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Gianni Manno

Publications and source records attributed to Gianni Manno.

35 records · Page 2Linked to original sources
arXiv2018

The geometry of marked contact Engel structures

A contact twisted cubic structure (M,C,S) is a 5-dimensional manifold M together with a contact distribution C and a bundle S of twisted cubics that is compatible with the conformal symplectic form on C. In Engel's classical work, the Lie algebra of the exceptional Lie group G_2 was realized as the symmetry algebra of the most symmetric contact twisted cubic structure; we thus refer to this one as the contact Engel structure. In the present paper we equip the contact Engel structure with a smooth section s: M-> S that `marks' a point in each twisted cubic. We study the local geometry of the resulting structures (M,C,S,s), which we call marked contact Engel structures. Equivalently, our study can be viewed as a study of foliations of M by curves whose tangent directions are everywhere contained in S. We provide a complete set of local invariants of marked contact Engel structures, we classify all homogeneous models with symmetry groups of dimension greater than 5, and we prove an analogue of the classical Kerr theorem from relativity.

math.DG↗
arXiv2018

On Lie algebras responsible for zero-curvature representations and Backlund transformations of (1+1)-dimensional scalar evolution PDEs

Zero-curvature representations (ZCRs) are one of the main tools in the theory of integrable PDEs. In particular, Lax pairs for $(1+1)$-dimensional PDEs can be interpreted as ZCRs. In [arXiv:1303.3575], for any $(1+1)$-dimensional scalar evolution equation $E$, we defined a family of Lie algebras $F(E)$ which are responsible for all ZCRs of $E$ in the following sense. Representations of the algebras $F(E)$ classify all ZCRs of the equation $E$ up to local gauge transformations. Also, using these algebras, one obtains necessary conditions for existence of a Backlund transformation between two given equations. The algebras $F(E)$ are defined in [arXiv:1303.3575] in terms of generators and relations. In this approach, ZCRs may depend on partial derivatives of arbitrary order, which may be higher than the order of the equation $E$. The algebras $F(E)$ generalize Wahlquist-Estabrook prolongation algebras, which are responsible for a much smaller class of ZCRs. In this preprint we prove a number of results on $F(E)$ which were announced in [arXiv:1303.3575]. We present applications of $F(E)$ to the theory of Backlund transformations in more detail and describe the explicit structure (up to non-essential nilpotent ideals) of the algebras $F(E)$ for a number of equations of orders $3$ and $5$.

nlin.SI↗
arXiv2017

Lowest degree invariant 2nd order PDEs over rational homogeneous contact manifolds

For each simple Lie algebra $\mathfrak{g}$ (excluding, for trivial reasons, type ${\sf C}$) we find the lowest possible degree of an invariant second-order PDE over the adjoint variety in $\mathbb{P}\mathfrak{g}$, a homogeneous contact manifold. Here a PDE $F(x^i,u,u_i,u_{ij})=0$ has degree $\le d$ if $F$ is a polynomial of degree $\le d$ in the minors of $(u_{ij})$, with coefficients functions of the contact coordinates $x^i$, $u$, $u_i$ (e.g., Monge-Ampère equations have degree 1). For $\mathfrak{g}$ of type ${\sf A}$ or ${\sf G}$ we show that this gives all invariant second-order PDEs. For $\mathfrak{g}$ of type ${\sf B}$ and ${\sf D}$ we provide an explicit formula for the lowest-degree invariant second-order PDEs. For $\mathfrak{g}$ of type ${\sf E}$ and ${\sf F}$ we prove uniqueness of the lowest-degree invariant second-order PDE; we also conjecture that uniqueness holds in type ${\sf D}$.

math.DG↗
arXiv2017

Contact manifolds, Lagrangian Grassmannians and PDEs

In this paper we review a geometric approach to PDEs. We mainly focus on scalar PDEs in n independent variables and one dependent variable of order one and two, by insisting on the underlying (2n+1)-dimensional contact manifold and the so-called Lagrangian Grassmannian bundle over the latter. This work is based on a 30-hours Ph.D course given by two of the authors (GM and GM). As such, it was mainly designed as a quick introduction to the subject for graduate students. But also the more demanding reader will be gratified, thanks to the frequent references to current research topics and glimpses of higher-level mathematics, found mostly in the last sections.

math.DG↗
arXiv2017

On Lie algebras responsible for zero-curvature representations of multicomponent (1+1)-dimensional evolution PDEs

