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Bochner's theorem (Riemannian geometry)

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is naturally identified with the vector space of Killing vector fields, it follows that the isometry group is zero-dimensional. Bochner's theorem then follows from the fact that the isometry group of a closed Riemannian manifold is compact.
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cannot have a local maximum. In particular, on a closed Riemannian manifold of negative Ricci curvature, every Killing vector field is identically zero. Since the isometry group of a complete Riemannian manifold is a
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has a local maximum, then it must be identically zero in a neighborhood. Since Killing vector fields on connected manifolds are uniquely determined from their value and derivative at a single point, it follows that
358:{\displaystyle {\frac {1}{2}}\Delta \langle X,X\rangle =\langle \nabla X,\nabla X\rangle -\nabla _{X}\operatorname {div} X+\langle X,\operatorname {div} ({\mathcal {L}}_{X}g)\rangle -\operatorname {Ric} (X,X).} 577: 93: 378: 62:
The theorem is a corollary of Bochner's more fundamental result which says that on any connected Riemannian manifold of negative Ricci curvature, the length of a nonzero
1179: 896: 817: 1198: 741:{\displaystyle \nabla ^{p}\nabla _{p}X_{i}=-\nabla _{i}\nabla ^{p}X_{p}+\nabla ^{p}(\nabla _{i}X_{p}+\nabla _{p}X_{i})-R_{ip}X^{p}.} 1172: 809: 17: 186:{\displaystyle \Delta X=-\nabla (\operatorname {div} X)+\operatorname {div} ({\mathcal {L}}_{X}g)-\operatorname {Ric} (X,\cdot )} 84: 1113: 1078: 1028: 1203: 925: 1165: 1108:. Classical Topics in Mathematics. Vol. 6 (New expanded ed.). Beijing: Higher Education Press. pp. 30–32. 985: 938: 464:{\displaystyle {\frac {1}{2}}\Delta \langle X,X\rangle =\langle \nabla X,\nabla X\rangle -\operatorname {Ric} (X,X).} 1153: 478:. However, on a Riemannian metric of negative Ricci curvature, the right-hand side is strictly positive wherever 876: 1008: 474:
In the case of a Riemannian metric, the left-hand side is nonpositive at any local maximum of the length of
858: 774: 930:. Interscience Tracts in Pure and Applied Mathematics. Vol. 15. Reprinted in 1996. New York–London: 931: 868: 1061:. Applied Mathematical Sciences. Vol. 116 (Second edition of 1996 original ed.). New York: 500: 1145: 968: 1123: 1088: 1038: 995: 948: 886: 838: 63: 39: 1096: 1046: 956: 846: 8: 1062: 1012: 964: 917: 43: 540: 27:
Isometry group of a compact Riemannian manifold with negative Ricci curvature is finite
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Partial differential equations II. Qualitative studies of linear equations
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Boothby, William M. (1954). "Book Review: Curvature and Betti numbers".
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Bochner's result on Killing vector fields is an application of the
976:. Ergebnisse der Mathematik und ihrer Grenzgebiete. Vol. 70. 1137: 200:
on a pseudo-Riemannian manifold. As a consequence, there is
1011:. Vol. 171 (Third edition of 1998 original ed.). 580: 381: 209: 96: 750: 516: 740: 463: 357: 185: 1190: 916: 867:. Annals of Mathematics Studies. Vol. 32. 780: 562: 546: 506: 1106:The Bochner technique in differential geometry 970:Transformation groups in differential geometry 967:(1972). "Isometries of Riemannian Manifolds". 372:is a Killing vector field, this simplifies to 1173: 897:Bulletin of the American Mathematical Society 818:Bulletin of the American Mathematical Society 528: 431: 413: 407: 395: 325: 287: 259: 241: 235: 223: 927:Foundations of differential geometry. Vol I 853: 574:In an alternative notation, this says that 1180: 1166: 963: 522: 1002: 784: 768: 550: 510: 893: 804: 14: 1191: 1053: 788: 756: 83:as follows. 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Index

Bochner–Yano theorem
mathematics
Salomon Bochner
Killing vector field
Riemannian manifold
Ricci curvature
isometry group
Killing vector field
Lie group
Lie algebra
maximum principle
Ricci commutation identities
Kobayashi & Nomizu 1963
Petersen 2016
Kobayashi 1972
Wu 2017
Kobayashi & Nomizu 1963
Petersen 2016
Kobayashi & Nomizu 1963
Taylor 2011
Petersen 2016
Kobayashi & Nomizu 1963
Petersen 2016
Taylor 2011
Bochner, S.
"Vector fields and Ricci curvature"
Bulletin of the American Mathematical Society
doi
10.1090/S0002-9904-1946-08647-4
MR

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