TY  - JOUR
A1  - Bär, Christian
T1  - Geometrically formal 4-manifolds with nonnegative sectional curvature
T2  - Communications in analysis and geometry
N2  - A Riemannian manifold is called geometrically formal if the wedge product of any two harmonic forms is again harmonic. We classify geometrically formal compact 4-manifolds with nonnegative sectional curvature. If the sectional curvature is strictly positive, the manifold must be homeomorphic to S-4 or diffeomorphic to CP2.
 This conclusion stills holds true if the sectional curvature is strictly positive and we relax the condition of geometric formality to the requirement that the length of harmonic 2-forms is not too nonconstant. In particular, the Hopf conjecture on S-2 x S-2 holds in this class of manifolds.
Y1  - 2015
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/38811
SN  - 1019-8385
SN  - 1944-9992
VL  - 23
IS  - 3
SP  - 479
EP  - 497
PB  - International Press of Boston
CY  - Somerville
ER  -