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Register a new userClassifying closed 2-orbifolds with Euler characteristics
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We determine the extent to which the collection of $Gamma$-Euler-Satake characteristics classify closed 2-orbifolds. In particular, we show that the closed, connected, effective, orientable 2-orbifolds are classified by the collection of $Gamma$-Euler-Satake characteristics corresponding to free or free abelian $Gamma$ and are not classified by those corresponding to any finite collection of finitely generated discrete groups. Similarly, we show that such a classification is not possible for non-orientable 2-orbifolds and any collection of $Gamma$, nor for noneffective 2-orbifolds. As a corollary, we generate families of orbifolds with the same $Gamma$-Euler-Satake characteristics in arbitrary dimensions for any finite collection of $Gamma$; this is used to demonstrate that the $Gamma$-Euler-Satake characteristics each constitute new invariants of orbifolds.
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We show that on every compact Riemannian 2-orbifold there exist infinitely many closed geodesics of positive length.
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