arXiv subjects

Paolo Lorenzoni

Publications and source records attributed to Paolo Lorenzoni.

At least 19 recordsLinked to original sources

arXiv2026

Haantjes torsion and integrability: a proof of Bolsinov-Konyaev-Matveev's conjecture

We prove a conjecture formulated by Bolsinov, Konyaev and Matveev in [7] stating that, integrability of a system of hydrodynamic type ${\bf u}_t=A({\bf u}) {\bf u}_x$ with $\mathfrak{gl}$-regular $A$ at a point $p$ implies the vanishing of the Haantjes tensor of $A$ and of all its symmetries in a neighborhood of $p$. As a consequence, leveraging on the result of [8], in a neighbourhood of an algebraically generic point, any integrable system of hydrodynamic type defined by a $\mathfrak{gl}$-regular operator field can be written as ${\bf u}_t=X({\bf u})\circ {\bf u}_x$ where $X$ is a vector field and $\circ$ is a commutative associative product satisfying Hertling-Manin conditions.

math-ph↗

arXiv2026

Cyclic F-manifolds, distinguished connections and integrability

We show that the geometry of Hertling-Manin F-manifolds $(M,\circ,e)$ provide the appropriate theoretical framework for studying the integrability of quasilinear systems of first-order evolutionary partial differential equations of the form ${\bf u}_t=X\circ {\bf u}_x$ (F-systems) under the mild assumption that the unit vector field is cyclic with respect to the operator of multiplication by the vector field $X$. This approach is very general and allows us to treat even non-regular systems that were previously beyond the scope of existing techniques. Like in the regular case the information about integrability is contained in a torsionless connection associated with the system and the integrability condition reduces to a geometric condition involving the Riemann tensor of the connection and the structure functions of the product. We prove that a locally conservative F-system is integrable and, in the analytic setting, also the converse statement, thereby providing a full characterization of integrability. Moreover, in the analytic case, we prove the existence of a family of analytic symmetries providing, in principle, the unique local analytic solution of the Cauchy problem through the generalised hodograph method.

math-ph↗

arXiv2026

Gibbons-Tsarev type systems and Eventual identities

We show that non-diagonalisable reductions of the dKP equation associated with regular non-semisimple $F$-manifolds cannot exist. The proof is based on the derivation and study of a generalised Gibbons--Tsarev system (gGT system) in the non-semisimple/non-diagonalisable setting. Remarkably, a class of solutions of the gGT system is defined by eventual identities of the underlying regular $F$-manifold structure. Furthermore, we use these vector fields to construct integrable reductions of Pavlov's hydrodynamic chain. In this case, the corresponding solutions are defined for any choice of Jordan block structure of the operator of multiplication by an eventual identity.

math-ph↗

arXiv2026

Generalised (bi-)Hamiltonian structures of hydrodynamic type and (bi-)flat F-manifolds

We introduce the notions of generalised (bi-)Hamiltonian structures which generalise naturally the (bi-)Hamiltonian structures of evolutionary partial differential equations. In the hydrodynamic case, these structures are characterised in terms of geometric data. Furthermore, we show that a generalised (bi)-Hamiltonian structure of hydrodynamic type can be associated with any (bi-)flat F-manifold, and it is compatible with the corresponding principal hierarchy.

math-ph↗

arXiv2026

Compatible pairs of Hamiltonian operators of the first and third orders

We compute general compatibility conditions between a weakly nonlocal homogeneous Hamiltonian operator and a third-order homogeneous Hamiltonian operator. Such operators determine a bi-Hamiltonian structure for many integrable PDEs (Korteweg--De Vries, Camassa--Holm, dispersive water waves, Dym, WDVV and others). Remarkably, the full set of conditions is purely algebraic and the first-order operator is completely determined by commuting systems of conservation laws that are Hamiltonian with respect to a third-order operator. We illustrate the above results with several examples, some of which, concerning WDVV equations, are new.

nlin.SI↗

arXiv2025

Hamiltonian formalism for non-diagonalisable systems of hydrodynamic type

We study the system of first order PDEs for pseudo-Riemannian metrics governing the Hamiltonian formalism for systems of hydrodynamic type. In the diagonal setting the integrability conditions ensure the compatibility of this system and, thanks to a classical theorem of Darboux, the existence of a family of solutions depending on functional parameters. In this paper we study the generalisation of this result to a class of non-diagonalisable systems of hydrodynamic type that naturally generalises Tsarev's integrable diagonal systems.

