Twistor Forms on Riemannian Products

We study twistor forms on products of compact Riemannian manifolds and show that they are defined by Killing forms on the factors. The main result of this note is a necessary step in the classification of compact Riemannian manifolds with non-generic holonomy carrying twistor forms.Comment: 5 page

The Weitzenb\"ock Machine

In this article we give a unified treatment of the construction of all possible Weitzenb\"ock formulas for all irreducible, non--symmetric holonomy groups. The resulting classification is two--fold, we construct explicitly a basis of the space of Weitzenb\"ock formulas on the one hand and characterize Weitzenb\"ock formulas as eigenvectors for an explicitly known matrix on the other. Both classifications allow us to find tailor--suit Weitzenb\"ock formulas for applications like eigenvalue estimates or Betti number estimates.Comment: 48 page

Conformal Killing forms on Riemannian manifolds

Conformal Killing forms are a natural generalization of conformal vector fields on Riemannian manifolds. They are defined as sections in the kernel of a conformally invariant first order differential operator. We show the existence of conformal Killing forms on nearly Kaehler and weak G_2-manifolds. Moreover, we give a complete description of special conformal Killing forms. A further result is a sharp upper bound on the dimension of the space of conformal Killing forms.Comment: 24 page

Infinitesimal Einstein Deformations of Nearly K\"ahler Metrics

It is well-known that every 6-dimensional strictly nearly K\"{a}hler manifold $(M,g,J)$ is Einstein with positive scalar curvature $scal>0$. Moreover, one can show that the space $E$ of co-closed primitive (1,1)-forms on $M$ is stable under the Laplace operator $\Delta$. Let $E(a)$ denote the $a$-eigenspace of the restriction of $\Delta$ to $E$. If $M$ is compact, we prove that the moduli space of infinitesimal Einstein deformations of the nearly K\"{a}hler metric $g$ is naturally isomorphic to the direct sum $E(scal/15)\oplus E(scal/5)\oplus E(2scal/5)$. It is known that the last summand is itself isomorphic with the moduli space of infinitesimal nearly K\"{a}hler deformations