Výsledky vyhledávání - "Uwe Semmelmann"

Linear instability of Sasaki Einstein and nearly parallel G2 manifolds

Autor: Uwe Semmelmann, Changliang Wang, M. Y.-K. Wang

Publikováno v: International Journal of Mathematics. 33

In this paper, we study the stability problem for the Einstein metrics on Sasaki Einstein and on complete nearly parallel [Formula: see text] manifolds. In the Sasaki case we show linear instability if the second Betti number is positive. Similarly,

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_________::10894eff0c73cf14b89267f7f50a188b
https://doi.org/10.1142/s0129167x22500422

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Generalized vector cross products and Killing forms on negatively curved manifolds

Autor: M. L. Barberis, Uwe Semmelmann, Andrei Moroianu

Publikováno v: Geometriae Dedicata. 205:113-127

Motivated by the study of Killing forms on compact Riemannian manifolds of negative sectional curvature, we introduce the notion of generalized vector cross products on $\mathbb{R}^n$ and give their classification. Using previous results about Killin

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::94205dca172ea4b0e5a36df4d68fb6d6
https://doi.org/10.1007/s10711-019-00467-9

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Deformations of nearly $G_2$-structures

Autor: Paul-Andi Nagy, Uwe Semmelmann

We describe the second order obstruction to deformation for nearly $G_2$ structures on compact manifolds. Building on work of B.Alexandrov and U.Semmelmann this allows proving rigidity under deformation for the proper nearly $G_2$ structure on the Al

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::aa879750c26130de9afb93a8d83f1fbe
http://arxiv.org/abs/2007.01657

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On the linear stability of nearly Kähler 6-manifolds

Autor: Changliang Wang, McKenzie Y. Wang, Uwe Semmelmann

Publikováno v: Annals of Global Analysis and Geometry

We show that a strict, nearly Kähler 6-manifold with either second or third Betti number nonzero is linearly unstable with respect to the $$\nu $$ν-entropy of Perelman and hence is dynamically unstable for the Ricci flow.

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::136548937ff67c6fa6e10a8ed5d945bb
https://hdl.handle.net/21.11116/0000-0005-F8B5-721.11116/0000-0005-F8B7-5

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Stability of Compact Symmetric Spaces

Autor: Uwe Semmelmann, Gregor Weingart

In this article we study the stability problem for the Einstein-Hilbert functional on compact symmetric spaces following and completing the seminal work of Koiso on the subject. We classify in detail the irreducible representations of simple Lie alge

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An Obata-type characterisation of Calabi metrics on line bundles

Autor: Nicolas Ginoux, Georges Habib, Mihaela Pilca, Uwe Semmelmann

Publikováno v: North-Western European Journal of Mathematics
North-Western European Journal of Mathematics, Laboratoires de Mathématiques du Nord-Pas-de-Calais, In press, 6, pp.119-136
HAL

International audience; We characterise those complete Kähler manifolds supporting a nonconstant real-valued function with critical points whose Hessian is nonnegative, complex linear, has pointwise two eigenvalues and whose gradient is a Hessian-ei

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=dedup_wf_001::2376f86d1de6dcc746530b05b4c3b178
https://hal.archives-ouvertes.fr/hal-02483865

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Conformal Killing forms on nearly Kähler manifolds

Autor: Uwe Semmelmann, Antonio Martínez Naveira

Publikováno v: Differential Geometry and its Applications. 70:101628

We study conformal Killing forms on compact 6-dimensional nearly Kahler manifolds. Our main result concerns forms of degree 3. Here we give a classification showing that all conformal Killing 3-forms are linear combinations of dω and its Hodge dual

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_________::324238b571cf367afa58b9410b6436e8
https://doi.org/10.1016/j.difgeo.2020.101628

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The kernel of the Rarita-Schwinger operator on Riemannian spin manifolds

Autor: Uwe Semmelmann, Yasushi Homma

We study the Rarita-Schwinger operator on compact Riemannian spin manifolds. In particular, we find examples of compact Einstein manifolds with positive scalar curvature where the Rarita-Schwinger operator has a non-trivial kernel. For positive quate

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