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Semi-Free Actions with Manifold Orbit Spaces (2020)
Journal Article
Harvey, J., Kerin, M., & Shankar, K. (2020). Semi-Free Actions with Manifold Orbit Spaces. Documenta Mathematica, 25, 2085-2114. https://doi.org/10.25537/dm.2020v25.2085-2114

In this paper, we study smooth, semi-free actions on closed, smooth, simply connected manifolds, such that the orbit space is a smoothable manifold. We show that the only simply connected 5-manifolds admitting a smooth, semi-free circle action with f... Read More about Semi-Free Actions with Manifold Orbit Spaces.

Fake Lens Spaces and Non-Negative Sectional Curvature (2020)
Book Chapter
Goette, S., Kerin, M., & Shankar, K. (2020). Fake Lens Spaces and Non-Negative Sectional Curvature. In O. Dearricott, W. Tuschmann, Y. Nikolayevsky, T. Leistner, & D. Crowley (Eds.), Differential Geometry in the Large (285-290). Cambridge University Press. https://doi.org/10.1017/9781108884136.016

In this short note we observe the existence of free, isometric actions of finite cyclic groups on a family of 2-connected 7-manifolds with non-negative sectional curvature. This yields many new examples including fake, and possible exotic, lens space... Read More about Fake Lens Spaces and Non-Negative Sectional Curvature.

Highly connected 7-manifolds and non-negative sectional curvature (2020)
Journal Article
Goette, S., Kerin, M., & Shankar, K. (2020). Highly connected 7-manifolds and non-negative sectional curvature. Annals of Mathematics, 191(3), 829-892. https://doi.org/10.4007/annals.2020.191.3.3

In this article, a six-parameter family of highly connected 7-manifolds which admit an S O ( 3 ) -invariant metric of non-negative sectional curvature is constructed and the Eells-Kuiper invariant of each is computed. In particular, it follows that a... Read More about Highly connected 7-manifolds and non-negative sectional curvature.

Torus actions on rationally elliptic manifolds (2020)
Journal Article
Galaz-García, F., Kerin, M., & Radeschi, M. (2021). Torus actions on rationally elliptic manifolds. Mathematische Zeitschrift, 297, 197-221. https://doi.org/10.1007/s00209-020-02508-6

An upper bound is obtained on the rank of a torus which can act smoothly and effectively on a smooth, closed (simply connected) rationally elliptic manifold. In the maximal-rank case, the manifolds admitting such actions are classified up to equivari... Read More about Torus actions on rationally elliptic manifolds.

Torus Orbifolds, Slice-Maximal Torus Actions, and Rational Ellipticity (2017)
Journal Article
Galaz-García, F., Kerin, M., Radeschi, M., & Wiemeler, M. (2018). Torus Orbifolds, Slice-Maximal Torus Actions, and Rational Ellipticity. International Mathematics Research Notices, 2018(18), 5786-5822. https://doi.org/10.1093/imrn/rnx064

In this work, it is shown that a simply connected, rationally elliptic torus orbifold is equivariantly rationally homotopy equivalent to the quotient of a product of spheres by an almost-free, linear torus action, where this torus has rank equal to t... Read More about Torus Orbifolds, Slice-Maximal Torus Actions, and Rational Ellipticity.

Cohomogeneity-two torus actions on non-negatively curved manifolds of low dimension (2013)
Journal Article
Galaz-Garcia, F., & Kerin, M. (2014). Cohomogeneity-two torus actions on non-negatively curved manifolds of low dimension. Mathematische Zeitschrift, 276(1-2), 133-152. https://doi.org/10.1007/s00209-013-1190-5

Let Mn, n ∈ {4, 5, 6}, be a compact, simply connected n-manifold which admits some Riemannian metric with non-negative curvature and an isometry group of maximal possible rank. Then any smooth, effective action on Mn by a torus Tn−2 is equivariantly... Read More about Cohomogeneity-two torus actions on non-negatively curved manifolds of low dimension.

A note on totally geodesic embeddings of Eschenburg spaces into Bazaikin spaces (2012)
Journal Article
Kerin, M. (2013). A note on totally geodesic embeddings of Eschenburg spaces into Bazaikin spaces. Annals of Global Analysis and Geometry, 43(1), 63-73. https://doi.org/10.1007/s10455-012-9333-1

In this note it is shown that every 7-dimensional Eschenburg space can be totally geodesically embedded into infinitely many topologically distinct 13-dimensional Bazaikin spaces. Furthermore, examples are given which show that, under the known const... Read More about A note on totally geodesic embeddings of Eschenburg spaces into Bazaikin spaces.

Riemannian submersions from simple, compact Lie groups (2012)
Journal Article
Kerin, M., & Shankar, K. (2012). Riemannian submersions from simple, compact Lie groups. Münster journal of mathematics (Internet), 5(1), 25-40

In this paper we construct infinitely many examples of a Riemannian submersion from a simple, compact Lie group G with bi-invariant metric onto a smooth manifold that cannot be a quotient of G by a group action. This partially addresses a question of... Read More about Riemannian submersions from simple, compact Lie groups.

Some new examples with almost positive curvature (2011)
Journal Article
Kerin, M. (2011). Some new examples with almost positive curvature. Geometry & Topology, 15(1), 217-260. https://doi.org/10.2140/gt.2011.15.217

As a means to better understanding manifolds with positive curvature, there has been much recent interest in the study of nonnegatively curved manifolds which contain points at which all 2 –planes have positive curvature. We show that there are gener... Read More about Some new examples with almost positive curvature.

Almost positive curvature on the Gromoll-Meyer sphere (2008)
Journal Article
Eschenburg, J., & Kerin, M. (2008). Almost positive curvature on the Gromoll-Meyer sphere. Proceedings of the American Mathematical Society, 136(9), 3263-3270. https://doi.org/10.1090/s0002-9939-08-09429-x

Gromoll and Meyer have represented a certain exotic 7-sphere Σ7 as a biquotient of the Lie group G = Sp(2). We show for a 2-parameter family of left invariant metrics on G that the induced metric on Σ7 has strictly positive sectional curvature at all... Read More about Almost positive curvature on the Gromoll-Meyer sphere.