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Holomorphic sections of line bundles vanishing along subvarieties Dan Coman, George Marinescu and Vi et-Anh Nguy en Department of Mathematics, Syracuse University Syracuse, NY 13244-1150, USA 2019 Taipei Conference on Complex Geometry


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Holomorphic sections of line bundles vanishing along subvarieties

Dan Coman, George Marinescu and Viˆ et-Anh Nguyˆ en

Department of Mathematics, Syracuse University Syracuse, NY 13244-1150, USA

2019 Taipei Conference on Complex Geometry Institute of Mathematics, Academia Sinica, Taipei, Taiwan December 15 - 19, 2019

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Plan of the talk:

  • 1. Preliminaries and notation
  • 2. Dimension of spaces of holomorphic sections

vanishing along subvarieties

  • 3. Envelopes of quasiplurisubharmonic functions

with poles along a divisor

  • 4. Convergence of Fubini-Study currents
  • 5. Zeros of random sequences of holomorphic sections

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  • 1. Preliminaries and notation

Pluripotential theory on compact complex manifolds X compact complex manifold, dim X = n, ω Hermitian form on X d = ∂ + ∂ , dc =

1 2πi (∂ − ∂) , ddc = i π ∂∂

ν(T, x) = Lelong number of a positive closed current T on X at x ∈ X ϕ : X → R ∪ {−∞} is called quasiplurisubharmonic (qpsh) if ϕ = u + χ , near each x ∈ X, where u is plurisubharmonic (psh) and χ is smooth. If α is a smooth real closed (1, 1)-form on X, we let PSH(X, α) = {ϕ : X → R ∪ {−∞} : ϕ qpsh, α + ddcϕ ≥ 0}.

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Lelong number of ϕ at x ∈ X: ν(ϕ, x) := ν(α + ddcϕ, x) = ν(u, x) {α}∂∂ := ∂∂-cohomology class of a smooth real closed (1, 1)-form α on X H1,1

∂∂ (X, R) := {{α}∂∂ : α smooth real closed (1, 1)-form on X}

Since X is compact, H1,1

∂∂ (X, R) is finite dimensional.

If X is a compact K¨ ahler manifold then, by the ∂∂-lemma, H1,1

∂∂ (X, R) = H1,1(X, R) .

Definition 1 A positive closed current T of bidegree (1, 1) is called a K¨ ahler current if T ≥ εω, ε > 0. A class {α}∂∂ is big if it contains a K¨ ahler current.

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If {α}∂∂ is big then, by Demailly’s regularization theorem, ∃ T ∈ {α}∂∂ K¨ ahler current with analytic singularities, i.e. T = α + ddcϕ ≥ ǫω, where ǫ > 0, ϕ = c log

  • N
  • j=1

|gj|2 + χ locally on X, with c > 0, χ a smooth function and gj holomorphic functions. Non-ample locus of {α}∂∂: NAmp

  • {α}∂∂
  • =

E+(T) : T ∈ {α}∂∂ K¨ ahler current

  • =

E+(T) : T ∈ {α}∂∂ K¨ ahler current with analytic singularities

  • ,

where E+(T) = {x ∈ X : ν(T, x) > 0}. Hence NAmp

  • {α}∂∂
  • is an analytic subset of X.

Boucksom: ∃ T ∈ {α}∂∂ K¨ ahler current with analytic singularities such that E+(T) = NAmp

  • {α}∂∂
  • .

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Plurisubharmonic (psh) functions and currents on analytic spaces Let X be an irreducible complex space, dim X = n Xreg := set of regular points of X, Xsing := set of singular points of X Call τ : U ⊂ X → G ⊂ CN a local embedding if U is open in X, G is open in CN, and τ : U → V is a biholomorphism, where V ⊂ G is a (closed) analytic subvariety. ϕ : X → [−∞, ∞) is (strictly) psh if for every x ∈ X there exist: τ : Ux ⊂ X → G ⊂ CN local embedding, and

  • ϕ : G → [−∞, ∞) (strictly) psh with ϕ|Ux =

ϕ ◦ τ. If ϕ can be chosen continuous (resp. smooth), then ϕ is called a continuous (resp. smooth) psh function.

