Abstract
On an almost complex manifold, a quasi-Kähler metric, with canonical connection in the c-projective class of a given minimal complex connection, is equivalent to a nondegenerate solution of the c-projectively invariant metrizability equation. For this overdetermined equation, replacing this maximal rank condition on solutions with a nondegeneracy condition on the prolonged system yields a strictly wider class of solutions with non-vanishing (generalized) scalar curvature. We study the geometries induced by this class of solutions. For each solution, the strict point-wise signature partitions the underlying manifold into strata, in a manner that generalizes the model, a certain Lie group orbit decomposition of \(\mathbb{C}\mathbb{P}^m\). We describe the smooth nature and geometric structure of each strata component, generalizing the geometries of the embedded orbits in the model. This includes a quasi-Kähler metric on the open strata components that becomes singular at the strata boundary. The closed strata inherit almost CR-structures and can be viewed as a c-projective infinity for the given quasi-Kähler metric.
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Notes
See the proof of Proposition 14 of [17] for a more details.
This term and the method of constructing a special boundary scale was first done the setting of projective differential geometry by Sam Porath in [43].
The prolongation connection is a natural modification of the tractor connection. See, e.g., [24] for a construction for general BGG operators.
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K. J. Flood gratefully acknowledges support from the Czech Science Foundation (GAČR) Grant 20-11473S and A. R. Gover gratefully acknowledges support from the Royal Society of New Zealand via Marsden Grants 16-UOA-051 and 19-UOA-008.
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Flood, K.J., Gover, A.R. Geometry of solutions to the c-projective metrizability equation. Annali di Matematica 202, 1343–1368 (2023). https://doi.org/10.1007/s10231-022-01283-x
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DOI: https://doi.org/10.1007/s10231-022-01283-x