Zero-curvature representations (ZCRs) are one of the main tools in the theory of integrable $(1+1)$-dimensional PDEs. According to the preprint arXiv:1212.2199, for any given $(1+1)$-dimensional evolution PDE one can define a sequence of Lie algebras $F^p$, $p=0,1,2,3,\dots$, such that representations of these algebras classify all ZCRs of the PDE up to local gauge equivalence. ZCRs depending on derivatives of arbitrary finite order are allowed. Furthermore, these algebras provide necessary conditions for existence of Backlund transformations between two given PDEs. The algebras $F^p$ are defined in arXiv:1212.2199 in terms of generators and relations. In the present paper, we describe some methods to study the structure of the algebras $F^p$ for multicomponent $(1+1)$-dimensional evolution PDEs. Using these methods, we compute the explicit structure (up to non-essential nilpotent ideals) of the Lie algebras $F^p$ for the Landau-Lifshitz, nonlinear Schrodinger equations, and for the $n$-component Landau-Lifshitz system of Golubchik and Sokolov for any $n>3$. In particular, this means that for the $n$-component Landau-Lifshitz system we classify all ZCRs (depending on derivatives of arbitrary finite order), up to local gauge equivalence and up to killing nilpotent ideals in the corresponding Lie algebras. The presented methods to classify ZCRs can be applied also to other $(1+1)$-dimensional evolution PDEs. Furthermore, the obtained results can be used for proving non-existence of Backlund transformations between some PDEs, which will be described in forthcoming publications.

nlin.SI↗
arXiv2016

Hydrodynamic-type systems describing 2-dimensional polynomially integrable geodesic flows

Starting from a homogeneous polynomial in momenta of arbitrary order we extract multi-component hydrodynamic-type systems which describe 2-dimensional geodesic flows admitting the initial polynomial as integral. All these hydrodynamic-type systems are semi-Hamiltonian, thus implying that they are integrable according to the generalized hodograph method. Moreover, they are integrable in a constructive sense as polynomial first integrals allow to construct generating equations of conservation laws. According to the multiplicity of the roots of the polynomial integral, we separate integrable particular cases.

math.DG↗
arXiv2016

Meta-Symplectic Geometry of $3^{\rm rd}$ Order Monge-Ampère Equations and their Characteristics

This paper is a natural companion of [Alekseevsky D.V., Alonso Blanco R., Manno G., Pugliese F., Ann. Inst. Fourier (Grenoble) 62 (2012), 497-524, arXiv:1003.5177], generalising its perspectives and results to the context of third-order (2D) Monge-Ampère equations, by using the so-called "meta-symplectic structure" associated with the 8D prolongation $M^{(1)}$ of a 5D contact manifold $M$. We write down a geometric definition of a third-order Monge-Ampère equation in terms of a (class of) differential two-form on $M^{(1)}$. In particular, the equations corresponding to decomposable forms admit a simple description in terms of certain three-dimensional distributions, which are made from the characteristics of the original equations. We conclude the paper with a study of the intermediate integrals of these special Monge-Ampère equations, herewith called of Goursat type.

math.DG↗
arXiv2016

Completely exceptional $2^\textrm{nd}$ order PDEs via conformal geometry and BGG resolution

By studying the development of shock waves out of discontinuity waves, in 1954 P. Lax discovered a class of PDEs, which he called 'completely exceptional', where such a transition does not occur after a finite time. A straightforward integration of the completely exceptionality conditions allowed Boillat to show that such PDEs are actually of Monge-Ampere type. In this paper, we first recast these conditions in terms of characteristics, and then we show that the completely exceptional PDEs, with 2 or 3 independent variables, can be described in terms of the conformal geometry of the Lagrangian Grassmannian, where they are naturally embedded. Moreover, for an arbitrary number of independent variables, we show that the space of r-th degree sections of the Lagrangian Grassmannian can be resolved via a BGG operator. In the particular case of 1st degree sections, i.e., hyperplane sections or, equivalently, Monge-Ampere equations, such operator is a close analog of the trace-free second fundamental form.

math.DG↗
arXiv2014

Ordinary differential equations described by their Lie symmetry algebra

The theory of Lie remarkable equations, i.e. differential equations characterized by their Lie point symmetries, is reviewed and applied to ordinary differential equations. In particular, we consider some relevant Lie algebras of vector fields on $\mathbb{R}^k$ and characterize Lie remarkable equations admitted by the considered Lie algebras.