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If τ : U ⊂ X → G ⊂ CN is a local embedding, then Ω∞

p,q(U) := τ ∗(Ω∞ p,q(G)), where τ ∗ : Ω∞ p,q(G) → Ω∞ p,q(U ∩ Xreg).

Dp,q(X) ⊂ Ω∞

p,q(X) is the space of C ∞ smooth (p, q)-forms with compact

  • support. The dual D′

p,q(X) of Dp,q(X) is the space of currents of

bidimension (p, q), or bidegree (n − p, n − q), on X. T (X) ⊂ D′

n−1,n−1(X) is the space of positive closed currents with local

psh potentials: T ∈ T (X) if for every x ∈ X there exist Ux ⊂ X (depending on T) and v psh on Ux such that T = ddcv on Ux ∩ Xreg. A K¨ ahler form on X is a current ω ∈ T (X) whose local potentials are smooth strictly psh functions.

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Singular Hermitian holomorphic line bundles X compact, irreducible, normal complex space, dim X = n π : L − → X holomorphic line bundle on X: X = Uα, Uα open, gαβ ∈ O∗

X(Uα ∩ Uβ) are the transition functions.

H0(X, L) = space of global holomorphic sections of L, dim H0(X, L) < ∞ Singular Hermitian metric h on L: {ϕα ∈ L1

loc(Uα, ωn)}α such that

ϕα = ϕβ + log |gαβ| on Uα ∩ Uβ, |eα|h = e−ϕα (eα local frame on Uα). The curvature current c1(L, h) ∈ D′

n−1,n−1(X) of h:

c1(L, h) = ddcϕα on Uα ∩ Xreg. If c1(L, h) ≥ 0 then ϕα is psh on Uα ∩ Xreg, hence on Uα (X is normal). So c1(L, h) ∈ T (X).

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  • 2. Dimension of spaces of holomorphic sections vanishing along

subvarieties X compact complex manifold, dim X = n, L → X holomorphic line bundle Lp := L⊗p, H0(X, Lp) = space of global holomorphic sections of Lp Siegel’s Lemma: ∃ C > 0 such that dim H0(X, Lp) ≤ Cpn for all p ≥ 1. A line bundle L is called big if lim sup

p→∞

1 pn dim H0(X, Lp) > 0. If L is big one can show that ∃ c > 0, p0 ≥ 1, such that dim H0(X, Lp) ≥ cpn for all p ≥ p0. Ji-Shiffman: L is big if and only if ∃ h singular Hermitian metric on L such that c1(L, h) is a K¨ ahler current.

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Setting: (A) X is a compact, irreducible, normal complex space, dim X = n, Xreg is the set of regular points of X, Xsing is the set of singular points of X. (B) L is a holomorphic line bundle on X. (C) Σ = (Σ1, . . . , Σℓ), Σj ⊂ Xsing, are distinct irreducible proper analytic subsets of X. (D) τ = (τ1, . . . , τℓ), τj ∈ (0, +∞), and τj > τk if Σj ⊂ Σk.

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Let: tj,p =

  • τjp

if τjp ∈ N ⌊τjp⌋ + 1 if τjp ∈ N , 1 ≤ j ≤ ℓ , p ≥ 1 . H0

0(X, Lp) = H0 0(X, Lp, Σ, τ) :=

  • S ∈ H0(X, Lp) : ord(S, Σj) ≥ tj,p
  • So S ∈ H0

0(X, Lp) vanishes to order at least τjp along Σj, 1 ≤ j ≤ ℓ.

Definition 2 We say that the triplet (L, Σ, τ) is big if lim sup

p→∞

1 pn dim H0

0(X, Lp) > 0.

