A connection between cut locus, Thom space and Morse–Bott functions
Algebraic and Geometric Topology, Tome 23 (2023) no. 9, pp. 4185-4233

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Associated to every closed, embedded submanifold N in a connected Riemannian manifold M, there is the distance function dN which measures the distance of a point in M from N. We analyze the square of this function and show that it is Morse–Bott on the complement of the cut locus Cu ⁡ (N) of N provided M is complete. Moreover, the gradient flow lines provide a deformation retraction of M − Cu ⁡ (N) to N. If M is a closed manifold, then we prove that the Thom space of the normal bundle of N is homeomorphic to M∕Cu ⁡ (N). We also discuss several interesting results which are either applications of these or related observations regarding the theory of cut locus. These results include, but are not limited to, a computation of the local homology of singular matrices, a classification of the homotopy type of the cut locus of a homology sphere inside a sphere, a deformation of the indefinite unitary group U(p,q) to U(p) × U(q) and a geometric deformation of GL ⁡ (n, ℝ) to O(n, ℝ) which is different from the Gram–Schmidt retraction.

DOI : 10.2140/agt.2023.23.4185
Keywords: cut locus, distance function, Morse–Bott function, Thom space

Basu, Somnath 1 ; Prasad, Sachchidanand 1

1 Department of Mathematics and Statistics, Indian Institute of Science Education and Research, Kolkata, India
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Basu, Somnath; Prasad, Sachchidanand. A connection between cut locus, Thom space and Morse–Bott functions. Algebraic and Geometric Topology, Tome 23 (2023) no. 9, pp. 4185-4233. doi: 10.2140/agt.2023.23.4185

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