The positive scalar curvature cobordism category

Abstract

We prove that many spaces of positive scalar curvature metrics have the homotopy type of infinite loop spaces. Our result in particular applies to the path component of the round metric inside ${\mathcal{R}}^{+}(S^d)$ if $d\ge 6$. To achieve that goal, we study the cobordism category of manifolds with positive scalar curvature. Under suitable connectivity conditions, we can identify the homotopy fibre of the forgetful map from the psc cobordism category to the ordinary cobordism category with a delooping of spaces of psc metrics. This uses a version of Quillen's Theorem B and instances of the Gromov--Lawson surgery theorem. We extend some of the surgery arguments by Galatius and the second named author to the psc setting to pass between different connectivity conditions. Segal's theory of $\Gamma$-spaces is then used to construct the claimed infinite loop space structures. The cobordism category viewpoint also illuminates the action of diffeomorphism groups on spaces of psc metrics. We show that under mild hypotheses on the manifold, the action map from the diffeomorphism group to the homotopy automorphisms of the spaces of psc metrics factors through the Madsen--Tillmann spectrum. This implies a strong rigidity theorem for the action map when the manifold has trivial rational Pontrjagin classes. A delooped version of the Atiyah--Singer index theorem proved by the first named author is used to moreover show that the secondary index invariant to real $K$-theory is an infinite loop map. These ideas also give a new proof of the main result of our previous work with Botvinnik.

arXiv commentv2 98 pages. Accepted version, to appear in Duke Math. J; v3 Appended corrigendum

References in corpus (16)

• Monoids of moduli spaces of manifolds
• Infinite loop spaces and positive scalar curvature
• Semi-simplicial spaces
• The space of metrics of positive scalar curvature
• The Gromov-Lawson-Chernysh surgery theorem
• Codimension two index obstructions to positive scalar curvature
• Generalised Miller-Morita-Mumford classes for block bundles and topological bundles
• Homotopy groups of the moduli space of metrics of positive scalar curvature
• Infinite loop spaces and positive scalar curvature in the presence of a fundamental group
• Elliptic regularity for Dirac operators on families of noncompact manifolds
• Twisted Spin cobordism and positive scalar curvature
• The action of the mapping class group on metrics of positive scalar curvature
• On the infinite loop space structure of the cobordism category
• On the homotopy type of the space ${\mathcal{R}}^{+}(M)$
• An Additivity theorem for cobordism categories
• Cobordism Categories and Parametrized Morse Theory

Cited by in corpus (9)

• Band width estimates via the Dirac operator
• On the topology of moduli spaces of non-negatively curved Riemannian metrics
• An Additivity theorem for cobordism categories
• H-Space structures on spaces of metrics of positive scalar curvature
• The Disc-structure space
• The classifying space of the one-dimensional bordism category and a cobordism model for TC of spaces
• Homotopy invariance of the space of metrics with positive scalar curvature on manifolds with singularities
• Positive $(p,n)$-intermediate scalar curvature and cobordism
• Some rational homology computations for diffeomorphisms of odd-dimensional manifolds