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Classification of Homogeneous Third Order

Differential-Geometric Poisson Brackets

E.V. Ferapontov, M.V. Pavlov, G.V. Potemin, R. Vitolo

UK-Russia-Italian Collaboration

17.10.2013

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 1 / 17

First Order Differential-Geometric Poisson Brackets

First order differential-geometric Poisson brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂x + bijk (u(x))ukx ]δ(x − x ′)

satisfy the skew-symmetry and Jacobi identity iff g ij (u) is a

symmetric nondegenerate tensor and bijk (u) = −g isΓjsk , where Γ

jsk is

a Levi-Civita connection, while the metric gij (u) is flat.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 2 / 17

First Order Differential-Geometric Poisson Brackets

First order differential-geometric Poisson brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂x + bijk (u(x))ukx ]δ(x − x ′)

satisfy the skew-symmetry and Jacobi identity iff g ij (u) is a

symmetric nondegenerate tensor and bijk (u) = −g isΓjsk , where Γ

jsk is

a Levi-Civita connection, while the metric gij (u) is flat.

Corresponding Hamiltonian systems are

uit = [g ij∂x − g isΓjsku

kx ]

δH

δuj,

where the Hamiltonian functional H =∫

h(u,ux ,uxx ,uxxx , ...)dx .

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 2 / 17

First Order Differential-Geometric Poisson Brackets

First order differential-geometric Poisson brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂x + bijk (u(x))ukx ]δ(x − x ′)

satisfy the skew-symmetry and Jacobi identity iff g ij (u) is a

symmetric nondegenerate tensor and bijk (u) = −g isΓjsk , where Γ

jsk is

a Levi-Civita connection, while the metric gij (u) is flat.

Corresponding Hamiltonian systems are

uit = [g ij∂x − g isΓjsku

kx ]

δH

δuj,

where the Hamiltonian functional H =∫

h(u,ux ,uxx ,uxxx , ...)dx .

In a particular case H =∫

h(u)dx , we have N componenthydrodynamic type system

uit = (∇i∇jh)ujx .

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 2 / 17

Third Differential-Geometric Poisson Brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂3x + bijk (u(x))ukx ∂2x

+(c ijk (u(x))ukxx + c ijkm(u(x))u

kx u

mx )∂x

+d ijk (u(x))u

kxxx + d ij

km(u(x))ukx u

mxx + d ij

kmn(u(x))ukx u

mx u

nx ]δ(x − x ′).

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 3 / 17

Third Differential-Geometric Poisson Brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂3x + bijk (u(x))ukx ∂2x

+(c ijk (u(x))ukxx + c ijkm(u(x))u

kx u

mx )∂x

+d ijk (u(x))u

kxxx + d ij

km(u(x))ukx u

mxx + d ij

kmn(u(x))ukx u

mx u

nx ]δ(x − x ′).

In special coordinate system d ijk (a) = 0, d ij

km(a) = 0, d ijkmn(a) = 0. Then

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 3 / 17

Third Differential-Geometric Poisson Brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂3x + bijk (u(x))ukx ∂2x

+(c ijk (u(x))ukxx + c ijkm(u(x))u

kx u

mx )∂x

+d ijk (u(x))u

kxxx + d ij

km(u(x))ukx u

mxx + d ij

kmn(u(x))ukx u

mx u

nx ]δ(x − x ′).

In special coordinate system d ijk (a) = 0, d ij

km(a) = 0, d ijkmn(a) = 0. Then

{ai (x), aj (x ′)} = ∂x [gij (a(x))∂x + bijk (a(x))u

kx ]δ

′(x − x ′).

satisfy the skew-symmetry and Jacobi identity iff

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 3 / 17

Third Differential-Geometric Poisson Brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂3x + bijk (u(x))ukx ∂2x

+(c ijk (u(x))ukxx + c ijkm(u(x))u

kx u

mx )∂x

+d ijk (u(x))u

kxxx + d ij

km(u(x))ukx u

mxx + d ij

kmn(u(x))ukx u

mx u

nx ]δ(x − x ′).

