## Journal of the Mathematical Society of Japan

### An index formula for a bundle homomorphism of the tangent bundle into a vector bundle of the same rank, and its applications

#### Abstract

In a previous work, the authors introduced the notion of ‘coherent tangent bundle’, which is useful for giving a treatment of singularities of smooth maps without ambient spaces. Two different types of Gauss–Bonnet formulas on coherent tangent bundles on $2$-dimensional manifolds were proven, and several applications to surface theory were given.

Let $M^n$ ($n\ge 2$) be an oriented compact $n$-manifold without boundary and $TM^n$ its tangent bundle. Let $\mathcal{E}$ be a vector bundle of rank $n$ over $M^n$, and $\phi:TM^n\to \mathcal{E}$ an oriented vector bundle homomorphism. In this paper, we show that one of these two Gauss–Bonnet formulas can be generalized to an index formula for the bundle homomorphism $\phi$ under the assumption that $\phi$ admits only certain kinds of generic singularities.

We shall give several applications to hypersurface theory. Moreover, as an application for intrinsic geometry, we also give a characterization of the class of positive semi-definite metrics (called Kossowski metrics) which can be realized as the induced metrics of the coherent tangent bundles.

#### Article information

Source
J. Math. Soc. Japan, Volume 69, Number 1 (2017), 417-457.

Dates
First available in Project Euclid: 18 January 2017

Permanent link to this document
https://projecteuclid.org/euclid.jmsj/1484730031

Digital Object Identifier
doi:10.2969/jmsj/06910417

Mathematical Reviews number (MathSciNet)
MR3597560

Zentralblatt MATH identifier
1372.57039

Subjects
Primary: 57R45: Singularities of differentiable mappings
Secondary: 53A05: Surfaces in Euclidean space

#### Citation

SAJI, Kentaro; UMEHARA, Masaaki; YAMADA, Kotaro. An index formula for a bundle homomorphism of the tangent bundle into a vector bundle of the same rank, and its applications. J. Math. Soc. Japan 69 (2017), no. 1, 417--457. doi:10.2969/jmsj/06910417. https://projecteuclid.org/euclid.jmsj/1484730031

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