobi fields in almost contact metric manifolds
[seminario cofinanziato dal PRIN2022 Interactions between Geometric Structures and Function Theories ]
The first variation of the Landau Hall functional on a Riemannian manifold leads to the notion of magnetic curves. Computing the second variation, we obtain the equation of a Jacobi-type field along a magnetic curve. In this talk we focus on the contact magnetic trajectories in Sasakian and cosymplectic manifolds (as ambient space) emphasising the main differences between the two cases. We will give several examples.
This talk is based on some joint papers:
M.I. Munteanu, \emph{Magnetic geodesics in (almost) cosymplectic Lie groups of dimension 3}, Mathematics, (Special Issue: Topics in Differential Geometry), 10 (2022) 4, art. 544.
J. Inoguchi, M.I. Munteanu, \emph{Magnetic Jacobi fields in 3-dimensional Sasakian space forms}, J. Geom. Analysis, 32 (2022) 3, art. 96.
M.I. Munteanu, A.I. Nistor, \emph{Magnetic Jacobi fields in cosymplectic 3-dimensional manifolds}, Mathematics, (Special Issue: Differential Geometry: structures on manifolds and their applications), 9 (2021) 24 art. 3220.
J. Inoguchi, M.I. Munteanu, \emph{Magnetic Jacobi fields in Sasakian space forms}, Mediterranean J. Mathematics, 20 (2023) art. 29.
Images of polynomials on algebras
The Lvov-Kaplansky conjecture states that the image of a multilinear polynomial evaluated on the matrix algebra over a field is a vector space. This result has only been proven for matrices of order 2, with some restriction on the base field. In this talk, we will present the topic of images of polynomials in algebras, and recent results on some variations of the Lvov-Kaplansky conjecture, considering different (not necessarily associative) algebras as well as algebras with additional structures.
Global Properties of Quaternionic Regular Functions
I will survey some basic facts about "regular functions" in the quaternionic setting.
First, I will compare the non-equivalent notion of regularity and the I will specialise in the theory of slice regularity (possibly in relation to monogenicity). Then I will discuss covering properties and algebraic structure for slice regular functions.
Bence Csajbok (Politecnico di Bari)
Small, complete subsets of groups without a 3-term arithmetic progression
Let G denote an Abelian group of odd order, written additively. A 3-term arithmetic progression of G, 3-AP for short, is a set of three distinct elements of G of the form g, g+d, g+2d, for some elements g, d of G.
Let S denote a subset of G. Then S is called 3-AP-free if it does not contain a 3-AP. Moreover, S is called complete 3-AP-free if S is 3-AP-free and it is not contained in a larger 3-AP-free set. We will say that S is 3-AP saturating if for each element x of G \ S there is a 3-AP of G consisting of x and two elements of S. Clearly, S is complete 3-AP-free if and only if it is 3-AP-free and 3-AP saturating.
A classical problem in additive combinatorics is to obtain good upper and lower bounds for the maximal size of a 3-AP-free set. In the special case when G=GF(3)n (GF(q) denotes the finite field of order q) then the 3-AP-free sets are exactly the affine point sets without a collinear triple. In general, point sets of V=GF(q)n without a collinear triple are called (affine) caps. In finite geometry it is a classical problem to find small complete caps (a cap is complete if it is not contained in a larger cap) and small saturating sets (a point set S is saturating if for each point x of V \ S there is a collinear triple ofV consisting of x and two elements of S).
In this talk I will present constructions of complete 3-AP-free sets and 3-AP saturating sets whose size is close to the trivial lower bound. We will be mostly concerning the cases when G is a finite vector space or a cyclic group.
This is a joint work and work in progress with Zoltán Lóránt Nagy.
Leonardo Câmara (Federal University of Espírito Santo, Brasile)
Residues for maps generically transverse to distributions
We prove the existence of residues related to tangency points of maps generically transverse to locally free holomorphic distribution. We provide some formulas relating these residues to the characteristic classes of these distributions. This is a joint work with Mauricio Corrêa.
Aron Simis (Universidade de Pernambuco, Brasile)
The Bourbaki degree of a plane projective curve
Bourbaki sequences and Bourbaki ideals have been studied by several authors since its inception sixty years ago circa. Generic Bourbaki sequences have been thoroughly examined by the senior author with Ulrich and Vasconcelos, but due to their nature, no numerical invariant was immediately available.
The present work introduces the Bourbaki degree as the algebraic multiplicity of a Bourbaki ideal corresponding to choices of minimal generators of minimal degree of the given graded module. Since the main intent is a study of plane curve singularities via this new numerical invariant, accordingly, quite naturally, the focus is on the case where the standing graded module is the first syzygy module of the gradient ideal of a reduced form f ∈ k[x, y, z] – i.e., the main component of the module of logarithmic derivations of the corresponding curve. The overall goal of this project is to allow for a tiny facet of classification of projective plane curves based on the behavior of this new numerical invariant, with emphasis on results about its lower and upper bounds. In particular, we revisit results of du Plessis and Wall, and of Dimca and co-authors.