In special coordinate system d ijk (a) = 0, d ij

km(a) = 0, d ijkmn(a) = 0. Then

{ai (x), aj (x ′)} = ∂x [gij (a(x))∂x + bijk (a(x))u

kx ]δ

′(x − x ′).

satisfy the skew-symmetry and Jacobi identity iff

gmk,n + gkn,m + gmn,k = 0,

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n),

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 3 / 17

Third Differential-Geometric Poisson Brackets

{ui (x), uj (x ′)} = [g ij (u(x))∂3x + bijk (u(x))ukx ∂2x

+(c ijk (u(x))ukxx + c ijkm(u(x))u

kx u

mx )∂x

+d ijk (u(x))u

kxxx + d ij

km(u(x))ukx u

mxx + d ij

kmn(u(x))ukx u

mx u

nx ]δ(x − x ′).

In special coordinate system d ijk (a) = 0, d ij

km(a) = 0, d ijkmn(a) = 0. Then

{ai (x), aj (x ′)} = ∂x [gij (a(x))∂x + bijk (a(x))u

kx ]δ

′(x − x ′).

satisfy the skew-symmetry and Jacobi identity iff

gmk,n + gkn,m + gmn,k = 0,

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n),

where cnkm = 13 (gmn,k − gkn,m) and cijk = giqgjpb

pqk .

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 3 / 17

Metric. Nonlinear System

gmk,n + gkn,m + gmn,k = 0,

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n).

This system has a solution in the form

gik = g(0)ik + g

(1)ikma

m + g(2)ikmna

man.

The nonlinear part

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n)

can be parameterized in the form

gik = φβγψiβψkγ,

where ψiβ = ψiβmam + ξ iβ and ψiβk = −ψkβi .

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 4 / 17

Metric. Nonlinear System

gmk,n + gkn,m + gmn,k = 0,

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n).

This system has a solution in the form

gik = g(0)ik + g

(1)ikma

m + g(2)ikmna

man.

The nonlinear part

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n)

can be parameterized in the form

gik = φβγψiβψkγ,

where ψiβ = ψiβmam + ξ iβ and ψiβk = −ψkβi .Lie Algebras.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 4 / 17

Metric. Nonlinear System

The linear partgmk,n + gkn,m + gmn,k = 0

can be solved by virtue of the Monge parameterization:

ds2 = gik(a)daidak = ~dT Q̂~d ,

where ~d = (da1, da2, ..., daN , a1da2 − a2da1, a2da3 − a3da2, ...) andQ̂ is a constant nondegenerate symmetric matrix.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 5 / 17

Metric. Nonlinear System

The linear partgmk,n + gkn,m + gmn,k = 0

can be solved by virtue of the Monge parameterization:

ds2 = gik(a)daidak = ~dT Q̂~d ,

where ~d = (da1, da2, ..., daN , a1da2 − a2da1, a2da3 − a3da2, ...) andQ̂ is a constant nondegenerate symmetric matrix.

Passive Form.gmk,n + gkn,m + gmn,k = 0,

gmn,kl =1

9gpq(gqk,ngpl ,m − gqk,ngpm,l + gqk,mgpl ,n − gqk,mgpn,l

+gqn,kgpm,l − gqn,kgpl ,m + gqm,kgpn,l − gqm,kgpl ,n).

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 5 / 17

Particular Case

Theorem: In the particular case cijk = 0 (three distinct indices), a generalsolution of the above nonlinear system is parameterized by a solepolynomial function G of degree 4 such that

gkk = −2G,kk , gkm = G,km, ckkm = −ckmk = G,kkm, k 6= m,

while all other connection coefficients cijk = 0.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 6 / 17

Particular Case

Theorem: In the particular case cijk = 0 (three distinct indices), a generalsolution of the above nonlinear system is parameterized by a solepolynomial function G of degree 4 such that

gkk = −2G,kk , gkm = G,km, ckkm = −ckmk = G,kkm, k 6= m,

while all other connection coefficients cijk = 0.