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Characterization when X is a complex manifold and dim Σj = n − 1: Theorem 3 Let: X compact complex manifold, dim X = n, L holomorphic line bundle

  • n X, Σ = (Σ1, . . . , Σℓ), τ = (τ1, . . . , τℓ), where Σj are distinct irreducible

complex hypersurfaces in X, τj ∈ (0, +∞). The following are equivalent: (i) (L, Σ, τ) is big; (ii) There exists a singular Hermitian metric h on L such that c1(L, h) −

  • j=1

τj[Σj] is a K¨ ahler current on X, where [Σj] is the current of integration along Σj; (iii) ∃ c > 0, p0 ≥ 1, such that dim H0

0(X, Lp) ≥ cpn for all p ≥ p0.

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Proposition 4 Let X, Σ verify (A), (C). Then there exist a compact complex manifold X, dim X = n, and a surjective holomorphic map π : X → X, given as the composition of finitely many blow-ups with smooth center, such that: (i) ∃ Y ⊂ X analytic subset such that dim Y ≤ n − 2, Xsing ⊂ Y , Σj ⊂ Y if dim Σj ≤ n − 2, Y ⊂ Xsing ∪ ℓ

j=1 Σj, E = π−1(Y ) is a divisor in

X that has only normal crossings, and π : X \ E → X \ Y is a biholomorphism. (ii) There exist smooth complex hypersurfaces Σ1, . . . , Σℓ in X such that π( Σj) = Σj. If dim Σj = n − 1 then Σj is the final strict transform of Σj, and if dim Σj ≤ n − 2 then Σj is an irreducible component of E. (iii) If F → X is a holomorphic line bundle and S ∈ H0(X, F) then

  • rd(S, Σj) = ord(π⋆S,

Σj), for all j = 1, . . . , ℓ.

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Definition 5 If X, π, Σ := ( Σ1, . . . , Σℓ), verify the conclusions of Proposition 4, we say that ( X, π, Σ) is a divisorization of (X, Σ). Theorem 6 Let X, L, Σ, τ verify assumptions (A)-(D). The following are equivalent: (i) (L, Σ, τ) is big; (ii) ∀ ( X, π, Σ) divisorization of (X, Σ), ∃ h⋆ singular metric on π⋆L such that c1(π⋆L, h⋆) − ℓ

j=1 τj[

Σj] is a K¨ ahler current on X; (iii) Assertion (ii) holds for some divisorization ( X, π, Σ) of (X, Σ); (iv) ∃ c > 0, p0 ≥ 1, such that dim H0

0(X, Lp) ≥ cpn for all p ≥ p0.

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Theorem 6 follows directly from Theorem 3 since, by Proposition 4, H0

0(X, Lp, Σ, τ) ∼

= H0

0(

X, π⋆Lp, Σ, τ) , ∀ p ≥ 1. Theorem 6 has the following interesting corollary: Corollary 7 Let X, L, Σ, τ verify assumptions (A)-(D). Assume that dim Σj = n − 1 and let Σ′

j ⊂ Σj be distinct irreducible proper analytic subsets such that

Σ′

j ⊂ Xsing, j = 1, . . . , ℓ. For δ > 0 set

Σ′ = (Σ1, . . . , Σℓ, Σ′

1, . . . , Σ′ ℓ), τ ′ = (τ1, . . . , τℓ, τ1 + δ, . . . , τℓ + δ).

If (L, Σ, τ) is big, then (L, Σ′, τ ′) is big, for all δ > 0 sufficiently small.

