Comment on the Bäcklund transformations for the chiral field equation

It will be shown that the three different Bäcklund transformations for the static axially symmetric chiral field equation, given by Levi and Ragnisco, are related by a simple transformation due to the existence of an invariance symmetry of the solutions of the equation.     

Multi-kink solutions and soliton fission and fusion of Sharma-Tasso-Olver equation

From the Levi spectral problem, we obtain two basic Darboux transformations of the Sharma-Tasso-Olver equation. Then from the trivial seed solution, we obtain multi-kink solutions and soliton fission and fusion solutions of this equation.     

The Cohomology of the Variational Bicomplex Invariant under the Symmetry Algebra of the Potential Kadomtsev-Petviashvili Equation

Abstract

The variational bicomplex of forms invariant under the symmetry algebra of the potential Kadomtsev-Petviashvili equation is described and the cohomology of the associated Euler-Lagrange complex is computed. The results are applied to a characterization problem of the Kadomtsev-Petviashvili equation by its symmetry algebra originally posed by David, Levi, and Winternitz.     

A Higher Order (2+1)-Dimensional Korteweg-de Vries Equation and Its Exact Solitary Wave Solutions

The (2+l)-dimensional Korteweg-de Vries (KdV) equation proposed recently by Levi is extended to a higher order (2+1)-dimensional KdV equation from water wave dynamics when considering surface tension. Its exact and explicit solitary wave solutions can be obtained by relating it to the higher order KdV equation.     

Conservation Laws and Symmetries of the Levi Equation

The conservation laws of the Levi equation are presented. Two types of symmetry of the Levi equation hierarchy are deduced, Further it is proved that these symmetries construct an infinite-dimensional Lie algebra.     

Multi-component Levi Hierarchy and Its Multi-component Integrable Coupling System

A simple 3M-dimensional loop algebra X is produced, whose commutation operation defined by us is as simple and straightforward as that in the loop algebra A1. It follows that a general scheme for generating multicomponent integrable hierarchy is proposed. By taking advantage of X, a new isospectral problem is established, and then by making use of the Tu scheme the well-known multi-component Levi hierarchy is obtained. Finally, an expanding loop algebra FM of the loop algebra X is presented, based on the FM, the multi-component integrable coupling system of the multi-component Levi hierarchy is worked out. The method in this paper can be applied to other nonlinear evolution equation hierarchies.     

Multi-component Levi Hierarchy and Its Multi-component Integrable Coupling System

A simple 3M-dimensional loop algebra X is produced, whose commutation operation defined by us is A1 as simple and straightforward as that in the loop algebra A1. It follows that a general scheme for generating multi-component integrable hierarchy is proposed. By taking advantage of X, a new isospectral problem is established, and then by making use of the Tu scheme the well-known multi-component Levi hierarchy is obtained. Finally, an expanding loop algebra FM of the loop algebra .X is presented, based on the FM, the multi-component integrable coupling system of the multi-component Levi hierarchy is worked out. The method in this paper can be applied to other nonlinear evolution equation hierarchies.     

Non-linear representations of inhomogeneous groups

We classify the analytic actions, having a fixed point, of the classical inhomogeneous groups, such that the linear part of this action restricted to a Levi factor is the natural action defining this Levi factor as a classical simple group.     

Multi-Soliton Solutions of the Levi Equations

The multisoliton solutions of the Levi equations are derived with the Hirota method and Wronskian technique respectively.     

Double Wronskian Solutions of Non-Isospectral Levi Equations

The double Wronskian solutions of the non-isospectral Levi equationsare derived through Wronskian technique.     

Integrable discrete autonomous quad-equations admitting,as generalized symmetries,known five-point differential-difference equations

In this paper we construct the autonomous quad-equations which admit as symmetries the five-point differential-difference equations belonging to known lists found by Garifullin, Yamilov and Levi. The obtained equations are classified up to autonomous point transformations and some simple non-autonomous transformations. We discuss our results in the framework of the known literature. There are among them a few new examples of both sine-Gordon and Liouville type equations.     

Classification of multidimensional spacetimes

We classify all eleven-dimensional spatially homogeneous spacetimes, which contain a seven-dimensional compact subspace and admit a simple-transitive group of isometry, by enumerating the real ten-dimensional Lie algebras which contain an n-dimensional (n⩾7) compact Lie subalgebra. The main result of this paper consists in giving a complete list of the distinct real ten-dimensional algebras which admit a non-trivial Levi decomposition. It is hoped that this investigation may be of some help in studying eleven-dimensional and ten-dimensional cosmologies which are considered in the context of Kaluza-Klein, supergravity and superstring theories.     

Conformal transformations in metric‐affine gravity and ghosts

Conformal transformations play a widespread role in gravity theories in regard to their cosmological and other implications. In the pure metric theory of gravity, conformal transformations change the frame to a new one wherein one obtains a conformal‐invariant scalar–tensor theory such that the scalar field, deriving from the conformal factor, is a ghost. In this work, conformal transformations and ghosts will be analyzed in the framework of the metric‐affine theory of gravity. Within this framework, metric and connection are independent variables, and, hence, transform independently under conformal transformations. It will be shown that, if affine connection is invariant under conformal transformations, then the scalar field of concern is a non‐ghost, non‐dynamical field. It is an auxiliary field at the classical level, and might develop a kinetic term at the quantum level. Alternatively, if connection transforms additively with a structure similar to yet more general than that of the Levi‐Civita connection, the resulting action describes the gravitational dynamics correctly, and, more importantly, the scalar field becomes a dynamical non‐ghost field. The equations of motion, for generic geometrical and matter‐sector variables, do not reduce connection to the Levi‐Civita connection, and, hence, independence of connection from metric is maintained. Therefore, metric‐affine gravity provides an arena in which ghosts arising from the conformal factor are avoided thanks to the independence of connection from the metric.     

