scholarly journals The Godbillon-Vey invariant as topological vorticity compression and obstruction to steady flow in ideal fluids

Author(s):  
Thomas Machon

If the vorticity field of an ideal fluid is tangent to a foliation, additional conservation laws arise. For a class of zero-helicity vorticity fields, the Godbillon-Vey (GV) invariant of foliations is defined and is shown to be an invariant purely of the vorticity, becoming a higher-order helicity-type invariant of the flow. GV ≠ 0 gives both a global topological obstruction to steady flow and, in a particular form, a local obstruction. GV is interpreted as helical compression and stretching of vortex lines. Examples are given where the value of GV is determined by a set of distinguished closed vortex lines.

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 878
Author(s):  
Alexei Cheviakov ◽  
Denys Dutykh ◽  
Aidar Assylbekuly

We investigate a family of higher-order Benjamin–Bona–Mahony-type equations, which appeared in the course of study towards finding a Galilei-invariant, energy-preserving long wave equation. We perform local symmetry and conservation laws classification for this family of Partial Differential Equations (PDEs). The analysis reveals that this family includes a special equation which admits additional, higher-order local symmetries and conservation laws. We compute its solitary waves and simulate their collisions. The numerical simulations show that their collision is elastic, which is an indication of its S−integrability. This particular PDE turns out to be a rescaled version of the celebrated Camassa–Holm equation, which confirms its integrability.


2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Atakan Hilmi Fırat

Abstract We begin developing tools to compute off-shell string amplitudes with the recently proposed hyperbolic string vertices of Costello and Zwiebach. Exploiting the relation between a boundary value problem for Liouville’s equation and a monodromy problem for a Fuchsian equation, we construct the local coordinates around the punctures for the generalized hyperbolic three-string vertex and investigate their various limits. This vertex corresponds to the general pants diagram with three boundary geodesics of unequal lengths. We derive the conservation laws associated with such vertex and perform sample computations. We note the relevance of our construction to the calculations of the higher-order string vertices using the pants decomposition of hyperbolic Riemann surfaces.


1970 ◽  
Vol 4 (4) ◽  
pp. 469-475 ◽  
Author(s):  
Alexander P. Stone

1985 ◽  
Vol 21 (10) ◽  
pp. 1035-1045 ◽  
Author(s):  
R. Kienzler ◽  
A. Golebiewska-Herrmann

1965 ◽  
Vol 20 (5) ◽  
pp. 649-655 ◽  
Author(s):  
G. Braunss

It is supposed that there exists a system O′ (intrinsic system) in which the field equation for a spin ½ representation has the simple form γµ ∂Ψ′/∂ϰμ′=0. This system is related to the physical system (in which all measurements are performed) by an affine connection which is induced by a certain group of local transformations. The investigation given here deals with the group of local four-dimensional complex orthogonal transformations. Subjecting ψ' to such a transformation Ω one gets with ψ' (x′) = Ω (x) ψ (x) the following equation γλ ∂Ψ/∂xλ+γλ Ω-1 ∂Ω/∂xλ ψ=0. The interaction term splits up into a vector and a pseudovector part: γλ Ω-1 ∂Ω/∂xλ ≡ γλ Vλ+γλ γ5 Ρλ. The special cases of real local orthogonal (LORENTZ-) transformations (ξλμ= - ξμλ; ξkl real, ξ4l imaginary; ψ → χ) and special complex local orthogonal transformations (ηλμ=- ημλ; ηkl imaginary, η4l real; ψ → φ) are first separately considered. It is required that Vλ and Pλ are to be built up from the fundamental covariants of the field. In order that certain conservation laws hold at least approximately, the following assumptions are made:Im{Vk}=±k2 ɸ̅γkφ, Re {V4}=±k2γ4φ, Im {Pk} = ± l2 χ̅ γk γ5 χ, Re {P4}= ±l2χ̅γ4γ5χ together with the symmetry conditions for the transformation parameters, ξλ[μυ] ≡ 0, η〈λμ,υ〉 ≡ 0, which can be fulfilled by setting, for example, ξλμ,υ = π[λπμ,υ],ηλμ = ϑ[λ,μ]. The remaining parts of Vλ and Ρλ, which are determined by these relations, are of higher order and can be assumed to describe weaker interactions. Neglecting these terms one obtains the following set of equations:(a) γλ ∂χ/∂xλ±k2γλ(ɸ̅γλφ) χ±l2γλγ5(χ̅γλγ5χ) χ≈0(b) γλ ∂χ/∂xλ±k2γλ(ɸ̅γλφ) φ±l2γλγ5(χ̅γλγ5χ) φ≈0Since the pseudovector coupling possesses a greater symmetry, it is assumed that χ represents the baryon and φ the lepton states. Within the approximation, which holds with (a) and (b), it follows the conservation of χ̅γλχand ɸ̅γλφ resp. (conservation of electric charge) and χ̅γλγ5χ and ɸ̅ γ·λγ5φ resp. (conservation of baryonic and leptonic charge resp.). These conservation laws are exact only if the mentioned terms of higher order are neglected; this is equivalent to a strict “local” conservation as can be shown. As to the isospin it is proposed to replace one of its components by a bounded state, i. e. a mixture of χ- and φ-states which would lead in the case of the neutron for example to the components of the /?β-decay. Due to the relations ± k2 ɸ̅γλφ = ¼ηλρ,ρ +O(η2) and ηλu = ϑ[λμ], and in agreement with the reality conditions, it is possible to connect the parameters ϑλ with the electromagnetic field Aλ by setting ϑλ= 8 iAλ. Taking into consideration terms of higher order this would lead to a type of nonlinear electrodynamics.


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