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  • 3. Envelopes of qpsh functions with poles along a divisor

X compact complex manifold, dim X = n, ω Hermitian form on X, dist = distance on X induced by ω Σj ⊂ X irreducible complex hypersurfaces, τj > 0, where 1 ≤ j ≤ ℓ. Write Σ = (Σ1, . . . , Σℓ), τ = (τ1, . . . , τℓ), Let: α be a smooth closed real (1, 1)-form on X, gj smooth Hermitian metric on OX(Σj), sΣj be the canonical section of OX(Σj), 1 ≤ j ≤ ℓ, βj = c1(OX(Σj), gj) , θ = α −

  • j=1

τjβj , σj := |sΣj|gj . Lelong-Poincar´ e Formula: [Σj] = βj + ddc log σj L(X, α, Σ, τ) = {ψ ∈ PSH(X, α) : ν(ψ, x) ≥ τj, ∀ x ∈ Σj, 1 ≤ j ≤ ℓ}

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Given ϕ : X → R ∪ {−∞} we consider the following: A(X, α, Σ, τ, ϕ) = {ψ ∈ L(X, α, Σ, τ) : ψ ≤ ϕ on X} A′(X, α, Σ, τ, ϕ) = =

  • ψ′ ∈PSH(X, θ) : ψ′ ≤ ϕ −

  • j=1

τj log σj on X \

  • j=1

Σj

  • ϕeq = ϕeq,Σ,τ = sup{ψ : ψ ∈ A(X, α, Σ, τ, ϕ)}

= equilibrium envelope of (α, Σ, τ, ϕ) ϕreq = ϕreq,Σ,τ = sup{ψ′ : ψ′ ∈ A′(X, α, Σ, τ, ϕ)} = reduced equilibrium envelope of (α, Σ, τ, ϕ) Motivated by the notion of equilibrium metric associated to a Hermitian metric on a holomorphic line bundle (Berman, Ross-Witt Nystr¨

  • m).

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Proposition 8 Let X, Σ, τ, α, θ be as above, and let ϕ : X → R ∪ {−∞} be an upper semicontinuous function. Then the following hold: (i) PSH(X, θ) ∋ ψ′ → ψ := ψ′ + ℓ

j=1 τj log σj ∈ L(X, α, Σ, τ) is well

defined and bijective. (ii) ∃ C > 0 such that supX ψ′ ≤ supX ϕ + C, ∀ ψ′ ∈ A′(X, α, Σ, τ, ϕ). (iii) A(X, α, Σ, τ, ϕ) = ∅ if and only if A′(X, α, Σ, τ, ϕ) = ∅. In this case, ϕreq ∈ A′(X, α, Σ, τ, ϕ), ϕeq ∈ A(X, α, Σ, τ, ϕ), ϕeq = ϕreq +

  • j=1

τj log σj. (iv) If ϕ is bounded and there exists a bounded θ-psh function, then ϕreq is bounded on X. (v) If PSH(X, θ) = ∅ and ϕ1, ϕ2 : X → R are u.s.c. and bounded, then ϕ1,req − sup

X

|ϕ1 − ϕ2| ≤ ϕ2,req ≤ ϕ1,req + sup

X

|ϕ1 − ϕ2| holds on X.

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Regularity properties of the equilibrium envelopes Definition 9 φ : X → [−∞, ∞) is H¨

  • lder with singularities along a proper analytic

subset A ⊂ X if there exist constants c, ̺ > 0 and 0 < ν ≤ 1 such that |φ(z) − φ(w)| ≤ c dist(z, w)ν min{dist(z, A), dist(w, A)}̺ , ∀ z, w ∈ X \ A . Recall that if the class {θ}∂∂ is big then there exists a K¨ ahler current T0 = θ + ddcψ0, where ψ0 is a θ-psh function with analytic singularities such that NAmp

  • {θ}∂∂
  • = {ψ0 = −∞}.

Using the methods developed by Berman-Demailly, Dinh-Ma-Nguyˆ en, we have the following regularity result for ϕreq and ϕeq:

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Theorem 10 Let (X, ω) be a compact Hermitian manifold of dimension n, Σj ⊂ X be irreducible complex hypersurfaces, and let τj > 0, where 1 ≤ j ≤ ℓ. Let α be a smooth closed real (1, 1)-form on X and θ = α −

  • j=1

τjβj , where βj = c1(OX(Σj), gj) . Assume that the class {θ}∂∂ is big and let Z0 := NAmp

  • {θ}∂∂
  • .