math-ph↗

arXiv2025

The generalised hodograph method for non-diagonalisable integrable systems of hydrodynamic type

We extend the generalised hodograph method to regular non- diagonalisable integrable systems of hydrodynamic type, in light of the relation between such systems and F-manifolds with compatible connection. The method allows the construction of solutions starting from the symmetries of the system. In the diagonal case, the completeness of the symmetries follows from the integrability conditions that ensure the applicability of a Darbouxâ€™s theorem on Pfaffian systems. In the regular non-diagonalisable case the validity of this theorem relies on some further assumptions that we discuss in detail. Under these assumptions, the method provides the general solution as in Tsarevâ€™s diagonal case.

nlin.SI↗

arXiv2024

Integrable hierarchies and F-manifolds with compatible connection

Building on the interplay between geometry and integrability, we show that F-manifolds with compatible connection $(\nabla,\circ,e)$ are the geometric counterpart of integrable systems of quasilinear first order evolutionary PDEs. We consider F-manifolds equipped with an Euler vector field and assume that the operator $L=E\circ$ is regular. This generalises previous results in the semisimple context. As an example we study regular F-manifolds with compatible connection $(\nabla,\circ,e,E)$ associated with integrable hierarchies obtained from the solutions of the equation $d\cdot d_L \,a_0=0$ by applying the construction of [27]. We show that $n$-dimensional F-manifolds associated to operators $L$ with $r\le n$ Jordan blocks $L_α$ of size $m_α$ are classified by $n$ arbitrary functions of a single variable, where each block $L_α$ contributes with $m_α$ functions of the variable appearing in the diagonal of the block. In the case of a single Jordan block of arbitrary size we show that flat connections $\nabla$ correspond to linear solutions $a_0$. This generalises part of the construction of [31] where special linear solutions were considered. We illustrate the construction in dimensions $2,3,$ and $4$ for any choice of Jordan canonical form and any choice of the corresponding solution $a_0$. In these dimensions we have that linear solutions define bi-flat F-manifolds, and that the special linear solutions studied in [31] are related to Riemannian F-manifolds with Killing unit vector field. We conjecture that this is true in general.

math-ph↗

arXiv2024

Bi-flat F-structures as differential bicomplexes and Gauss-Manin connections

We show that a bi-flat F-structure $(\nabla,\circ,e,\nabla^*,*,E)$ on a manifold $M$ defines a differential bicomplex $(d_{\nabla},d_{E\circ\nabla^*})$ on forms with value on the tangent sheaf of the manifold. Moreover, the sequence of vector fields defined recursively by $d_{\nabla}X_{(α+1)}=d_{L\nabla^*}X_{(α)}$ coincide with the coefficients of the formal expansion of the flat local sections of a family of flat connections $\nabla^{GM}$ associated with the bi-flat structure. In the case of Dubrovin-Frobenius manifold the connection $\nabla^{GM}$ (for suitable choice of an auxiliary parameter) can be identified with the Levi-Civita connection of the flat pencil of metrics defined by the invariant metric and the intesection form.

math.DG↗

arXiv2022

Semisimple flat F-manifolds in higher genus

In this paper, we generalize the Givental theory for Frobenius manifolds and cohomological field theories to flat F-manifolds and F-cohomological field theories. In particular, we define a notion of Givental cone for flat F-manifolds, and we provide a generalization of the Givental group as a matrix loop group acting on them. We show that this action is transitive on semisimple flat F-manifolds. We then extend this action to F-cohomological field theories in all genera. We show that, given a semisimple flat F-manifold and a Givental group element connecting it to the constant flat F-manifold at its origin, one can construct a family of F-CohFTs in all genera, parameterized by a vector in the associative algebra at the origin, whose genus $0$ part is the given flat F-manifold. If the flat F-manifold is homogeneous, then the associated family of F-CohFTs contains a subfamily of homogeneous F-CohFTs. However, unlike in the case of Frobenius manifolds and CohFTs, these homogeneous F-CohFTs can have different conformal dimensions, which are determined by the properties of a certain metric associated to the flat F-manifold.

math.AG↗

arXiv2022

Integrable systems, Nijenhuis geometry and Lauricella bi-flat structures

Combining the construction of integrable systems of hydrodynamic type starting from the Frölicher-Nijenhuis bicomplex $(d,d_L)$ associated with a (1,1)-tensor field $L$ with vanishing Nijenhuis torsion with the construction of flat structures starting from integrable systems of hydrodynamic type we define multi-parameter families of bi-flat structures $(\nabla,e,\circ,\nabla^*,*,E)$ associated with Frölicher-Nijenhuis bicomplexes. We call these structures Lauricella bi-flat structures since in the n-dimensional semisimple case (n-1) flat coordinates of r are Lauricella functions.

