On the pluricanonical maps of varieties of intermediate Kodaira dimension

Jiang, Xiaodong

doi:10.1007/s00208-012-0869-y

Cited by 12 publications

(7 citation statements)

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“…The relevance of the above conjecture is well illustrated for instance by a result due to X. Jiang, who proved recently in [12] that Conjecture EbS 1.1 implies a uniformity statement for the Iitaka fibration of any variety of positive Kodaira dimension under the assumption that the fibres have a good minimal model. Moreover Todorov and Todorov-Xu prove some unconditional uniformity results for the Iitaka fibration of varieties of Kodaira dimension at most 2 and Kodaira codimension 1 (Todorov [22,Theorem 1.2]) and 2 (Todorov and Xu [23,Theorem 1.2]).…”

Section: Introductionmentioning

confidence: 91%

Inductive Approach to Effective b-Semiampleness

Floris

2012

International Mathematics Research Notices

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Abstract. An lc-trivial fibration is the data of a pair (X, B) and a fibration such that (K X + B)| F is torsion where F is the general fibre. For such a fibration we have an equality K X + B + 1/r(ϕ) = f * (K Z + B Z + M Z ) where B Z is the discriminant of f , M Z is the moduli part and ϕ is a rational function. It has been conjectured by Prokhorov and Shokurov that there exists an integer m = m(r, dim F ) such that mM Z ′ is base-point-free on some birational model Z ′ of Z. In this work we reduce this conjecture to the case where the base Z has dimension one. Moreover in the case where M Z ≡ 0 we prove the existence of an integer m, that depends only on the middle Betti number of a canonical covering of the fibre, such that mM Z ∼ 0. IntroductionThe canonical bundle formula is a tool for studying the properties of the canonical bundle of a variety X, such that there exists a fibration f : X → Z, in terms of the properties of the canonical bundle of Z, of the singularities of the fibration and of the birational variation of the fibres of f .More precisely we consider a pair (X, B) such that there exists an lc-trivial fibration f : (X, B) → Z, that is a fibration such that (K X + B)| F is a torsion divisor, where F is a general fibre (see Section 2 for a complete definition). Then we can writewhere ϕ is a rational function and r is the minimum integer such that r(K X + B)| F ∼ 0. The divisor B Z is called the discriminant and it is defined in terms of some log-canonical thresholds with respect to the pair (X, B). Precisely we have B Z = (1 − γ p )p whereThe divisor M Z , called the moduli part, is a Q-Cartier divisor and it is nef on some birational modification of Z by [2, Theorem 0.2]. The moduli part should be related to the birational variation of the fibres of f . This is true for instance in the case of elliptic fibrations. Indeed, if f : X → Z is an elliptic fibration, we have Kodaira's canonical bundle formulaDate: July 30, 2017.where j : Z → P 1 = M 1 is the application induced by f to the moduli space of elliptic curves. In particular M Z is semiample.In [20] Prokhorov and Shokurov state the following conjecture (in our statement we specify the dimension of the base).EbS(k) 1.1 (Effective b-Semiampleness, Conjecture 7.13.3, [20]). There exists an integer number m = m(d, r) such that for any lc-trivial fibration f : (X, B) → Z with dimension of the generic fibre F equal to d, dimension of Z equal to k and Cartier index of (F, B| F ) equal to r there exists a birational morphism ν : Z ′ → Z such that mM Z ′ is base point free.The relevance of the above conjecture is well illustrated for instance by a result due to X. It is worth noticing that the proofs of semiampleness in these cases use the existence of a moduli space for the fibres.The main goal of this work is to develop an inductive approach to the conjecture EbS. Our first result is the following. Theorem 1.2. EbS(1) implies EbS(k).An inductive approach on the dimension of the base as in Theorem 1.2 allows us to prove a result of effective semiam...

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Section: Introductionmentioning

confidence: 91%

Inductive Approach to Effective b-Semiampleness

Floris

2012

International Mathematics Research Notices

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“…Even if the previous question seems very restrictive, using the argument in [Jia12] and Theorem 4.1, it implies the uniformity of the Iitaka fibration when the variation is maximal. See [DiC11] for more details.…”

Section: Effective Birationalitymentioning

confidence: 99%

On Fujita’s log spectrum conjecture

Cerbo

2015

Math. Ann.

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“…Various low dimensional cases of Conjecture 1.2 are known (see [Kol94,Ale94,Jia13,Tod10,TX09]). In arbitrary dimension, we also have an affirmative answer in the log general type case (cf.…”

Section: Introductionmentioning

confidence: 99%