This leads to

gmm = − ∑p 6=m

Rmp(ap)2 − 2 ∑

p 6=m

Hmpap +Dm,

gkm = Rkmakam +Hkma

k +Hmkam + Fkm, k 6= m,

where Rkm = Rmk ,Fkm = Fmk , Dk are constants, and

cmmk = −cmkm = Rkmak +Hmk , k 6= m.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 6 / 17

Two Component Case

Theorem: only two metrics in 2-component case:

g(1)ik =

(

1− (a2)2 1+ a1a2

1+ a1a2 1− (a1)2

)

, g(2)ik =

(

−2a2 a1

a1 0

)

.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 7 / 17

Three Component Case

Using the ansatz cijk = 0 we are able to reduce the nonlinear system to:

R12F12 = H12H21, F13R13 = H13H31, F23R23 = H23H32,

D1R12R13 +H212R13 +H2

13R12 = 0,

D2R12R23 +H221R23 +H2

23R12 = 0,

D3R13R23 +H231R23 +H2

32R13 = 0.

In the generic case Rij 6= 0 we obtain the three-parameter family of metrics

gik =

−(a2 + β2)2 − (a3)2 a1(a2 + β2) a3(a1 + β1)

a1(a2 + β2) −(a1)2 − (a3 + β3)2 a2(a3 + β3)

a3(a1 + β1) a2(a3 + β3) −(a1 + β1)2 − (a2)2

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 8 / 17

Three Component Case

Using the ansatz cijk = 0 we are able to reduce the nonlinear system to:

R12F12 = H12H21, F13R13 = H13H31, F23R23 = H23H32,

D1R12R13 +H212R13 +H2

13R12 = 0,

D2R12R23 +H221R23 +H2

23R12 = 0,

D3R13R23 +H231R23 +H2

32R13 = 0.

In the generic case Rij 6= 0 we obtain the three-parameter family of metrics

gik =

−(a2 + β2)2 − (a3)2 a1(a2 + β2) a3(a1 + β1)

a1(a2 + β2) −(a1)2 − (a3 + β3)2 a2(a3 + β3)

a3(a1 + β1) a2(a3 + β3) −(a1 + β1)2 − (a2)2

The particular cases

1 R12 = 0, R13 6= 0, R23 6= 0,2 R12 = 0, R13 = 0, R23 6= 0,3 R12 = 0, R13 = 0, R23 = 0,

were solved separately, obtaining a complete classification of 53 metrics.EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 8 / 17

WDVV Associativity Equations

In three component case, WDVV associativity equations reduce to thesingle equation

fttt = f 2xxt − fxxx fxtt ,

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 9 / 17

WDVV Associativity Equations

In three component case, WDVV associativity equations reduce to thesingle equation

fttt = f 2xxt − fxxx fxtt ,

which can be written as the hydrodynamic type system

at = bx , bt = cx , ct = (b2 − ac)x ,

where a = fxxx , b = fxxt , c = fxtt .

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 9 / 17

WDVV Associativity Equations

In three component case, WDVV associativity equations reduce to thesingle equation

fttt = f 2xxt − fxxx fxtt ,

which can be written as the hydrodynamic type system

at = bx , bt = cx , ct = (b2 − ac)x ,

where a = fxxx , b = fxxt , c = fxtt .

This system is bi-Hamiltonian, i.e.

abc

t

= J0δH1 = J1δH0,

where

J0 =

− 32D

12Da Db

12aD

12 (bD +Db) 3

2cD + cxbD 3

2Dc − cx (b2 − ac)D +D(b2 − ac)

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 9 / 17

WDVV Associativity Equations

and

J1 =

0 0 D3

0 D3 −D2aDD3 −DaD2 D2bD +DbD2 +DaDaD

.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 10 / 17

WDVV Associativity Equations

and

J1 =

0 0 D3

0 D3 −D2aDD3 −DaD2 D2bD +DbD2 +DaDaD

.

Here H1 =∫

cdx ,H0 = − 12a(D

−1b)2 − (D−1b)(D−1c).

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 10 / 17

Lorentzian Metric

The third order Hamiltonian structure is associated with the action

S =1

2

(f 2xt fxxx + fxt ftt)dxdt.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 11 / 17

Riemann Curvature Tensor

The Riemann tensor of curvature has the form

Rjikl = gjsRsikl = gjs [∂kΓs

il − ∂lΓsik + Γs

knΓnil − Γs

lnΓnik ],

where

Γijk =

1

2g im(gmj ,k + gmk,j − gjk,m).