math.DG↗

arXiv2022

Weakly nonlocal Poisson brackets: tools, examples, computations

We implement an algorithm for the computation of Schouten bracket of weakly nonlocal Hamiltonian operators in three different computer algebra systems: Maple, Reduce and Mathematica. This class of Hamiltonian operators encompass almost all the examples coming from the theory of (1+1)-integrable evolutionary PDEs

math-ph↗

arXiv2022

Regular non-semisimple Dubrovin-Frobenius manifolds

We study regular non-semisimple Dubrovin-Frobenius manifolds in dimensions 2,3,4. We focus on the case where the Jordan canonical form of the operator of multiplication by the Euler vector field has a single Jordan block. Our results rely on the existence of special local coordinates introduced in [4] for regular flat F-manifolds with Euler vector field. In such coordinates the invariant metric of the Dubrovin-Frobenius manifold takes a special form which is the starting point of our construction.

math.DG↗

arXiv2021

A Dubrovin-Frobenius manifold structure of NLS type on the orbit space of $B_n$

Generalizing a construction presented in [3], we show that the orbit space of $B_2$ less the image of coordinate lines under the quotient map is equipped with two Dubrovin-Frobenius manifold structures which are related respectively to the defocusing and the focusing nonlinear Schrödinger (NLS) equations. Motivated by this example, we study the case of $B_n$ and we show that the defocusing case can be generalized to arbitrary $n$ leading to a Dubrovin-Frobenius manifold structure on the orbit space of the group. The construction is based on the existence of a non-degenerate and non-constant invariant bilinear form that plays the role of the Euclidean metric in the Dubrovin-Saito standard setting. Up to $n=4$ the prepotentials we get coincide with those associated with constrained KP equations discussed in [20].

math.DG↗

arXiv2021

Riemannian F-manifolds, bi-flat F-manifolds, and flat pencils of metrics

In this paper we study relations between various natural structures on F-manifolds. In particular, given an arbitrary Riemannian F-manifold we present a construction of a canonical flat F-manifold associated to it. We also describe a construction of a canonical homogeneous Riemannian F-manifold associated to an arbitrary exact homogeneous flat pencil of metrics satisfying a certain non-degeneracy assumption. In the last part of the paper we construct Legendre transformations for Riemannian F-manifolds.

math.DG↗

arXiv2020

Flat F-manifolds, F-CohFTs, and integrable hierarchies

We define the double ramification hierarchy associated to an F-cohomological field theory and use this construction to prove that the principal hierarchy of any semisimple (homogeneous) flat F-manifold possesses a (homogeneous) integrable dispersive deformation at all orders in the dispersion parameter. The proof is based on the reconstruction of an F-CohFT starting from a semisimple flat F-manifold and additional data in genus $1$, obtained in our previous work. Our construction of these dispersive deformations is quite explicit and we compute several examples. In particular, we provide a complete classification of rank $1$ hierarchies of DR type at the order $9$ approximation in the dispersion parameter and of homogeneous DR hierarchies associated with all $2$-dimensional homogeneous flat F-manifolds at genus $1$ approximation.

math-ph↗

arXiv2019

An exact study of phase transitions in mean field Potts models

We construct the exact partition function of the Potts model on a complete graph subject to external fields with linear and nematic type couplings. The partition function is obtained as a solution to a linear diffusion equation and the free energy, in the thermodynamic limit, follows from its semiclassical limit. Analysis of singularities of the equations of state reveals the occurrence of phase transitions of nematic type at not zero external fields and allows for an interpretation of the phase transitions in terms of shock dynamics in the space of thermodynamics variables. The approach is shown at work in the case of a q-state model for q=3 but the method generalises to arbitrary q.

math-ph↗

arXiv2019

Poisson pencils: reduction, exactness, and invariants

We study the invariants (in particular, the central invariants) of suitable Poisson pencils from the point of view of the theory of bi-Hamiltonian reduction, paying a particular attention to the case where the Poisson pencil is exact. We show that the exactness is preserved by the reduction. In the Drinfeld-Sokolov case, the same is true for the characteristic polynomial of the pencil, which plays a crucial role in the definition of the central invariants. We also discuss the bi-Hamiltonian structures of a generalized Drinfeld-Sokolov hierarchy and of the Camassa-Holm equation.

math-ph↗