(Joint work with Marcos Jardim and Abbas N. Nejad)
Sabino Di Trani (Sapienza Università di Roma)
Linear Degenerations of Flag Variety: a Tale of Geometry and Combinatoric
Linear Degenerations of the Flag Variety arise as very natural generalizations of the Complete Flag Variety and their geometrical properties very often appear to be linked with interesting combinatorial patterns.
In the first part of the talk I am going to introduce these objects, discuss their remarkable properties and state the main problems in this interesting research area.
In the second part of the talk I will focus on a special class of linear degenerations, the Flat Degenerations, that have the remarkable property of being equidimensional algebraic varieties of the same dimension as the Complete Flag Variety.
Finally, if there is enough time, I will show how suitable torus actions and quiver representation theory can be used in this setting to prove some new results about the smooth locus in Flat Linear Degenerations.
Viola Siconolfi (PoliBa)
Zeta functions for class two nilpotent groups
The notion of Zeta function for groups was introduced in a seminal paper from Grunewald, Segal and Smith and proved to be a powerful tool to study the subgroup growth in some classes of groups. In this seminar I will introduce this Zeta function presenting some general properties for this object. I will then focus on some results obtained for class two nilpotent groups. In particular, I will describe some combinatorial tecniques used to tackle this problem, namely the study of series associated to polyhedral integer cones.
This is a joint work with Christopher Voll and Marlies Vantomme.
Roberto Pignatelli (Università di Trento)
Varieties of small volume
This is a joint work with S. Coughlan, Y. Hu e T. Zhang. In the theory of the algebraic varieties of general type the key invariants are the (geometric) genus and the volume. I will discuss the known relations among these two numbers, and then discuss the case when the volume is minimal respect to the genus. In particular I will present the classical results of M. Noether-F-Enriques-E. Horikawa in dimension 2 and then present the analogous result we achieved in dimension 3.
Nicola Picoco (UniBa)
Cayley–Bacharach property: a little history and some applications
The Cayley–Bacharach condition is a very classical property that found its roots in ancient and classical geometry. In this talk we retrace the main steps through the history that have led to the modern formulation. We show how be- ing Cayley–Bacharach with respect to the complete linear system of hypersurfaces of given degree forces a set of points in the projective space to lie on a reduced curve of low degree. In particular, starting from a result for points in the projec- tive plane due to Lopez and Pirola, we present some partial extensions to any Pn. Moreover, in a joint work with F. Bastianelli, we study the Cayley–Bacharach con- dition for points on Grassmannians; we rephrase the Cayley–Bacharach condition as a property for linear subspaces and we prove that this property affects their geometry. Namely, we get an upper bound for the dimension of the linear span of linear subspaces satisfying Cayley–Bacharach conditions. Finally we apply these results to different topics. The main one is the computation of the covering go- nality of the 3-fold and 4-fold symmetric product of a smooth complex projective curve of genus at least 4 and 5 respectively. Other applications concern linear se- ries on curves lying on smooth surfaces in P3 and the so-called correspondences with null trace.
Indira Chatterji (Université Côte d'Azur)
Hyperbolic groups
A group il called finitely generated if every element can be expressed in terms of a finite subset of elements of the group. We will be discussing hyperbolic groups, a class of finitely generated groups including fundamental groups of closed negatively curved manifolds, as well as some generalizations.
Elena Martinengo (Università di Torino)
Algebre di Lie differenziali graduate, teoria delle deformazioni e luoghi di Brill-Noether
Nella prima parte di questo seminario introdurremo le algebre di Lie differenziali graduate (dgLa) e spiegheremo il loro uso in teoria delle deformazioni, illustrando molti esempi classici in cui esse vengono usate in maniera vantaggiosa. Nella seconda parte ci concentreremo sullo studio dei luoghi di Brill-Noether. Sia C una curva liscia proiettiva, i luoghi di Brill-Noether W_d^k sono spazi dei sistemi lineari su C di grado d e di dimensione proiettiva almeno k. Sono classicamente note proprietà di tali luoghi, quali la connessione, la dimensione, i luoghi singolari e ci sono vari lavori abbastanza recenti in cui tali risultati vengono generalizzati al caso di fibrati vettoriali di qualunque rango e a varietà lisce proiettive di qualunque dimensione. In un lavoro con Donatella Iacono, ci occupiamo di studiare i luoghi di fibrati vettoriali aventi almeno un numero fissato di sezioni indipendenti su una varietà proiettiva liscia. Usando le algebre di Lie differenziali graduate siamo in grado di riottenere e generalizzare alcuni risultati che riguardano lo spazio e il cono tangente e i luoghi singolari di tali spazi.
