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Search: MSC category 53C26 ( Hyper-Kahler and quaternionic Kahler geometry, special'' geometry )

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1. CJM 2012 (vol 65 pp. 757)

Delanoë, Philippe; Rouvière, François
 Positively Curved Riemannian Locally Symmetric Spaces are Positively Squared Distance Curved The squared distance curvature is a kind of two-point curvature the sign of which turned out crucial for the smoothness of optimal transportation maps on Riemannian manifolds. Positivity properties of that new curvature have been established recently for all the simply connected compact rank one symmetric spaces, except the Cayley plane. Direct proofs were given for the sphere, an indirect one via the Hopf fibrations) for the complex and quaternionic projective spaces. Here, we present a direct proof of a property implying all the preceding ones, valid on every positively curved Riemannian locally symmetric space. Keywords:symmetric spaces, rank one, positive curvature, almost-positive $c$-curvatureCategories:53C35, 53C21, 53C26, 49N60

2. CJM 2010 (vol 62 pp. 1264)

Chen, Jingyi; Fraser, Ailana
 Holomorphic variations of minimal disks with boundary on a Lagrangian surface Let $L$ be an oriented Lagrangian submanifold in an $n$-dimensional KÃ¤hler manifold~$M$. Let $u \colon D \to M$ be a minimal immersion from a disk $D$ with $u(\partial D) \subset L$ such that $u(D)$ meets $L$ orthogonally along $u(\partial D)$. Then the real dimension of the space of admissible holomorphic variations is at least $n+\mu(E,F)$, where $\mu(E,F)$ is a boundary Maslov index; the minimal disk is holomorphic if there exist $n$ admissible holomorphic variations that are linearly independent over $\mathbb{R}$ at some point $p \in \partial D$; if $M = \mathbb{C}P^n$ and $u$ intersects $L$ positively, then $u$ is holomorphic if it is stable, and its Morse index is at least $n+\mu(E,F)$ if $u$ is unstable. Categories:58E12, 53C21, 53C26

3. CJM 2005 (vol 57 pp. 1012)

Karigiannis, Spiro
 Deformations of $G_2$ and $\Spin(7)$ Structures We consider some deformations of $G_2$-structures on $7$-manifolds. We discover a canonical way to deform a $G_2$-structure by a vector field in which the associated metric gets twisted'' in some way by the vector cross product. We present a system of partial differential equations for an unknown vector field $w$ whose solution would yield a manifold with holonomy $G_2$. Similarly we consider analogous constructions for $\Spin(7)$-structures on $8$-manifolds. Some of the results carry over directly, while others do not because of the increased complexity of the $\Spin(7)$ case. Keywords:$G_2 \Spin(7)$, holonomy, metrics, cross productCategories:53C26, 53C29