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It is shown that the spheres S^(2n) (resp: S^k with k ≡ 1 mod 4)
can be given neither an indefinite metric of any signature (resp: of signature
(r, k − r) with 2 ≤ r ≤ k − 2) nor an almost paracomplex structure. Further
for every given Riemannian metric on an almost para-Hermitian manifold
with the associated 2-form φ one can construct an almost Hermitian structure
(under certain conditions, two different almost Hermitian structures)
whose associated 2-form(s) is φ.
Erdem, Sadettin. "Some Para-Hermitian Related Complex Structures and Non-existence of Semi-Riemannian Metric on Some Spheres." Serdica Mathematical Journal 25.1 (1999): 83-90. <http://eudml.org/doc/11506>.
@article{Erdem1999, abstract = {It is shown that the spheres S^(2n) (resp: S^k with k ≡ 1 mod 4)
can be given neither an indefinite metric of any signature (resp: of signature
(r, k − r) with 2 ≤ r ≤ k − 2) nor an almost paracomplex structure. Further
for every given Riemannian metric on an almost para-Hermitian manifold
with the associated 2-form φ one can construct an almost Hermitian structure
(under certain conditions, two different almost Hermitian structures)
whose associated 2-form(s) is φ.}, author = {Erdem, Sadettin}, journal = {Serdica Mathematical Journal}, keywords = {Hermitian; Para-Hermitian and Indefinite Metric; indefinite metric; para-Hermitian manifold; almost paracomplex structure}, language = {eng}, number = {1}, pages = {83-90}, publisher = {Institute of Mathematics and Informatics Bulgarian Academy of Sciences}, title = {Some Para-Hermitian Related Complex Structures and Non-existence of Semi-Riemannian Metric on Some Spheres}, url = {http://eudml.org/doc/11506}, volume = {25}, year = {1999}, }
TY - JOUR AU - Erdem, Sadettin TI - Some Para-Hermitian Related Complex Structures and Non-existence of Semi-Riemannian Metric on Some Spheres JO - Serdica Mathematical Journal PY - 1999 PB - Institute of Mathematics and Informatics Bulgarian Academy of Sciences VL - 25 IS - 1 SP - 83 EP - 90 AB - It is shown that the spheres S^(2n) (resp: S^k with k ≡ 1 mod 4)
can be given neither an indefinite metric of any signature (resp: of signature
(r, k − r) with 2 ≤ r ≤ k − 2) nor an almost paracomplex structure. Further
for every given Riemannian metric on an almost para-Hermitian manifold
with the associated 2-form φ one can construct an almost Hermitian structure
(under certain conditions, two different almost Hermitian structures)
whose associated 2-form(s) is φ. LA - eng KW - Hermitian; Para-Hermitian and Indefinite Metric; indefinite metric; para-Hermitian manifold; almost paracomplex structure UR - http://eudml.org/doc/11506 ER -