Journal of Algebraic Geometry

Journal of Algebraic Geometry

Online ISSN 1534-7486; Print ISSN 1056-3911



Pointed trees of projective spaces

Authors: L. Chen, A. Gibney and D. Krashen
Journal: J. Algebraic Geom. 18 (2009), 477-509
Published electronically: November 19, 2008
MathSciNet review: 2496455
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Abstract | References | Additional Information

Abstract: We introduce a smooth projective variety $ T_{d,n}$ which compactifies the space of configurations of $ n$ distinct points on affine $ d$-space modulo translation and homothety. The points in the boundary correspond to $ n$-pointed stable rooted trees of $ d$-dimensional projective spaces, which for $ d = 1$, are $ (n+1)$-pointed stable rational curves. In particular, $ T_{1,n}$ is isomorphic to $ \overline{M}_{0,n+1}$, the moduli space of such curves. The variety $ T_{d,n}$ shares many properties with $ \overline{M}_{0,n+1}$. For example, as we prove, the boundary is a smooth normal crossings divisor whose components are products of $ T_{d,i}$ for $ i < n$, and it has an inductive construction analogous to but differing from Keel's for $ \overline{M}_{0,n+1}$. This can be used to describe its Chow groups and Chow motive generalizing

[Trans. Amer. Math. Soc. 330 (1992), 545-574]. It also allows us to compute its Poincaré polynomials, giving an alternative to the description implicit in

[Progr. Math., vol. 129, Birkhäuser, 1995, pp. 401-417]. We give a presentation of the Chow rings of $ T_{d,n}$, exhibit explicit dual bases for the dimension $ 1$ and codimension $ 1$ cycles. The variety $ T_{d,n}$ is embedded in the Fulton-MacPherson spaces $ X[n]$ for any smooth variety $ X$, and we use this connection in a number of ways. In particular we give a family of ample divisors on $ T_{d,n}$, and an inductive presentation of the Chow motive of $ X[n]$. This also gives an inductive presentation of the Chow groups of $ X[n]$ analogous to Keel's presentation for $ \overline{M}_{0,n+1}$, solving a problem posed by Fulton and MacPherson.

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Additional Information

L. Chen
Affiliation: Department of Mathematics, Ohio State University, Columbus, Ohio 43210
Address at time of publication: Department of Mathematics and Statistics, Swarthmore College, 500 College Avenue, Swarthmore, Pennsylvania 19081

A. Gibney
Affiliation: Department of Mathematics, University of Pennsylvania, Philadelphia, Pennsylvania 19104
Address at time of publication: Department of Mathematics, University of Georgia, Athens, Georgia 30602

D. Krashen
Affiliation: Department of Mathematics, Yale University, New Haven, Connecticut
Address at time of publication: Department of Mathematics, University of Georgia, Athens, Georgia 30602

Received by editor(s): March 1, 2007
Received by editor(s) in revised form: June 12, 2007
Published electronically: November 19, 2008
Additional Notes: The authors were supported during this work by the National Science Foundation under agreements DMS-0432701, DMS-0509319, and DMS-0111298, respectively.

American Mathematical Society