On the integral cohomology ring of toric orbifolds and singular toric varieties
Algebraic and Geometric Topology, Tome 17 (2017) no. 6, pp. 3779-3810

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We examine the integral cohomology rings of certain families of 2n–dimensional orbifolds X that are equipped with a well-behaved action of the n–dimensional real torus. These orbifolds arise from two distinct but closely related combinatorial sources, namely from characteristic pairs (Q,λ), where Q is a simple convex n–polytope and λ a labeling of its facets, and from n–dimensional fans Σ. In the literature, they are referred as toric orbifolds and singular toric varieties, respectively. Our first main result provides combinatorial conditions on (Q,λ) or on Σ which ensure that the integral cohomology groups H∗(X) of the associated orbifolds are concentrated in even degrees. Our second main result assumes these conditions to be true, and expresses the graded ring H∗(X) as a quotient of an algebra of polynomials that satisfy an integrality condition arising from the underlying combinatorial data. Also, we compute several examples.

DOI : 10.2140/agt.2017.17.3779
Classification : 14M25, 55N91, 57R18, 13F55, 52B11
Keywords: toric orbifold, quasitoric orbifold, toric variety, lens space, equivariant cohomology, Stanley–Reisner ring, piecewise polynomial

Bahri, Anthony 1 ; Sarkar, Soumen 2 ; Song, Jongbaek 3

1 Department of Mathematics, Rider University, Lawrenceville, NJ, United States
2 Department of Mathematics, Indian Institute of Technology Madras, Chennai, India
3 Department of Mathematical Sciences, KAIST, Daejeon, South Korea
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Bahri, Anthony; Sarkar, Soumen; Song, Jongbaek. On the integral cohomology ring of toric orbifolds and singular toric varieties. Algebraic and Geometric Topology, Tome 17 (2017) no. 6, pp. 3779-3810. doi: 10.2140/agt.2017.17.3779

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