math-ph↗
arXiv2014

On the extendability of parallel sections of linear connections

Let $π:E\to M$ be a vector bundle over a simply connected manifold and $\nabla$ a linear connection in $π$. Let $σ: U \rightarrow E$ be a $\nabla$-parallel section of $π$ defined on a connected open subset $U$ of $M$. We give sufficient conditions on $U$ in order to extend $σ$ to the whole $M$. We mainly concentrate to the case when $M$ is a $2$-dimensional simply connected manifold.

math.DG↗
arXiv2010

Contact geometry of multidimensional Monge-Ampère equations: characteristics, intermediate integrals and solutions

We study the geometry of multidimensional scalar $2^{nd}$ order PDEs (i.e. PDEs with $n$ independent variables) with one unknown function, viewed as hypersurfaces $\mathcal{E}$ in the Lagrangian Grassmann bundle $M^{(1)}$ over a $(2n+1)$-dimensional contact manifold $(M,\mathcal{C})$. We develop the theory of characteristics of the equation $\mathcal{E}$ in terms of contact geometry and of the geometry of Lagrangian Grassmannian and study their relationship with intermediate integrals of $\mathcal{E}$. After specifying the results to general Monge-Ampère equations (MAEs), we focus our attention to MAEs of type introduced by Goursat, i.e. MAEs of the form $$ \det|\frac{\partial^2 f}{\partial x^i\partial x^j}-b_{ij}(x,f,\nabla f)\|=0. $$ We show that any MAE of the aforementioned class is associated with an $n$-dimensional subdistribution $\mathcal{D}$ of the contact distribution $\mathcal{C}$, and viceversa. We characterize this Goursat-type equations together with its intermediate integrals in terms of their characteristics and give a criterion of local contact equivalence. Finally, we develop a method of solutions of a Cauchy problem, provided the existence of a suitable number of intermediate integrals.

math.DG↗
arXiv2007

Normal forms for parabolic Monge-Ampere equations

We find normal forms for parabolic Monge-Ampere equations. Of these, the most general one holds for any equation admitting a complete integral. Moreover, we explicitly give the determining equation for such integrals; restricted to the analytic case, this equation is shown to have solutions. The other normal forms exhaust the different classes of parabolic Monge-Ampere equations with symmetry properties, namely, the existence of classical or nonholonomic intermediate integrals. Our approach is based on the equivalence between parabolic Monge-Ampere equations and particular distributions on a contact manifold, and involves a classification of vector fields lying in the contact structure. These are divided into three types and described in terms of the simplest ones (characteristic fields of first order PDE's).

math.DG↗
arXiv2006

On the geometry of Grassmannian equivalent connections

We introduce the equation of n-dimensional totally geodesic submanifolds of a manifold E as a submanifold of the second order jet space of n-dimensional submanifolds of E. Next we study the geometry of n-Grassmannian equivalent connections, that is linear connections without torsion admitting the same equation of n-dimensional totally geodesic submanifolds. We define the n-Grassmannian structure as the equivalence class of such connections, recovering for n=1 the case of theory of projectively equivalent connections. By introducing the equation of parametrized n-dimensional totally geodesic submanifolds as a submanifold of the second order jet space of the trivial bundle on the space of parameters, we discover a relation of covering between the `parametrized' equation and the `unparametrized' one. After having studied symmetries of these equations, we discuss the case in which the space of parameters is equal to R^n.

math.DG↗
arXiv2006

Higher symmetries of the elliptic Euler-Darboux equation

We find a remarkable subalgebra of higher symmetries of the elliptic Euler-Darboux equation. To this aim we map such equation into its hyperbolic analogue already studied by Shemarulin. Taking into consideration how symmetries and recursion operators transform by this complex contact transformation, we explicitly give the structure of this Lie algebra and prove that it is finitely generated. Furthermore, higher symmetries depending on jets up to second order are explicitly computed.

math-ph↗
arXiv2003

The geometry of finite order jets of submanifolds and the variational formalism

We study the geometry of jets of submanifolds with special interest in the relationship with the calculus of variations. We give a new proof of the fact that higher order jets of submanifolds are affine bundles; as a by-product we obtain a new expression for the associated vector bundles. We use Green-Vinogradov formula to provide coordinate expressions for all variational forms, i.e., objects in the finite-order variational sequence on jets of submanifolds. Finally, we formulate the variational problem in the framework of jets of submanifolds by an intrinsic geometric language, and connect it with the variational sequence. Detailed comparison with literature is provided throughout the paper.

math.DG↗