Then the following hold: (i) If ϕ : X → R is H¨

  • lder continuous then ϕreq is H¨
  • lder with singularities

along Z0, and ϕeq is H¨

  • lder with singularities along Σ1 ∪ . . . ∪ Σℓ ∪ Z0.

(ii) If ϕ : X → R is continuous then ϕreq is continuous on X \ Z0, and ϕeq is continuous on X \ (Σ1 ∪ . . . ∪ Σℓ ∪ Z0).

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  • 4. Convergence of Fubini-Study currents

Assume: X, L, Σ, τ verify (A)-(D), ∃ ω K¨ ahler form on X, h0 is a fixed smooth Hermitian metric on L, h is a singular metric on L. Write α := c1(L, h0) , h = h0e−2ϕ , so c1(L, h) = α + ddcϕ. ϕ ∈ L1(X, ωn) is called the (global) weight of h relative to h0. h is called continuous, resp. H¨

  • lder continuous, if ϕ is as such on X.

H0

(2)(X, Lp) = Bergman space of L2-holomorphic sections of Lp relative to

the metric hp := h⊗p on Lp and volume ωn on X (S, S′)p :=

  • X

S, S′hp ωn n! , S2

p := (S, S)p

We assume in the sequel that the metric h is continuous and consider H0

0(X, Lp) ⊂ H0(X, Lp) = H0 (2)(X, Lp) .

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dim H0

0(X, Lp) = dp + 1,

Sp

0 , . . . , Sp dp orthonormal basis of H0 0(X, Lp)

Pp(x) =

dp

  • j=0

|Sp

j (x)|2 hp, x ∈ X

(partial) Bergman kernel of H0

0(X, Lp)

Let U ⊂ X open, such that L has a local holomorphic frame eU on U: |eU|h = e−ϕU, Sp

j = sp j e⊗p U , where ϕU ∈ L1 loc(U, ωn), sj ∈ OX(U).

γp |U= 1 2 ddc log dp

  • j=0

|sp

j |2

Fubini-Study current of H0

0(X, Lp)

Have: log Pp |U= log dp

  • j=0

|sp

j |2

− 2pϕU, so log Pp ∈ L1(X, ωn)

1 p γp = c1(L, h) + 1 2p ddc log Pp = α + ddcϕp,

ϕp = ϕ + 1

2p log Pp = global Fubini-Study potential of γp.

Note that ϕp is an α-psh function on X.

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Theorem 11 Let X, L, Σ, τ verify assumptions (A)-(D), assume that (L, Σ, τ) is big and there exists a K¨ ahler form ω on X. Let h be a continuous Hermitian metric

  • n L. Then there exists an α-psh function ϕeq on X such that, as p → ∞,
  • X

|ϕp − ϕeq| ωn → 0, 1 p γp = α + ddcϕp → Teq := α + ddcϕeq, weakly on X. If h is H¨

  • lder continuous then ∃ C > 0, p0 > 1, such that
  • X

|ϕp − ϕeq| ωn ≤ C log p p , for all p ≥ p0. Definition 12 The current Teq from Theorem 11 is called the equilibrium current associated to (L, h, Σ, τ).

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Construction of ϕeq: Let ( X, π, Σ) be a divisorization of (X, Σ) and set

  • L := π⋆L ,
  • h0 := π⋆h0 ,
  • α := π⋆α = c1(

L, h0),

  • ϕ := ϕ ◦ π ,
  • h := π⋆h =

h0e−2

ϕ .

Recall that H0

0(X, Lp) = H0 0(X, Lp, Σ, τ, hp, ωn).