Janet Vassilev (University of New Mexico)
Differential operators on toric face rings and differentially fixed ideals
Dimiter Vassilev (University of New Mexico)
The fractional Yamabe equation on homogeneous groups
seminari proposti e organizzati da Margherita Barile e Annunziata Loiudice
https://www.dm.uniba.it/it/ricerca/conferenze/2023/vassilev-barile
https://www.dm.uniba.it/it/ricerca/conferenze/2023/vassilev-loiudice
Janet Vassilev: Toric face rings are a generalization of both Stanley-Reisner rings and affine semigroup rings. Our goal in this talk is two-fold: (1) We will describe the ring of differential operators of a toric face ring $R$ using the rings of differential operators on affine semigroup rings which are algebra retracts of $R$, and (2) we will give a complete characterization of monomial ideals in an affine semigroup ring which are fixed by a differential operator. This is joint work coming from two projects with Berkesch, Chan, Klein, Matusevich and Page and with Miller and Taylor.
Dimiter Vassilev: The general themes of the talk are Dirichlet forms, fractional operators and associated Sobolev type spaces on groups of homogeneous type. Our results lead to explicit integral formulas of the infinitesimal generators, which are the studied fractional operators, and embedding theorems between the relevant spaces. The considered groups are not assumed to be Carnot groups or to satisfy a H\"ormander type conditions. Finally, we will describe a result on sharp asymptotic decay of solutions to non-linear equations modeled on the fractional Yamabe equation.
Homare Tadano (Yamaguchi University)
A Zoo of Myers-type Theorems
One of the important issues in differential geometry is to study the relation between curvature and topology of Riemannian manifolds. In this talk, I would like to introduce various generalizations and improvements of the classical Myers theorem via some modifications of the Ricci curvature.If time permits, I would also like to discuss some relations between topology and geometric structures on Riemannian manifolds such as Myers-type theorems on Sasaki manifolds.
Daniele Bartoli (Università degli Studi di Perugia)
Relevant classes of polynomial functions with applications to Coding Theory and Cryptography
A number of different polynomial functions over finite fields have relevant applications in applied areas of Mathematics, as Cryptography or Coding Theory. Among them, APN functions, PN functions, APN permutations, permutation polynomials have been widely studied in the recent years.
In order to investigate non-existence of such functions or to provide constructions of infinite families, algebraic varieties over finite fields are a useful tool. In this direction, a key ingredient is an estimate of the number of rational points of such algebraic varieties and therefore Hasse-Weil type theorems (Lang-Weil, Serre,. . . ) play a fundamental role.
The aim of this talk is to summarize recent results in this direction.
Daniele Angella (Università di Firenze)
The Chern-Ricci flow on Inoue-Bombieri surfaces
In the tentative to move from the Kähler to the non-Kähler setting, one can formulate several problems concerning Hermitian metrics on complex manifolds with special curvature properties. Among these problems, we mention the existence of Hermitian metrics with constant scalar curvature with respect to the Chern connection, and the generalizations of the Kähler-Einstein condition to the non-Kähler setting. They are usually translated and attacked as analytic pdes.
In this context, the Chern-Ricci flow plays an useful role. The Chern-Ricci flow is a parabolic evolution equation for Hermitian metrics that extends the Kähler-Ricci flow to Hermitian manifolds. It is expected that the behaviour of solutions of the Chern-Ricci flow deeply reflects the underlying complex structure. In particular, understanding the behaviour of the Chern-Ricci flow on non-Kähler compact complex surfaces is particularly interesting, due to the fact that minimal class VII surfaces are not yet completely classified.
In this talk, we study the problem of uniform convergence of the normalized Chern-Ricci flow on Inoue-Bombieri surfaces with Gauduchon metrics.
The talk is based on a joint work with Valentino Tosatti, and on collaborations and discussions with Simone Calamai, Francesco Pediconi, Cristiano Spotti, and others.
Francesco Bastianelli (UniBa)
Measures of irrationality for projective varieties
A projective variety X of dimension n is said to be rational if it is birationally isomorphic to the n-dimensional projective space P^n, i.e. if it contains an open dense subset isomorphic to an open dense subset of P^n.
Due to our knowledge about projective spaces, it is important to understand whether a given variety is rational or satisfies some property of rational varieties.
In addition, there has been a great deal of recent interest and progress in studying the so-called “measures of irrationality”, i.e. birational invariants that somehow measure how a given variety is far from satisfying properties of rational varieties.
In this talk, I will discuss these invariants and I will focus on various recent results concerning measures of irrationality for hypersurfaces in P^n.
Michela Ceria (PoliBa)
On the geometry of (q + 1)-arcs of PG(3, q), q even
Lucio Centrone (UniBa)
Specht property and Gelfand's conjecture
Mauricio Barros Correa (UniBa)
Algebro-geometric methods in holomorphic distributions and foliations
The theory of distributions and foliations has its origins in the studies of nineteenth-century mathematicians such as Grassmann, Jacobi, Clebsch, Cartan and Frobenius. They were motivated by the fundamental work due to Pfaff, who proposed a geometric approach to the study of differential equations. Distributions and foliations play an important role in several subjects from differential, complex, algebraic and Poisson geometries. The qualitative study of foliations induced by complex polynomial differential equations was investigated by Poincaré, Darboux and Painlevé. In this talk I will discuss some Algebro-geometric methods in the study of holomorphic distributions and foliations, their moduli spaces and topological invariants.