## Circle actions and scalar curvature

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**368**(2016), 2939-2966 Request permission

## Abstract:

We construct metrics of positive scalar curvature on manifolds with circle actions. One of our main results is that there exist $S^1$-invariant metrics of positive scalar curvature on every $S^1$-manifold which has a fixed point component of codimension $2$. As a consequence we can prove that there are non-invariant metrics of positive scalar curvature on many manifolds with circle actions. Results from equivariant bordism allow us to show that there is an invariant metric of positive scalar curvature on the connected sum of two copies of a simply connected semi-free $S^1$-manifold $M$ of dimension at least six provided that $M$ is not $\text {spin}$ or that $M$ is $\text {spin}$ and the $S^1$-action is of odd type. If $M$ is spin and the $S^1$-action of even type, then there is a $k>0$ such that the equivariant connected sum of $2^k$ copies of $M$ admits an invariant metric of positive scalar curvature if and only if a generalized $\hat {A}$-genus of $M/S^1$ vanishes.## References

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## Additional Information

**Michael Wiemeler**- Affiliation: Institut für Mathematik, Universität Augsburg, D-86135 Augsburg, Germany
- MR Author ID: 962657
- Email: michael.wiemeler@math.uni-augsburg.de
- Received by editor(s): March 27, 2014
- Received by editor(s) in revised form: December 16, 2014
- Published electronically: October 5, 2015
- © Copyright 2015 American Mathematical Society
- Journal: Trans. Amer. Math. Soc.
**368**(2016), 2939-2966 - MSC (2010): Primary 53C20, 57S15
- DOI: https://doi.org/10.1090/tran/6666
- MathSciNet review: 3449263