Integral formulae for foliated manifolds with singularities Dedicated
Transkrypt
Integral formulae for foliated manifolds with singularities Dedicated
Integral formulae for foliated manifolds with singularities Dedicated to Professor A. A. Borisenko on his 70th birthday Pawel G. Walczak Katedra Geometrii, Uniwersytet Lódzki [email protected] Kharkiv, MAGT, September 12 – 16, 2016 Pawel G. Walczak Katedra Geometrii, Uniwersytet Lódzki [email protected] Integral formulae for foliated manifolds with singularities D 1. General setting M = a closed Riemannian manifold of dimension n + 1 Σ = a union of finitely many closed, pairwise disjoint submanifolds of codim ≥ k F = a codimension-1 foliation F everything smooth and oriented N = the positive oriented unit normal A = −∇N = the shape (Weingarten) operator (on T F) k1 , . . . kn = the principal curvatures = the eigenvalues of A σj = the j-th mean curvature = the j-th elementary symmetric function of ki ’s, j = 1, . . . n Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 2. General idea X = a “geometrically interesting” vector field on M r Σ f = div X calculated in terms of geometry (intrinsic/extrinsic curvatures etc.) Then Hölder Inequality + some calculations imply the following integral formula: Lemma If (k − 1)(p − 1) ≥ 1 and R M kX kp d vol < ∞, then Z f d vol = 0. (1) M Why interesting? Because Equation (1) implies, for example, obstructions for the existence of foliations with given geometric properties (geodesic, minimal, umbilical etc.) Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 3. First formula Theorem (G. Reeb, ∼ 1950 for Σ = ∅) Z σ1 = − div X and σ1 d vol = 0. (2) M if only k ≥ 2. Proof. Apply our Lemma to X = N. Corollary (P. W. 1984, G. Oshikiri 1997) If Σ = ∅, then: f = σ1 for some Riemannian metric g ⇐⇒ either f = 0 everywhere on M or f (x)f (y ) < 0 for suitable x, y ∈ M Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 4. On space forms Question How to get the following from our general setting? Theorem (Asimov, Brito - Langevin - Rosenberg, ∼ 1980) If M is of constant curvature, then Z σk d vol = ck , (3) M ck being a constant independent of F. Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 5. A bit of algebra B = (B1 , B2 , . . . , Bm ) – a sequence of quadratic n × n matrices (or, linear transformations of a given vector space) Definition Invariants σλ (B) are given by det(I + t1 B1 + . . . tm Bm ) = X σλ (B) · t λ , (4) λ λm . where λ = (λ1 , . . . , λm ) is a multiindex and t λ = t1λ1 · . . . · tm Definition For λ as above, kλk = λ1 + 2λ2 + . . . + λm . Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki (5) [email protected] Integral formulae for foliated manifolds with singularities D 6. On symmetric spaces Define: RN = R(·, N)N : T F → T F B2k = (−1)k k (2k)! RN , B2k+1 = (−1)k k (2k+1)! RN A Theorem (V. Rovenski and P. W., ∼ 2008, Math. Ann. 2012) If M is locally symmetric and Σ = ∅, then for any m > 0 one has Z X σλ (B) d vol = 0. (6) M kλk=m Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 7. On arbitrary manifolds, no singularities Tr – Newton transformations (of A : T F → T F): T0 = I , Tr = σr I − ATr −1 for 1 ≤ r ≤ n = dim M. (7) Calculating div Xr , where Xr = Tr (∇N N) + σr +1 N we obtain: Theorem (K. Andrzejewski and P. W., Ann. Glob. Anal. Geom. 2010) If Σ = ∅, then – for all r – Z X r M trF (R((−A)j−1 ∇N N)Tr −j ) − (r + 2)σr +2 j=1 + trF (R(N)Tr ) d vol, (8) where R(Z ) : T F 3 X 7→ R(X , Z )N ∈ T F. Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 8. On arbitrary manifolds, with singularities Theorem Assume that (i) a codimension one foliation F is defined on M r Σ, Σ being a union of finitely many, pairwise disjoint, closed submanifolds Si of codimensions ki ≥ k ≥ 2, (ii) the norm kAk of the Weingarten operator A of F is L(r +1)p -integrable on M for some r ∈ N and p > 1 such that (k − 1)(p − 1) ≥ 1, and (iii) the curvature κ = k∇N Nk of the 1-dimensional foliation by integral curves of the unit normal N of F is L(r +1)p -integrable. Then, equality (8) holds. Remark Both, Eqs. (6) and (8), imply (3). Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 9. Particular case: r = 2 Corollary (T. Nora, Thése, 1983, for Σ = ∅) If (k − 1)(p − 1) ≥ 1 and kAk, κ ∈ L3p then Z (2σ2 − Ric(N, N))d vol = 0. (9) M Corollary (R. Lanevgin, P.W., Geom. Ded., 2008, for Σ = 0) Under the above integrability assumptions, codimension-one foliations on manifolds of negative Ricci curvature are far from being umbilical: Z X (∃C > 0) (∀F) |ki − kj |n+1 ≥ C > 0. (10) M i<j Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D 10. Bibliography K. Andrzejewski and P. Walczak, The Newton transformation and new integral formulae for foliated manifolds, Ann. Glob. Anal. Geom. 37 (2010), 103 – 111. D. Asimov, Average gaussian curvature of leaves of foliations, Bull. Amer. Math. Soc. 84 (1978), 131 – 133. F. Brito, R. Langevin and H. Rosenberg, Intégrales de courbure sur les variétées feuilletées, J. Diff. Geom. 16, 19 – 50. T. Nora, Seconde forme fondamentale d’une application et d’un feuilletage, Thése, l’Univ. de Limoges, 1983. G. Reeb, Sur la courbure moyenne des variétés intégrales d’une équation de Pfaff, C. R. Acad. Sci. Paris 231, (1950), 101 – 102. V. Rovenski and P. Walczak, Integral formulae for foliated symmetric spaces, Math. Ann. 352 (2012), 223 – 237. Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D Thank You! Dziękuję! Cnacu6o! Cnacu6i! νχαριστ ω! Paweł G. Walczak Katedra Geometrii, Uniwersytet Łódzki [email protected] Integral formulae for foliated manifolds with singularities D