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Solvmanifolds with integrable and non-integrable G_2 structures

I. Agricola·S. Chiossi·A. Fino
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Abstract

We show that a 7-dimensional non-compact Ricci-flat Riemannian manifold with Riemannian holonomy G_2 can admit non-integrable G_2 structures of type R + S^2_0(R^7) + R^7 in the sense of Fernández and Gray. This relies on the construction of some G_2 solvmanifolds, whose Levi-Civita connection is known to give a parallel spinor, admitting a 2-parameter family of metric connections with non-zero skew-symmetric torsion that has parallel spinors as well. The family turns out to be a deformation of the Levi-Civita connection. This is in contrast with the case of compact scalar-flat Riemannian spin manifolds, where any metric connection with closed torsion admitting parallel spinors has to be torsion-free.

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I. Agricola, S. Chiossi, A. Fino. 2005-10-14. Solvmanifolds with integrable and non-integrable G_2 structures. https://arxiv.org/abs/math/0510300

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