Comparison of Various K̄N Partial Wave Analyses in the Region 0–1400 MeV/c

A comprehensive comparative study of the available K̄N partial wave analyses is made with a view to bring out their similarities and disagreements and to point towards those momentum regions that require particular attention in all future analyses. The multichannel nature of the K̄N scattering is discussed along with the presently available scattering cross-section data for various channels. The parametrization of the various partial wave analyses is discussed and their amplitudes calculated and compared under the set of conventions proposed by Levi Setti.     

Pre-symplectic algebroids and their applications

In this paper, we introduce the notion of a pre-symplectic algebroid and show that there is a one-to-one correspondence between pre-symplectic algebroids and symplectic Lie algebroids. This result is the geometric generalization of the relation between left-symmetric algebras and symplectic (Frobenius) Lie algebras. Although pre-symplectic algebroids are not left-symmetric algebroids, they still can be viewed as the underlying structures of symplectic Lie algebroids. Then we study exact pre-symplectic algebroids and show that they are classified by the third cohomology group of a left-symmetric algebroid. Finally, we study para-complex pre-symplectic algebroids. Associated with a para-complex pre-symplectic algebroid, there is a pseudo-Riemannian Lie algebroid. The multiplication in a para-complex pre-symplectic algebroid characterizes the restriction to the Lagrangian subalgebroids of the Levi–Civita connection in the corresponding pseudo-Riemannian Lie algebroid.     

A multidimensional extension of the Bianchi type-IX cosmology

A higher-dimensional homogeneous spacetime is investigated satisfying the vacuum Einstein equations. It is assumed that the algebra of Killing vectors L admits a non-trivial Levi decomposition L = N ⨴so(3), i.e. that the subalgebras N and so(3) do not commute. It is found that the model behaves in a non-chaotic way and cosmological dimensional reduction inevitably occurs. This model completes all the possible types within the class of higher-dimensional extensions of Bianchi type-IX cosmology.     

Gravity theory on Poisson manifold with R‐flux

A novel gravity theory based on Poisson Generalized Geometry is investigated. A gravity theory on a Poisson manifold equipped with a Riemannian metric is constructed from a contravariant version of the Levi‐Civita connection, which is based on the Lie algebroid of a Poisson manifold. Then, we show that in Poisson Generalized Geometry the R‐fluxes are consistently coupled with such a gravity. An R‐flux appears as a torsion of the corresponding connection in a similar way as an H‐flux which appears as a torsion of the connection formulated in the standard Generalized Geometry. We give an analogue of the Einstein‐Hilbert action coupled with an R‐flux, and show that it is invariant under both β‐diffeomorphisms and β‐gauge transformations.     

Re-analysis of the baryon mass spectrum using the quark shell model

Detailed numerical comparison of the baryon mass spectrum analysis of Jones, Levi Setti and Lasinski with that of Horgan has led to a deeper understanding of the formulae and techniques used in both analyses. In this light, we have re-analysed the baryon mass spectrum for the (70, 1^?)₁ and (56/70, 2⁺)₂ multiplets updated to include the most recent PDG data and have checked the results for the (70, 1^?)₁ using two independent computer programmes. The predicted spectra obtained are presented and the classification of the states is compared with that of a recent decay analysis by Hey, Litchfield and Cashmore.     

Hydrodynamic theory of forced dewetting

A prototypical problem in the study of wetting phenomena is that of a solid plunging into or being withdrawn from a liquid bath. In the latter, dewetting case, a critical speed exists above which a three-phase contact line is no longer sustainable and the solid can no longer remain dry. Instead, a liquid film is being deposited on the solid. Demonstrating this transition from a dry to a wetted solid to be of hydrodynamic origin, we provide the first theoretical explanation of a classical prediction due to Derjaguin and Levi: instability occurs when the outer, static meniscus approaches the shape corresponding to a perfectly wetting fluid. Our analysis investigates the conditions under which the highly curved contact line region can be matched to the static profile far away from it.     

Quadratic metric‐affine gravity

We consider spacetime to be a connected real 4‐manifold equipped with a Lorentzian metric and an affine connection. The 10 independent components of the (symmetric) metric tensor and the 64 connection coefficients are the unknowns of our theory. We introduce an action which is (purely) quadratic in curvature and study the resulting system of Euler–Lagrange equations. In the first part of the paper we look for Riemannian solutions, i.e. solutions whose connection is Levi‐Civita. We find two classes of Riemannian solutions: 1) Einstein spaces, and 2) spacetimes with pp‐wave metric of parallel Ricci curvature. We prove that for a generic quadratic action these are the only Riemannian solutions. In the second part of the paper we look for non‐Riemannian solutions. We define the notion of a “Weyl pseudoinstanton” (metric compatible spacetime whose curvature is purely of Weyl type) and prove that a Weyl pseudoinstanton is a solution of our field equations. Using the pseudoinstanton approach we construct explicitly a non‐Riemannian solution which is a wave of torsion in a spacetime with Minkowski metric. We discuss the possibility of using this non‐Riemannian solution as a mathematical model for the neutrino.