Completions of Period Mappings: Progress Report
COMPLETIONS OF PERIOD MAPPINGS: PROGRESS REPORT MARK GREEN, PHILLIP GRIFFITHS, AND COLLEEN ROBLES Abstract. We give an informal, expository account of a project to construct completions of period maps. 1. Introduction The purpose of this this paper is to give an expository overview, with examples to illus- trate some of the main points, of recent work [GGR21b] to construct \maximal" completions of period mappings. This work is part of an ongoing project, including [GGLR20, GGR21a], to study the global properties of period mappings at infinity. 1.1. Completions of period mappings. We consider triples (B; Z; Φ) consisting of a smooth projective variety B and a reduced normal crossing divisor Z whose complement B = BnZ has a variation of (pure) polarized Hodge structure p ~ F ⊂ V B ×π (B) V (1.1a) 1 B inducing a period map (1.1b) Φ : B ! ΓnD: arXiv:2106.04691v1 [math.AG] 8 Jun 2021 Here D is a period domain parameterizing pure, weight n, Q{polarized Hodge structures on the vector space V , and π1(B) Γ ⊂ Aut(V; Q) is the monodromy representation. Without loss of generality, Φ : B ! ΓnD is proper [Gri70a]. Let } = Φ(B) Date: June 10, 2021. 2010 Mathematics Subject Classification. 14D07, 32G20, 32S35, 58A14. Key words and phrases. period map, variation of (mixed) Hodge structure. Robles is partially supported by NSF DMS 1611939, 1906352. 1 2 GREEN, GRIFFITHS, AND ROBLES denote the image. The goal is to construct both a projective completion } of } and a surjective extension Φe : B ! } of the period map. We propose two such completions T B Φ }T (1.2) ΦS }S : The completion ΦT : B ! }T is maximal, in the sense that it encodes all the Hodge- theoretic information associated with the triple (B; Z; Φ).
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