However, taking into account

gmk,n + gkn,m + gmn,k = 0,

we obtainΓijk = −g imgjk,m.

ThenRjikl = gik,jl − gil ,jk + g sm(gik,mgjl ,s − gil ,mgjk,s).

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 12 / 17

References

beamericonarticleA.V. Balandin, G.V. Potemin,On non-degenerate differential-geometric Poisson brackets of thirdorder, Russian Mathematical Surveys 56 No. 5 (2001) 976-977.

beamericonarticleP.W. Doyle,Differential geometric Poisson bivectors in one space variable, J.Math. Phys. 34 No. 4 (1993) 1314-1338.

beamericonarticleB.A. Dubrovin and S.P. Novikov,Hamiltonian formalism of one-dimensional systems of hydrodynamictype and the Bogolyubov-Whitham averaging method, Soviet Math.Dokl., 27 (1983) 665–669.

beamericonarticleE.V. Ferapontov,On integrability of 3× 3 semi-Hamiltonian systems of hydrodynamictype which do not possess Riemann invariants, Physica D 63 (1993)50-70.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 13 / 17

References

beamericonarticleE.V. Ferapontov,On the matrix Hopf equation and integrable Hamiltonian systems ofhydrodynamic type which do not possess Riemann invariants, Phys.lett. A 179 (1993) 391-397.

beamericonarticleE.V. Ferapontov,Several conjectures and results in the theory of integrable Hamiltoniansystems of hydrodynamic type, which do not possess Riemanninvariants, Teor. Math. Phys., 99 No. 2 (1994) 257-262.

beamericonarticleE.V. Ferapontov,Dupin hypersurfaces and integrable Hamiltonian systems ofhydrodynamic type, which do not possess Riemann invariants, Diff.Geom. Appl., 5 (1995) 121-152.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 14 / 17

References

beamericonarticleE.V. Ferapontov,Isoparametric hypersurfaces in spheres, integrable nondiagonalizablesystems of hydrodynamic type, and N-wave systems, Diff. Geom.Appl., 5 (1995) 335-369.

beamericonarticleE.V. Ferapontov, C.A.P. Galvao, O. Mokhov, Y. Nutku,Bi-Hamiltonian structure of equations of associativity in 2-dtopological field theory, Comm. Math. Phys. 186 (1997) 649-669.

beamericonarticleE.V. Ferapontov, O.I. Mokhov,Equations of associativity of two-dimensional topological field theoryas integrable Hamiltonian nondiagonalisable systems of hydrodynamictype, Func. Anal. Appl. 30 No. 3 (1996) 195-203.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 15 / 17

References

beamericonarticleE.V. Ferapontov, R. Sharipov,On the first order conservation laws of hydrodynamic type systems,Teor. Math. Phys. 108 No. 1 (1996) 937-952.

beamericonarticleO.I. Mokhov,Symplectic and Poisson structures on loop spaces of smoothmanifolds, and integrable systems, Russian Math. Surveys 53 No. 3(1998) 85–192.

beamericonarticleS.P. Novikov,The geometry of conservative systems of hydrodynamic type. Themethod of averaging for field-theoretical systems, Russian Math.Surveys 40 No. 4 (1985) 85–98.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 16 / 17

References

beamericonarticleG.V. Potemin,On Poisson brackets of differential-geometric type, Dokl. Akad. NaukSSSR, 286 (1986) 39–42; Soviet Math. Dokl. 33 (1986) 30–33.

beamericonarticleG.V. Potemin,On third-order Poisson brackets of differential geometry, Russ. Math.Surv. 52 (1997) 617-618.

beamericonarticleG.V. Potemin,Some aspects of differential geometry and algebraic geometry in thetheory of solitons. PhD Thesis, Moscow, Moscow State University(1991) 99 pages.

EVF, MVP, GVP, RV (Italy, Russia, UK) Poisson Brackets 17.10.2013 17 / 17

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