The map S ∈ H0

0(X, Lp) → π⋆S ∈ H0 0(

X, Lp) = H0

0(

X, Lp, Σ, τ, hp, π⋆ωn) is an isometry, so

  • Pp = Pp ◦ π ,
  • γp = π⋆γp ,

are the Bergman kernel function, resp. Fubini-Study current, of H0

0(

X, Lp). Have: 1 p γp = α + ddc ϕp, where ϕp = ϕ + 1

2p log

Pp = ϕp ◦ π.

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Recall: L( X, α, Σ, τ) =

  • ψ ∈ PSH(

X, α) : ν(ψ, x) ≥ τj, ∀ x ∈ Σj, 1 ≤ j ≤ ℓ

  • ϕeq =

ϕeq,

Σ,τ = sup

  • ψ : ψ ∈ L(

X, α, Σ, τ), ψ ≤ ϕ on X

  • Have:
  • ϕeq ∈ L(

X, α, Σ, τ),

  • ϕeq ≤

ϕ on X. Fix a K¨ ahler form ω on X such that ω ≥ π⋆ω. Theorem 13 In the setting of Theorem 11, we have ϕp → ϕeq in L1( X, ωn) as p → ∞. If ϕ is H¨

  • lder continuous on X then there exist C > 0, p0 > 1, such that
  • X

| ϕp − ϕeq| ωn ≤ C log p p , for all p ≥ p0.

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( X, π, Σ) divisorization of (X, Σ): ∃ Y ⊃ Xsing an analytic subset of X, dim Y ≤ n − 2, E = π−1(Y ), π : X \ E → X \ Y is a biholomorphism. Define ϕeq := ϕeq ◦ π−1 on X \ Y ⊂ Xreg. Then, as p → ∞,

  • X\Y

|ϕp − ϕeq| ωn =

  • X\E

| ϕp − ϕeq| π⋆ωn ≤

  • X

| ϕp − ϕeq| ωn → 0. Have π⋆(α + ddcϕeq) = α + ddc ϕeq ≥ 0, so ϕeq is α-psh on X \ Y . ϕeq extends to an α-psh function on X: Let x0 ∈ Y , Ux0 ⊂ X neighborhood on which L has holomorphic frame ex0, |ex0|h0 = e−ρ, ρ smooth function on Ux0, ddcρ = α. ρ ◦ π + ϕeq is psh on π−1(Ux0) \ E, so v := ρ + ϕeq is psh on Ux0 \ Y . v extends to a psh function on Ux0 since X is normal and dim Y ≤ n − 2.

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  • 5. Zeros of random sequences of holomorphic sections

Projectivization of spaces of holomorphic sections Xp := PH0

0(X, Lp) , dp := dim Xp = dim H0 0(X, Lp) − 1 , σp := ωdp FS .

Product probability space (X∞, σ∞) :=

  • p=1

(Xp, σp) Using the Dinh-Sibony equidistribution theorem for meromorphic transforms we obtain: Theorem 14 Let X, L, Σ, τ verify (A)-(D) and h be a continuous Hermitian metric on L. Assume that (L, Σ, τ) is big and there exists a K¨ ahler form ω on X. Then 1 p [sp = 0] → Teq, as p → ∞ weakly on X, for σ∞-a.e. {sp}p≥1 ∈ X∞ .

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Theorem 15 Let X, L, Σ, τ verify (A)-(D), h be a H¨

  • lder continuous Hermitian metric
  • n L. Assume that (L, Σ, τ) is big and there exists a K¨

ahler form ω on X. Then there exists a constant c > 0 with the following property: For any sequence λp > 0, p ≥ 1 such that lim inf

p→∞

λp log p > (1 + n)c, there exist subsets Ep ⊂ Xp such that, for all p sufficiently large, (a) σp(Ep) ≤ cpn exp(−λp/c) , (b) if sp ∈ Xp \ Ep we have

  • 1

p [sp = 0] − Teq, φ

  • ≤ cλp

p φC 2 , ∀ φ ∈ C 2

n−1,n−1(X).

The last estimate holds for σ∞-a.e. {sp}p≥1 ∈ X∞ if p is large enough.

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